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The legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) is a pantropical insect pest of legumes. In West Africa M. vitrata is the most devastating insect pest of cowpea, a food crop providing much-needed, inexpensive protein to farmers and consumers. Various approaches to controlling this pest have been tried, including cultural management, host plant resistance and use of synthetic and botanical pesticides, all with limited success. In this review we present information on the distribution, morphology, molecular characteristics, behavior and host plants of M. vitrata. We give especial attention to innovative management tactics being developed for West Africa, including genetically engineered Bt cowpea, new biopesticides and use of exotic parasitoids. We discuss research needs for enhancing integrated pest management (IPM) for M. vitrata in Africa.

Cowpea stored on smallholders&rsquo, farms suffers serious losses to insect pests. A study conducted in Niger compared five postharvest technologies marketed in sub-Saharan Africa to protect stored grain. Naturally-infested cowpea stored for eight months showed adult Callosobruchus maculatus (F.) mortality of 97% to 100% in the hermetic bags (PICSTM, SuperGrainbagTM, AgroZ&reg, EVAL&trade, and ZeroFly&reg, bags). There was no change in grain damage and weight loss of cowpea stored in hermetic bags. There was, however, a loss of up to 10 to 16% in germination when the grain was stored in hermetic bags. Results observed for grain stored in ZeroFly&reg, bags impregnated with deltamethrin were substantial and similar to those in control woven bags. In both ZeroFly&reg, and woven bags, (1) adult C. maculatus population augmented by 35.7% and 78.6%, (2) increased weight losses of 27.3% and 25.2%, and (3) reduced germination of 37.0% and 28.8%, respectively. After opening the bags, abrasions were noted on the liners of hermetic bags, potential damage that could limit their reuse if they only have a single liner. Smallholder farmers in the Sahel can safely store their cowpea in all the hermetic bags tested. However, further research is needed to mitigate insect damage on liners of hermetic bags to improve their performance and reusability.

Cowpea (Vigna unguiculata Walp.) is the most economically important legume crop in arid regions of sub-Saharan Africa. Cowpea is grown primarily by subsistence farmers who consume the leaves, pods and grain on farm or sell grain in local markets. Processed cowpea foods such as akara (a deep-fat fried fritter) are popular in the rapidly expanding urban areas. Demand far exceeds production due, in part, to a variety of insect pests including, in particular, the lepidopteran legume pod borer (LPB) Maruca vitrata. Genetically engineered Bt-cowpea, based on cry1Ab (Event 709) and cry2Ab transgenes, is being developed for use in sub-Saharan Africa to address losses from the LBP. Before environmental release of transgenic cowpeas, the Bt Cry proteins they express need to be assessed for potential effects on non-target organisms, particularly arthropods. Presented here is an assessment of the potential effects of those Cry proteins expressed in cowpea for control of LPB. Based on the history of safe use of Bt proteins, as well as the fauna associated with cultivated and wild cowpea in sub-Saharan Africa results indicate negligible effects on non-target organisms.

Seed storage is a major challenge for smallholder farmers in developing nations. Purdue Improved Crop Storage (PICS) bags effectively control the postharvest insect pests of cowpea and other crops. Farmers, encouraged by this success, have begun to expand the use of PICS bags for storing other crops. Little is known about how sorghum seed, one of these important crops, fares when stored under hermetic conditions. Accordingly, we stored sorghum seed for six months in either airtight containers (PICS bags or sealed plastic bottles) or open ones (woven polypropylene bags and open plastic bottles). Overall, sorghum seed stored in PICS bags and in sealed plastic bottles maintained its initial moisture level, germination rate and seed weight. Porous polypropylene bags and open plastic bottles lost moisture over six months. We conclude that sorghum seed can be safely stored in hermetic containers without any loss of quality for extended periods of time.

Purdue Improved Crop Storage (PICS) bags have been developed and extended as a way to address grain storage issues faced by smallholder farmers in developing nations. A hermetic technology, PICS bags reduce insect damage to grain significantly while maintaining its quality for many months or longer. Farmers with varying and often small volumes of grain at harvest, may still benefit from alternatives to PICS bags for storing their grain. We evaluated plastic bottles, which may be hermetically sealed, for storing maize grain. Clean maize grain was stored for eight months in sealed and unsealed plastic bottles with half of these bottles being infested by maize weevil (Sitophilus zemais, Motschulsky). Oxygen levels in the bottles were monitored throughout the trial and grain was assessed for moisture content, insect damage, germination rate and insect population size when the study was terminated. Sealed bottles preserved grain quality significantly better than unsealed, infested bottles and as well as non-infested unsealed containers. Plastic soda bottles can be used as hermetic containers for safely storing grain.

The PICS bags, originally developed for cowpea storage, were evaluated for sorghum (Sorghum bicolor) preservation. Batches of 25 kg of sorghum grain were stored in 50 kg PICS or polypropylene (PP) bags under ambient conditions for 12 months and assessed for the presence of insect pests and their damage, seed viability and, oxygen and carbon dioxide variations. The grain was incubated for 35 days to assess whether any insects would emerge. After six months of storage, oxygen levels decreased in the PICS bags compared to polypropylene bags. After 12 months of storage, only two pests, Rhyzopertha dominica and Sitophilus zeamais were found in the PICS bags. However, in PP bags there were additional pests including Tribolium castaneum and Oryzeaphilus mercator and Xylocoris flavipes. Grain weight loss and damage caused by these insects in the PP bags were significantly higher compared to those stored in PICS bags. Germination rates of sorghum grains stored in PP bags decreased significantly while no changes were observed in grains stored in PICS bags when compared to the initial germination. After the incubation post storage period, there was a resurgence of R. dominica in sorghum grains from PICS bags but the population levels were significantly lower compared to polypropylene bags. PICS bags preserved the quality and viability of stored sorghum grains and protected it from key insect pests. The PICS technology is effective for long-term sorghum storage but the potential resurgence of insects in low-oxygen environment calls for further research., Highlights • PICS bags can use for the storage of sorghum grains over a 12-months period. • After 12 months of storage, R. dominica is the only species that emerged from sorghum grains stored in the PICS bags. • R. dominica would be less sensitive to lower O2 concentrations in the storage environment.

