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Trap crops are plants grown along with the main crop in order to manipulate insect behavior to manage the insect pests and are used as a cultural management strategy in several crops. Trap crops also provide habitat to natural enemies and can reduce the need for insecticides and hence reduce the development of insecticide resistance. The attractiveness of the trap crop, the timing of planting, and the space it occupies are major factors to consider before selecting and using a trap crop. The addition of semiochemicals and incorporation of ‘stimulo-deterrent diversion’ can increase the efficiency of trap crops. The important insect pests of cereal crops reported to managed by using trap crops include the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), on wheat and the stem borers Chilo partellus (Swinhoe) and Busseola fusca (Fuller) on maize and sorghum. Other insect pests such as soil-dwelling wireworms [Agriotes obscurus L., Limonius californicus (Mannerheim) (Coleoptera: Elateridae)] on potatoes and the aphids Schizaphis graminum (Rondani) (Hemiptera: Aphididae), and Rhopalosiphum padi L. on wheat and the brown planthopper Nilaparvata lugens (Stål) on rice are also possible to manage by using trap crops. Cereal crops such as maize and wheat are sometimes themselves used as trap crops, yet there have been only a handful of attempts made to use trap crops in cereal crops. The major limiting factors in using trap crops in cereal crops are environmental conditions, variation in landscape and cultivation practices. Nonetheless, trap crops remain an important tool of integrated pest management, and future studies should work to improve the efficacy, cost efficiency, and availability of alternative trap crops for use in cereal cultivation.

Transgenic Bt maize expressing Cry insecticidal δ-endotoxins of Bacillus thuringiensis has been cultivated in South Africa for the control of Busseola fusca since 1998. Busseola fusca is resistant to Cry1Ab Bt maize at many localities throughout the maize production region. Pre-release evaluation (1994-1996) of the inherent susceptibility and post-release assessments (1998-2011) of resistance status of B. fusca focused on a limited number of pest populations. This study reports the current levels of susceptibility of 10 B. fusca populations evaluated between 2013 and 2017 and compared this data with previously reported data on the survival of this pest on Bt maize, including data of pre-release evaluations done during 1994 and 1995. Larval feeding bioassays in which plant tissue of maize events expressing either Cry1Ab or Cry1A.105+Cry2Ab2 (stacked event) proteins were conducted and survival and different life history parameters recorded. Results show a shift in levels of susceptibility of B. fusca to Bt maize. Pre-release evaluation of the single-gene event showed very low larval survival on Bt maize leaf tissue while studies 10 yr later and the current study reported survival of up to 40% and 100% on Cry1Ab maize, respectively. While no larvae completed their life cycle on the stacked event, higher LT50 values in this study indicate a shift in susceptibility of B. fusca to the stacked-gene event and highlight the importance of baseline information and monitoring of pest populations for their susceptibility to Bt maize.

Previous studies into third trophic level exposure of Chrysoperla spp. (Neuroptera: Chrysopidae) to Cry1Ab proteins produced by Bt crops yielded contradicting results. These contradictions were largely ascribed to differences in prey quality and exposure methods. In this study, we used healthy prey to expose lacewing larvae to Cry1Ab protein produced by Bt maize, and also determined the concentration of this protein at different trophic levels. Experiments were conducted in which Chrysoperla pudica (Navás) larvae were fed different diets which included aphids and healthy Bt-resistant Busseola fusca (Fuller) (Lepidoptera: Noctuidae) larvae feeding on Bt maize tissue. Lacewing larval and pupal development times as well as overall mortality were determined. The concentration of Cry1Ab protein in B. fusca larvae were fourfold reduced compared with that in leaf tissue and was below detection level in lacewing larvae. Survival to the pupal stage was higher than 96% in all treatments. Larval and pupal development periods did not differ significantly between treatments in which prey fed on Bt or non-Bt maize. This study showed feeding on healthy prey that consumed Cry1Ab protein has no adverse effect on the biology of C. pudica.

The host plant range of pests can have important consequences for its evolution, and plays a critical role in the emergence and spread of a new pest outbreak. This study addresses the ecological genetics of the indigenous African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), in an attempt to investigate the evolutionary forces that may be involved in the recent host range expansion and establishment of this species in Ethiopian and southern African sugarcane. We used populations from Ethiopia, Zimbabwe, and South Africa to examine whether the host range expansion patterns shared by the Ethiopian and the southern African populations of B. fusca have evolved independently. Base-pair differences in the cytochrome oxidase I (COI) gene were used to characterize haplotype diversity and phylogenetic relationships. There were seven haplotypes among the 30 sequenced individuals collected on four host plant species from 17 localities in the four countries. Of the seven COI haplotypes identified, the two major ones occurred in both sugarcane and maize. Genetic analyses revealed no detectable genetic differentiation between southern African B. fusca populations from maize and sugarcane (FST = 0.019; P = 0.24). However, there was strong evidence of variation in genetic composition between populations of the pest from different geographic regions (FST = 0.948; P < 0.001). The main implication of these findings is that the B. fusca populations in maize in southern Africa are more likely to shift to sugarcane, suggesting that ecological opportunity is an important factor in host plant range expansion by a pest.