Cowpea production in Niger is constrained by biotic and abiotic factors that lead to lower yields and incomes for smallholder farmers. For decades now, efforts have been made to improve cowpea production, including the development and release of improved varieties that are high yielding and resistant or tolerant to pests and diseases. The present study assessed cowpea production constraints on 584 smallholders’ farms in Maradi and Zinder regions of Niger. Estimated parameters consisted of farm size, varieties used and pests and disease prevalence. We found that the average farm size for both regions was 2.10 ha. Local varieties (63%) and IT90K 372-1-2 (30.5%), an improved variety released 25 years ago, were the most-cultivated cowpea varieties. Two recently introduced varieties were planted on less than 4% of fields. Cowpea was grown in association with millet and sorghum on 96.6% of fields. Average cowpea yield for both regions was 253.4 kg ha−1. Five major insect pests and the plant parasite Striga, identified as major production constraints, were negatively correlated with cowpea yields. Diseases were significantly and negatively associated with cowpea yields. To increase cowpea productivity, there is a need to develop and/or promote adapted high-yielding varieties, and to disseminate good agricultural practices to minimize the incidence of pests and diseases.

The quality of maize offered for sale in West African public markets was evaluated by analysing 281 samples collected in 24 markets in Benin, Togo, Ghana and Burkina Faso from February to March 2014. Grain moisture content ranged from 8.5 to 14.4 percent (wt/wt), while extraneous matter content ranged between 0.0 and 2.0% and the proportion of mouldy grains between 0.0 and 0.6%. Insect pest infestations were noted in about one-fourth of the samples with Sitophilus sp., Cryptolestes ferrugineus Stephens, Tribolium sp. and Prostephanus truncatus Horn found at densities varying between 0 and 2.4 individuals per 500 g of grain. Aflatoxin levels exceeding the accepted USA standard of 20 ppb were recorded in only 4.6% of the samples across the four countries. In most locations, grain moisture was within the acceptable range for aflatoxin- and insect-safe storage of maize using hermetic technology such as PICS bags.

Plants produce proteins such as protease inhibitors and lectins as defenses against herbivorous insects and pathogens. However, no systematic studies have explored the structural responses in the midguts of insects when challenged with plant defensive proteins and lectins across different species. In this study, we fed two kinds of protease inhibitors and lectins to the fruit fly Drosophila melanogaster and alpha-amylase inhibitors and lectins to the cowpea bruchid Callosobruchus maculatus. We assessed the changes in midgut cell structures by comparing them with such structures in insects receiving normal diets or subjected to food deprivation. Using light and transmission electron microscopy in both species, we observed structural changes in the midgut peritrophic matrix as well as shortened microvilli on the surfaces of midgut epithelial cells in D. melanogaster. Dietary inhibitors and lectins caused similar lesions in the epithelial cells but not much change in the peritrophic matrix in both species. We also noted structural damages in the Drosophila midgut after six hours of starvation and changes were still present after 12 hours. Our study provided the first evidence of key structural changes of midguts using a comparative approach between a dipteran and a coleopteran. Our particular observation and discussion on plant–insect interaction and dietary stress are relevant for future mode of action studies of plant defensive protein in insect physiology.

Trials of the Purdue Improved Crop Storage (PICS) bag technology for the storage of paddy rice, Oryza sativa L., were conducted in Burkina Faso, Ghana and Niger. Paddy rice naturally infested with insects, the most abundant species being Tribolium spp. and Rhizopertha dominica, was sealed in triple layer PICS bags, or in conventional woven polypropylene sacks. At the end of 7–18 months of storage in PICS bags the number of insects did not increase, the weight of 100 seeds did not change, and the proportion of damaged seeds was not different from that present when the paddy was first put into the bags. By contrast, paddy stored in the conventional way in woven polypropylene bags exhibited weight losses ranging from 3 to 8.7%. In Bolgatanga, Ghana, where paddy was stored for 18 months, germination of paddy kept in the PICS bags was comparable to that present at the beginning of the experiment. PICS bags can be used for the safe, low-cost, insecticide free storage of paddy rice.

Groundnut Arachis hypogaea (L.), is an important legume crop after cowpea Vigna unguiculata (L. Walp) in Niger. However, there has been a decline in its economic importance due to several challenges. A survey of 800 farmers was conducted in 40 villages in the Maradi and Zinder regions to assess constraints and opportunities to improve groundnut production and marketing. Average land size and yield varied by region: 1.3 ha per farmer and 461.3 kg ha-1 in Maradi, and 1.7 ha per farmer and 417.2 kg ha-1 in Zinder. Insect pests (aphids) were the most important production constraint. Groundnut is typically stored for six to eight months after harvest but 91% of farmers do not take any precautions to protect the grain. Storage enables farmers to earn high profit margins of up to 33 and 113% for unshelled and shelled groundnuts, respectively. Most farmers (71.5%) sell their groundnut in unshelled form in local and urban markets. Traders are the main buyers according to 61.7% of farmers while processors were mentioned as purchasers by less than 20%. Sales are mostly done by individual farmers while very little is sold through cooperatives. Given that groundnut is a profitable crop adapted to the Sahelian zone, there is need to improve its production, storage, and value addition through processing.

Groundnut seeds are prone to quality deterioration and damage due to improper storage. Hermetic storage of pods offers a novel, sustainable and ecologically safe alternative over traditional methods. In this paper, we demonstrate the efficacy of triple-layer “Purdue Improved Crop Storage (PICS)” bags, (that comprises of two inner high density polyethylene bags and one outer woven polypropylene bag), for protecting pods from quality deterioration, damage by bruchids (Caryedon serratus) and aflatoxin contamination (Aspergillus flavus). Custom made triple-layer bags were used and pods (of cv ICGV 91114) were placed @ 2 kg/bag. Over four months of storage under ambient conditions, triple-layer bags supported retention of seed weight, germinability and oil content significantly better than cloth bags. Further, under both natural and artificial infestations with A. flavus, seed aflatoxins levels were lower in PICS bags compared to cloth bags. Toxin accumulation in PICS bags deliberately infested with bruchids and A. flavus was less compared to cloth bags under similar conditions. Bruchid damage to pods was less in PICS bags versus cloth bags in all cases. Our results suggest the superiority of triple-layer PICS bags over cloth bags in protecting seed viability, seed weight and oil content while safeguarding the groundnuts from bruchids and retarding toxin accumulation.

We surveyed 1293 farmers and traders in southern Niger to learn about their grain storage practices and their views on the storage pest problem. We identified the insect species found in samples obtained from 40 localities in three regions of the country. We stored 371 grain samples collected from respondents in the laboratory for seven months to allow populations of the insects present to develop and emerge and the resultant grain weight loss to be determined. The commodities most commonly stored in Niger were millet and sorghum, kept in storage on average for about 6 months by 53% and 80% of respondents respectively. When millet samples from respondents were kept in the laboratory for seven months, two pests were found, the rice moth Corcyra cephalonica Stainton, and Tribolium spp. This millet experienced a weight loss of 17.1% during seven months storage. Tribolium castaneum Herbst, Sitophilus granarius L., Cryptolestes spp, Sitotroga cerealella Oliver, Trogoderma granarium Everts, Rhyzopertha dominica F. and C. cephalonica were found in stored sorghum, which lost 10.1% weight after seven months. Eleven other grains or foods were stored by 2.9–24.4% of respondents. Recorded weight losses were 15.9% for groundnuts, 12.6% for paddy rice, 7.6% for sesame and 7.4% for maize. Seeds of Hibiscus sabdariffa L. and Bambara groundnut were essentially destroyed by bruchids during storage, mean weight losses being 83.9% and of 61.8% respectively. Most respondents took no measures to control insect pests in their stored grains. Food security and quality in Niger would be greatly improved if Africa-manufactured technology that is safe, low-cost, insecticide free, and widely available could be implemented for postharvest storage of food grains.

Purdue Improved Crop Storage Bags (PICS) bags are hermetic containers consisting of two inner layers of high-density polyethylene (HDPE) surrounded by an outer woven polypropylene bag. They have proven effective in preventing losses of stored cowpea grain to the cowpea bruchid, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae) and perform well with other dry grains attacked by several species of postharvest pests. We tested PICS bags against the rice weevil, Sitophilus oryzae L. (Coleoptera: Curculionidae), a common stored grain pest. Storing rice weevil infested wheat in PICS bags arrested weevil population growth and preserved the grain well. The air surrounding infested wheat held in PICS bags had lower oxygen and higher carbon dioxide levels compared to the ambient atmosphere. Seed germination declined over time in infested PICS bags, but less so than did grain held in infested woven bags. Low-cost, durable, pesticide-free PICS technology offers an inexpensive, practical and useful way to protect wheat against rice weevil.

Hermetic storage containers are often used by farmers to protect their harvested grain from insect damage and ultimately stop insect population development. Sometimes holes in a storage container are created by insects or by accident; such holes may reduce the effectiveness of the hermetic storage unit. Using cowpea grain and the cowpea bruchid, Callosobruchus maculatus (F), we investigated the degree to which holes in a hermetic storage container wall affect the level of grain damage. When there were low numbers of holes, seed damage increased markedly with each additional hole. The grain itself contributed a barrier to oxygen diffusion through the grain mass. If holes in the container wall were patched with a single layer of HDPE film, grain damage was indistinguishable from that seen under full hermetic conditions. We provide evidence that a single layer of woven polypropylene contributes a small but measurable barrier to oxygen penetration into the container.

Dry mung bean and pigeonpea grains that had sustained some insect damage but fumigated before the start of the experiment were stored in triple-layer hermetic bags (Purdue Improved Crop Storage (PICS™ bags) or woven polypropylene (PP) bags for 6 months. Some of the bags were artificially infested with cowpea bruchid Callosobruchus maculatus (F.) (PICS1, PP1) while others were not (PICS0, PP0). In an additional trial, PP bags containing the grains were treated with Actellic Super ® dust before being artificially infested (PP1Ac). Moisture content, live adult C. maculatus count, grain damage, weight loss, and seed germination were determined on a monthly basis. At six months, moisture contents of grain stored in PICS and PP bags remained below 12%. Storage in PICS bags halted multiplication of C. maculatus , and the initial damage level and weight of grains did not change. Conversely, in the PP bags, C. maculatus populations increased massively and seed damage reached 71.8 ± 1.9%, 76.9 ± 0.4%, and 60.3 ± 0.6% corresponding to weight losses of 14.5 ± 0.1%, 16.5 ± 0.2% and 12.5 ± 0.1% in PP0, PP1 and PP1Ac, respectively, in mung beans. With the pigeonpeas, seed damage reached 55.1 ± 0.6%, 95.7 ± 0.4% and 75.8 ± 0.9%, corresponding to weight losses of 13.0% ± 0.3%, 26.2 ± 0.2% and 13.5 ± 0.1%, in PP0, PP1 and PP1Ac, respectively. PICS bags are an effective tool for preserving mung beans and pigeonpeas against C. maculatus attack, and their performance is superior to that of Actellic Super ® dust.

Pigeonpea [Cajanus cajan (L.) Millsp.] seed stored in triple layer Purdue Improved Cowpea Storage (PICS) bags for eight months retained germination and seed integrity significantly better than seed stored in traditional gunny bags. PICS bags prevented major damage caused by bruchids (Callosobruchus maculatus F.), while grain stored in gunny bags suffered severe losses. The aflatoxin levels in stored seed were low and not significantly different between the two storage systems. The levels of O2 in PICS bags artificially infested with C. maculatus dropped rapidly during the first month of storage while the levels of CO2 increased. Even in absence of bruchids (noninfested seed) PICS bags preserved seed germination for extended periods of time better than gunny bags; possibly due to the higher and more stable relative humidity inside the PICS bags. Higher seed germination would result in improved plant stands in the field and subsequent higher yields and increased productivity. Thus, PICS bags have shown potential to positively impact the economy of pigeonpea farmers in the semi-arid tropics.

Maize is a key food crop in West Africa, where Benin, Ghana, Burkina Faso and Nigeria account for most of the regional production. Storage pests are major constraints in the maize value chain, with losses reaching 30%. Simple, low-cost triple bagging technology (now known as PICS – Purdue Improved Crop Storage) originally developed for postharvest storage of cowpea was evaluated for applicability to maize storage. Thirteen test units employing PICS bag were set up in July and August 2012 at eleven localities in Benin, Burkina Faso and Ghana. Each trial unit consisted of 3 or 4 PICS bags of 50 kg capacity and 2 woven control bags. We used locally purchased naturally infested maize that had relatively high levels of infestation with Prostephanus truncatus Horn, Sitophilus zeamais Motschulsky, 1855 and/or Rhyzopertha dominica (F.) (seven localities) or lightly infested maize showing little or no evidence of damage (four localities). After 6.5 months of storage in PICS bags, there was 95–100% insect mortality at all sites. The percentage of damaged seeds and the 100 seeds weights in PICS bags were unchanged from what was recorded at the time the experiment was set up. Seed viability was well maintained; germination rates of seeds from the PICS bags did not differ from that observed at the beginning of the experiment. Aflatoxin tests were carried out on 245 samples, with 53% having levels above 20 ppm in both PICS and woven bags. Samples from PICS bags tended to be less contaminated than those from woven bags. PICS bags can be used for maize storage even in areas with high prevalence of P. truncatus, but storage of maize should begin soon after harvest and drying to minimize bag damage that can occur when very high numbers of P. truncatus are present.

Clean shelled maize was stored in woven polypropylene (PP) or triple layer polyethylene (PICS™) bags in the presence of Prostephanus truncatus Horn (PP1; PICS1) or absence of it (PP0; PICS0) at ambient conditions for six months. Moisture content, live insect population, grain damage, weight loss, and germination were analyzed on a monthly basis. Temperature and relative humidity in both PICS- and PP-bag setups were monitored, as well as the oxygen and carbon dioxide levels in the PICS bags. Overall, maize stored in PICS bags had significantly lower (P

Hermetic or airtight storage of grain to suppress development of destructive populations of storage insect pests is an ancient technology that is finding modern applications in developing nations. Unprotected cowpea grain can be destroyed by unchecked growth of the bruchid, Callosobruchus maculatus (Walp). If the grain is kept in triple-layer hermetic plastic bags, losses are averted. The history, development and mode of action of triple-layer bagging for cowpea storage is reviewed here, as are lessons learned while bringing the technology to low-resource farmers in the developing nations of West and Central Africa. The success of the technology owes in part to the engagement of low resource farmers at virtually all stages of development, testing and extension of the technology.

Experiments were conducted to evaluate the performance of hermetic triple bagging using Purdue Improved Crop Storage (PICS) bags for storage of Bambara groundnut ( Vigna subterranea (L.) Verdc.). One set of experiments used grain heavily infested by Callosobruchus maculatus (F.) while a second set began with a low level infestation. Each experiment consisted of V. subterranea grain kept in four replicate 50 kg PICS bags or two replicate woven bags as controls. Two to five days after the beginning of the experiments, oxygen level inside the bags averaged about 21% (v/v) in the controls but decreased significantly in PICS bags, reaching 10% (v/v) with the heavily infested grain but falling only slightly in the lightly infested grain. After 7 months of storage, (i) the number of C. maculatus adults found between and within the grains, (ii) the 100 seed weight, (iii) the number of seed with holes, and (iv) the percentage germination of grain stored in PICS bags did not differ from what had been measured on the day that the experiment was set up. In woven bags, by contrast, there was a massive increase in C. maculatus numbers with means of 309 and 251 adults per 500 g in heavily and lightly infested grain, respectively. Grain weight losses in the woven bag controls ranged from 8 to 19% and the percentage of C. maculatus emergence holes per 100 seed increased from 51 to 135%.

When cowpea bruchid-infested cowpea grain was stored for four-plus months in Purdue Improved Cowpea Storage (PICS™) bags or in commercially-available GrainPro SuperGrain™ bags, preservation of the grain was equally good in both types of bags. In both bag types oxygen (O2) levels dropped rapidly during the first 24 h after closure, eventually reaching levels of 1–3 percent by volume (v/v). With both types of bag there was an initial rise in temperature during the first 24 h, followed by a decline, in time reaching ambient. Over the four-plus months of the experiment damage levels did not significantly increase in either type of bag while control grain kept in a conventional woven plastic bag suffered severe damage. Most of the insects found in both GrainPro and PICS bags at the end of the experiment were dead. The single layer SuperGrain™ bags showed more bruchid holes than did triple-layer PICS bags, which had no holes penetrating through both of the inner high density polyethylene (HDPE) layers, meaning that an intact O2 barrier remained in place even after the inner HDPE layer was holed. Farmers who wish to store their cowpea grain with either technology can choose between the two types of bags, taking into account price, availability and durability.

From 2007 through 2011 experiments were conducted and observations made in the West African country of Niger to address questions or concerns raised by farmers and extension workers about the Purdue Improved Cowpea Storage (PICS) triple bagging technology being widely disseminated in the country. When 518 triple bags stored by farmers in different villages across southern Niger were studied, the airspaces within the bags typically contained reduced levels of O 2 while CO 2 was increased. Bagged stored cowpea grain was much less damaged and had higher market value compared to grain for sale in the local markets. Two HDPE plastic liners rendered the system substantially airtight and improved preservation of the grain compared to a single HDPE liner. The concentrations of O 2 and CO 2 were similar along the length of the triple bag, in top, bottom and middle sections. Cowpea grain stored for 18 months in PICS bags retained high rates of germination. Briefly opening bags that had been closed for long periods did not affect the preservation of the grain. Treating the contents of the triple bag with phostoxin did not enhance preservation. Leaving the triple bag containing infested cowpea open for several days prior to closure increased the risk of blemishes or holes in the HDPE liners caused by cowpea bruchid, Callosobruchus maculatus (F.) adults.

Postharvest insect pests threaten the nutritional and financial security of smallholder farmers in the developing world. Hermetic storage, a technology that protects grain against insects by blocking their supply of oxygen, alleviates the problem of insect-caused losses. PICS (Purdue Improved Crop Storage) bags represent one hermetic technology that improves food availability and incomes of farmers. The polyethylene liners of PICS bags are sometime damaged during use, acquiring small holes or tears. Observations in the laboratory and field suggest that insect development remains localized around the point where the bag is damaged. We hypothesized that the grain within a hermetic container that has minimal localized damage (such as an insect hole), helps retard leakage of oxygen into the bag and contributes to limiting insect damage and to the overall protective effect. To test this hypothesis, we filled 4 cm dia. by 10 cm long PVC pipes with Callosobruchus maculatus (F.) infested cowpeas and sealed them with caps having a single, insect-sized hole in its center. A vertical tube positioned above the cowpea-filled PVC pipe was filled with one of three different grains (sesame, sorghum, and maize) to different depths (0, 5, 15, 30, 50 cm). Seed size and grain barrier depth significantly reduced the level of bruchid damage to the stored cowpea in the PVC container. Smaller sized grains used for the barriers retarded insect development more effectively than larger sized grains, while deeper grain depth was more effective than shallower barriers. The grain held in a hermetic container contributes in a small, but significant, way to the effectiveness of the containers., Highlights • Grain may reduce airflow into damaged hermetic container and reduce insect damage to seed. • Infested cowpea was buried to different grain depths to determine its effects on damage severity. • Greater depth resulted in slower population growth and less seed damage. • Smaller seed size reduced adult development and larval activity.

Interest in using hermetic technologies as a pest management solution for stored grain has risen in recent years. One hermetic approach, Purdue Improved Crop Storage (PICS) bags, has proven successful in controlling the postharvest pests of cowpea. This success encouraged farmers to use of PICS bags for storing other crops including maize. To assess whether maize can be safely stored in PICS bags without loss of quality, we carried out laboratory studies of maize grain infested with Sitophilus zeamais (Motshulsky) and stored in PICS triple bags or in woven polypropylene bags. Over an eight month observation period, temperatures in the bags correlated with ambient temperature for all treatments. Relative humidity inside PICS bags remained constant over this period despite the large changes that occurred in the surrounding environment. Relative humidity in the woven bags followed ambient humidity closely. PICS bags containing S. zeamais-infested grain saw a significant decline in oxygen compared to the other treatments. Grain moisture content declined in woven bags, but remained high in PICS bags. Seed germination was not significantly affected over the first six months in all treatments, but declined after eight months of storage when infested grain was held in woven bags. Relative damage was low across treatments and not significantly different between treatments. Overall, maize showed no signs of deterioration in PICS bags versus the woven bags and PICS bags were superior to woven bags in terms of specific metrics of grain quality.

Modified atmospheres present a residue-free alternative to fumigants for controlling postharvest pests of grain during storage. How sub-lethal applications of this method affects the reproductive fitness of target pests, however, is still not fully understood. We examined how low levels of ambient oxygen influence the reproduction of the female cowpea bruchid (Callosobruchus maculatus), a pest of cowpea. We used three low-oxygen atmospheres-2%, 5% and 10% (v/v) oxygen-and observed their effects on: (1) the number of eggs laid by bruchids compared to insects held in normoxic (~20% oxygen) conditions; (2) the total number of eggs laid; and (3) the number of progeny that reached maturity. Low oxygen did not significantly affect the number of eggs laid during 48 or 72 h of exposure, but 2% and 5% oxygen did negatively affected total egg production. Increasing the exposure time from 48 to 72 h further depressed lifetime reproductive output. Maternal and egg exposure to hypoxia reduced the number of progeny that reached adulthood. Lower adult emergence was observed from eggs laid under low oxygen and longer exposure times. These data demonstrate that hermetic conditions depress the egg-laying behavior of cowpea bruchids and the successful development of their progeny.

Triple bagging technology for protecting postharvest cowpea grain from losses to the bruchid, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae) is currently being adopted on a fairly large scale in ten West and Central African countries, including Niger. The triple bag consists of two inner high-density polyethylene bags acting as oxygen barriers, which in turn are encased in an outer woven polypropylene bag that serves primarily for mechanical strength. These hermetic bags, available in either 50 or 100 kg capacity, are called Purdue Improved Cowpea Storage (PICS) bags. Adoption of PICS technology in West and Central Africa has been driven by its effectiveness, simplicity, low cost, durability, and manufacture within the region. From surveys on adoption we discovered that farmers have begun to re-use bags they had used the previous year or even the previous two years. In the present study, we compared the performance of three different types of PICS bags: (1) new 50 kg (2) new 100 kg bags and (3) once-used 50 kg bags, all filled with naturally infested untreated cowpeas. In these PICS bags the O 2 levels within the bags initially fell to about 3 percent (v/v) while the CO 2 rose to nearly 5 percent (v/v). After five months of storage, new and used 50 kg bags and new 100 kg bags preserved the grain equally well. There were greatly reduced numbers of adults and larvae in the PICS bags versus the controls, which consisted of grain stored in single layer woven bags. The proportion of grain having C. maculatus emergence holes after five months of storage in PICS bags was little changed from that found when the grain was first put into the bags. The PICS technology is practical and useful in Sahelian conditions and can contribute to improved farmers' incomes as well as increase availability of high quality, insecticide-free cowpea grain as food.

The legume pod borer,Maruca vitrata, is an endemic insect pest that causes significant yield loss to the cowpea crop in West Africa. The application of population genetic tools is important in the management of insect pests but such data onM. vitratais lacking. We applied a set of six microsatellite markers to assess the population structure ofM. vitratacollected at five sites from Burkina Faso, Niger and Nigeria. Observed polymorphisms ranged from one (marker 3393) to eight (marker 32008) alleles per locus. Observed and expected heterozygosities ranged from 0.0 to 0.8 and 0.0 to 0.6, respectively. Three of the loci in samples from Nigeria and Burkina Faso deviated significantly from Hardy-Weinberg Equilibrium (HWE), whereas no loci deviated significantly in samples from Niger. Analysis of molecular variance (AMOVA) indicated that 67.3% level of the genetic variation was within individuals compared to 17.3% among populations. A global estimate ofFST=0.1 (ENA correctedFST=0.1) was significant (P⩽0.05) and corroborated by pairwiseFSTvalues that were significant among all possible comparisons. A significant correlation was predicted between genetic divergence and geographic distance between subpopulations (R2=0.6,P=0.04), and cluster analysis by the program STRUCTURE predicted that co-ancestry of genotypes were indicative of three distinct populations. The spatial genetic variance amongM. vitratain West Africa may be due to limited gene flow, south-north seasonal movement pattern or other reproductive barriers. This information is important for the cultural, chemical and biological control strategies for managingM. vitrata.

Several technologies reputedly minimize losses of stored cowpea grain to bruchid beetles on low resource farms in Africa. Side by side comparison of these different postharvest storage methods can provide the basis for deciding which performs best. We compared six different technologies for cowpea storage: (1) grain mixed with ash; (2) mixed with sand; (3) fumigated with phostoxin; (4) admixed with the stems and leaves of Boscia senegalensis (Pers) Lam ex Poir, a potential botanical insecticide; (5) disinfested using a solar heater, and; (6) hermetically sealed in triple-layer plastic bags. Sampling was done at thirty-day intervals over five months of storage. Counts were made of (i) adult emergence holes, (ii) dead larvae and (iii) surviving bruchid larvae and adults. Controls, which consisted of infested cowpea grain stored in cloth bags, were damaged extensively. Boscia senegalensis -treated grain suffered similar severe damage. All other treatments suppressed bruchid population increases as was evident from the much lower counts of emergence holes and lower numbers of surviving or dead insects.

We surveyed three locations in West Africa, two in northern Nigeria and one in southern Niger, for the presence of wild alternative hosts of the legume pod borer (LPB) Maruca vitrata Fabricius, which could serve as natural unstructured refugia for transgenic Bacillus thuringiensis ( Bt )-cowpea. We surveyed a total of 67 sites in proximity to cowpea fields in the Sudan Savannah (Kano, Nigeria), the Northern Guinea Savannah (Zaria, Nigeria) and the Sahel Savannah (Maradi, Niger) ecological zones. The results indicate that alternative host plants for LPB are scarce or absent during the cowpea-growing season in these areas.

Bowman-Birk inhibitor (BBI) is toxic when fed to certain insects, including the fruit fly, Drosophila melanogaster. Dietary BBI has been demonstrated to slow growth and increase insect mortality by inhibiting the digestive enzymes trypsin and chymotrypsin, resulting in a reduced supply of amino acids. In mammals, BBI influences cellular energy metabolism. Therefore, we tested the hypothesis that dietary BBI affects energy-associated pathways in the D. melanogaster midgut. Through microarray and metabolomic analyses, we show that dietary BBI affects energy utilization pathways in the midgut cells of D. melanogaster. In addition, ultrastructure studies indicate that microvilli are significantly shortened in BBI-fed larvae. These data provide further insights into the complex cellular response of insects to dietary protease inhibitors.

The insect digestive system is the first line of defence protecting cells and tissues of the body from a broad spectrum of toxins and antinutritional factors in its food. To gain insight into the nature and breadth of genes involved in adaptation to dietary challenge, a collection of 20 352 cDNAs was prepared from the midgut tissue of cowpea bruchid larvae (Callosobruchus maculatus) fed on regular diet and diets containing antinutritional compounds. Transcript responses of the larvae to dietary soybean cystatin (scN) were analysed using cDNA microarrays, followed by quantitative real-time PCR (RT-PCR) confirmation with selected genes. The midgut transcript profile of insects fed a sustained sublethal scN dose over the larval life was compared with that of insects treated with an acute high dose of scN for 24 h. A total of 1756 scN-responsive cDNAs was sequenced; these clustered into 967 contigs, of which 653 were singletons. Many contigs (451) did not show homology with known genes, or had homology only with genes of unknown function in a Blast search. The identified differentially regulated sequences encoded proteins presumptively involved in metabolism, structure, development, signalling, defence and stress response. Expression patterns of some scN-responsive genes were consistent in each larval stage, whereas others exhibited developmental stage-specificity. Acute (24 h), high level exposure to dietary scN caused altered expression of a set of genes partially overlapping with the transcript profile seen under chronic lower level exposure. Protein and carbohydrate hydrolases were generally up-regulated by scN whereas structural, defence and stress-related genes were largely down-regulated. These results show that insects actively mobilize genomic resources in the alimentary tract to mitigate the impact of a digestive protease inhibitor. The enhanced or restored digestibility that may result is possibly crucial for insect survival, yet may be bought at the cost of weakened response to other stresses.

One function of plant lectins such as wheat germ agglutinin is to serve as defences against herbivorous insects. The midgut is one critical site affected by dietary lectins. We observed marked cellular, structural and gene expression changes in the midguts of Drosophila melanogaster third instar larvae that were fed wheat germ agglutinin. Some of these changes were similar to those observed in the midguts of starved D. melanogaster. Dietary wheat germ agglutinin caused shortening, branching, swelling, distortion and in some cases disintegration of the midgut microvilli. Starvation was accompanied primarily by shortening of the microvilli. Microarray analyses revealed that dietary wheat germ agglutinin evoked differential expression of 61 transcripts; seven of these were also differentially expressed in starved D. melanogaster. The differentially transcribed gene clusters in wheat germ agglutinin-fed larvae were associated with (1) cytoskeleton organization; (2) digestive enzymes; (3) detoxification reactions; and (4) energy metabolism. Four possible transcription factor binding motifs were associated with the differentially expressed genes. One of these exhibited substantial similarity to MyoD, a transcription factor binding motif associated with cellular structures in mammals. These results are consistent with the hypothesis that wheat germ agglutinin caused a starvation-like effect and structural changes of midgut cells of D. melanogaster third-instar larvae.

Oligoarray analysis was used to determine the number and nature of genes expressed in third instar Drosophila melanogaster larval midguts. The majority of transcripts were associated with protein synthesis and metabolism. Serine proteases were the main proteolytic enzymes detected. Some 40% of the cytochrome P450 genes and 74% of the glutathione S transferases (GSTs) in the genome of D. melanogaster were observed to be expressed in the midgut by oligoarray analysis. We also identified potential transcription factor binding motifs (TFBMs) of P450s, GSTs and carboxylesterases. Many of the midgut-expressed GST genes contained candidate TFBMs homologous to TFBMs in mammals that have been associated with responses to oxidative stress. We also investigated the response of GSTs in the midgut to dietary H 2 O 2 , which showed a dosagebased differential response.

Avidin, a large protein from egg whites, powerfully binds biotin, a vitamin for many insects. When avidin was incorporated into the diets of larval Callosobruchus maculatus (F.), the cowpea bruchid, at relatively low levels (10–30 ppm), there was a marked dose-dependent increase in mortality, as well as a small increase in the developmental time of survivors. Avidin toxicity was prevented when biotin was added to the diet together with avidin. Sub-lethal doses of avidin caused reductions in fecundity. Avidin had no effect on the larval feeding rates during the first three instars, even when the larvae were consuming amounts of the protein that would later cause death. In the fourth instar there was a dose-dependent reduction in the rates of feeding as the avidin level in the food increased. Death of the C. maculatus larvae usually occurred at the pupal/adult stage still within the host seed. Streptavidin, a biotin-binding protein from a bacterial source, had effects similar to chicken egg avidin.

Plants produce proteins such as protease inhibitors and lectins as defenses against herbivorous insects and pathogens. However, no systematic studies have explored the structural responses in the midguts of insects when challenged with plant defensive proteins and lectins across different species. In this study, we fed two kinds of protease inhibitors and lectins to the fruit fly Drosophila melanogaster and alpha-amylase inhibitors and lectins to the cowpea bruchid Callosobruchus maculatus . We assessed the changes in midgut cell structures by comparing them with such structures in insects receiving normal diets or subjected to food deprivation. Using light and transmission electron microscopy in both species, we observed structural changes in the midgut peritrophic matrix as well as shortened microvilli on the surfaces of midgut epithelial cells in D. melanogaster . Dietary inhibitors and lectins caused similar lesions in the epithelial cells but not much change in the peritrophic matrix in both species. We also noted structural damages in the Drosophila midgut after six hours of starvation and changes were still present after 12 hours. Our study provided the first evidence of key structural changes of midguts using a comparative approach between a dipteran and a coleopteran. Our particular observation and discussion on plant–insect interaction and dietary stress are relevant for future mode of action studies of plant defensive protein in insect physiology.

Targeting multiple digestive proteases may be more effective in insect pest control than inhibition of a single enzyme class. We therefore explored possible interactions of three antimetabolic protease inhibitors fed to cowpea bruchids in artificial diets, using a recombinant soybean cysteine protease inhibitor scN, an aspartic protease inhibitor pepstatin A, and soybean Kunitz trypsin inhibitor KI. scN and pepstatin, inhibiting major digestive cysteine and aspartic proteases, respectively, significantly prolonged the developmental time of cowpea bruchids individually. When combined, the anti-insect effect was synergistic, i.e., the toxicity of the mixture was markedly greater than that of scN or pepstatin alone. KI alone did not impact insect development even at relatively high concentrations, but its anti-insect properties became apparent when acting jointly with scN or scN plus pepstatin. Incubating KI with bruchid midgut extract showed that it was partially degraded. This instability may explain its lack of anti-insect activity. However, this proteolytic degradation was inhibited by scN and/or pepstatin. Protection of KI from proteolysis in the insect digestive tract thus could be the basis for the synergistic effect. These observations support the concept that cowpea bruchid gut proteases play a dual role; digesting protein for nutrient needs and protecting insects by inactivating dietary proteins that may otherwise be toxic. Our results also suggest that transgenic resistance strategies that involve multigene products are likely to have enhanced efficacy and durability.

Fumigated dry common beans (Phaseolus vulgaris L.) that were artificially infested with Acanthoscelides obtectus Say, and others that were not artificially infested, were stored in hermetic triple-layer PICS (Lela Agro, Kano, Nigeria) or woven polypropylene (PP) bags for 6 mo at ambient laboratory temperature conditions of 22.6 ± 1.9°C and 60.1 ± 4.3% relative humidity. In an additional trial, beans contained in PP bags were treated with Actellic Super dust before introducing A. obtectus. Moisture content, number of live adult A. obtectus, seed damage, weight loss, and seed germination were determined at monthly intervals. At 6 mo, beans stored in PICS bags retained higher moisture than those stored in PP bags, but in all treatments the moisture level remained below that recommended for safe storage of beans. In the PICS bags, proliferation of A. obtectus did not proceed and at 6 mo, beans stored in these bags did not have insect-inflicted seed damage or weight loss. In contrast, seed damage and weight loss in PP bags exceeded economic threshold after 1 mo in the absence of Actellic Super dust (Syngenta Crop protection AG, Basle, Switzerland), and after 2 mo in the presence of it. Germination of beans stored in PP bags decreased greatly whereas the beans stored in PICS bags did not show reduced germination. Chemical free storage of common beans in PICS bags protects them against damage by A. obtectus.

The cowpea bruchid, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchini), is aworldwide pest of stored cowpea grain [ Vigna unguiculata (L.) Walp. (Leguminosae)], causing tensof millions of dollars’ worth of damage annually. One method of managing this pest involves plantingcultivars whose seeds are resistant to bruchids. Despite extensive research, we still do not know themechanism by which TVu 2027, the original resistant cowpea line, resists C. maculatus . Using micro-CAT (computerized axial tomography) scan imaging, we visualized the feeding patterns of bruchidsliving and growing within cowpea seeds. We present evidence that an interior zone in TVu 2027 seedsis responsible for the high mortality and developmental de lays experienced by avirulent larval bruchids.We observed that both virulent as well as avirulent bruchid strains have different feeding patterns inTVu 2027 seeds compared to susceptible seeds. It appears that the resistance factor is most concen- trated in a zone in each cotyledon adjacent to the air space separating the two seed halves.

Three recombinant soybean cysteine proteinase inhibitors (rSCPIs), L1, R1 and N2, were assessed for their potential to inhibit the growth and development of three major agricultural crop pests known to utilize digestive cysteine proteinases: Western corn rootworm ( Diabrotica virgifera virgifera, WCR), Colorado potato beetle ( Leptinotarsa decemlineata, CPB) and cowpea weevil ( Callosobruchus maculatus, CW). In vitro experiments showed that cysteine proteinase activities in the crude gut extracts of the WCR, CPB, and CW were inhibited to various degrees by the three rSCPIs. Of the three rSCPIs tested, N2 was most effective in inhibiting the crude gut extract of WCR, CPB, and CW (50% inhibition at 5 × 10 −8 , 5 × 10 −8 , and 3 × 10 −7 M, respectively). The L1 was the least potent of the three CPIs tested, with 50% inhibition at 5 × 10 −6 M of the crude gut extracts of WCR. Results of in vivo experiments conducted to assess the effect of the three rSCPIs on the vital growth parameters of WCR, CPB and CW were consistent with results of the in vitro experiments.