The first report of resistance of the maize stem borer [Busseola fusca (Fuller)] to Bt maize (MON810) was made in the Christiana area of South Africa during 2007. The objective of this study was to evaluate the status of resistance of other populations of B. fusca to Bt maize. One greenhouse and two laboratory studies were conducted. B. fusca populations were collected on Bt maize as well as the adjacent refugia (conventional maize and non-Bt maize) in the Vaalharts area, 50 km from the Christiana site. Control populations were collected from sites where Bt maize was not planted. In the greenhouse study 720 potted plants were each artificially infested with 10 neonate larvae of the F1-generation after the field collected populations were reared through to adults. Numbers of live larvae and larval mass per plant were determined at regular intervals over a 35-d period. Larvae of the Christiana conventional population (Bt-susceptible) on Bt maize (CHR08ConBt) and Bethal conventional population (Bt-s...

The lepidopteran stemborers Busseola fusca (Fuller) (Lepidoptera: Noctuidae), Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) are effectively controlled by Bt maize that expresses the Cry1Ab insecticidal protein. Another noctuid species, the cutworm Agrotis segetum (Denis and Schiffermüller) (Lepidoptera: Noctuidae), which is the most common and injurious pest of maize seedlings in South Africa, is exposed to Bt toxin for a part of its life cycle. The effect of this exposure to Bt maize has not been studied yet. The aims of this study were to determine the effects of Bt maize (events MON810 and Bt11) on larval mass, development time, survival, and fecundity of A. segetum. Laboratory studies were conducted with first- and fourth-instar larvae and moths. Results showed that the effect of Cry1Ab toxin on the biology of A. segetum larvae and moths were largely insignificant. The effects of the two Bt maize events on the different parameters measured in this study was not similar between the Bt events and their respective iso-hybrids. Compared with larvae that fed on conventional (non-Bt) maize, Bt maize did not affect survival of first-instar larvae. However, mean mass of larvae that fed on Bt maize (Bt11) was significantly lower. Feeding on Bt maize did not have a significant effect on development and survival of fourth-instar larvae or moth longevity. It did, however, delay the development period to pupa formation. Fewer eggs were laid by moths fed as larvae on maize event Bt11 compared with MON810. This study indicates that Bt maize will most likely not have any significant effect on the control of A. segetum under field conditions.

Scelionid egg parasitoids of Telenomus spp. have been shown to significantly affect noctuid stemborer populations and yields of maize in western Africa. One of them, T. isis, has never been reported from eastern Africa and was introduced into the laboratories of the International Centre of Insect Physiology and Ecology, Kenya. This study evaluates the biotic potential of T. isis using East African stemborers as hosts. Host acceptance was tested using 15 lepidopteran borer species. Only noctuid stemborers were accepted for oviposition by T. isis. Sesamia calamistis Hampson, Sesamia nonagrioides (Lefebvre), and Busseola fusca (Fuller) were further used to study the effect of host species, host age, duration of host deprivation, temperature, and humidity on the performance of the parasitoid. In contrast to sex ratio, developmental time, parasitism, and parasitoid emergence varied significantly with host species, and the former two decreased with the age of host eggs. Female longevity increased with duration of host deprivation, whereas average lifetime fecundity decreased, probably because of oocyte resorption. T. isis successfully developed between 18 and 32 degrees C at both low (40-50%) and high (70-80%) relative humidity regimens, but temperature played a more critical role. Using the modified Logan model, the lower and upper temperature thresholds for development were estimated at 11.5 and 37.5 degrees C, respectively, with an optimum at 30.5 degrees C for both humidity regimens. Depending on temperature and relative humidity regimen, the intrinsic rate of increase (r(m)) varied from 0.077 to 0.300, net reproductive rate (R(o)) from 7.70 to 83.96, and generation time (G) from 11 to 38 d. The results of this study indicate that T. isis is likely to establish in eastern Africa.

During the dry season in the humid forest zone of Cameroon, maize is the most important off-season cash crop grown in hydromorphic inland valleys (IVs), which may also be reservoirs for pests such as the stemborer Busseola fusca Fuller and its natural enemies. Pest and parasitoids were monitored in IVs and close-by upland maize fields from January 2002 through December 2004. Trap catches and oviposition data showed that B. fusca was active throughout the dry season and long and short rainy seasons of 2004. Egg batch densities were considerably lower in the dry than in the rainy seasons. Important natural enemies were the scelionid egg parasitoids Telenomus busseolae Gahan and T. isis Polaszek. B. fusca was the predominant borer species in all seasons in maize in IVs as well as in upland fields, followed by Sesamia calamistis Hampson and Eldana saccharina Walker. B. fusca larval densities were lowest in the IVs and increased in the course of the year in the upland fields. In contrast, S. calamistis densities were higher in IVs than in upland maize fields. At harvest of the IV maize, B. fusca and E. saccharina larval densities were 47.3 and 15.5 times higher, respectively, than on old maize stubbles in upland fields planted during the previous year. Grain yields as well as the marketable ear index were 1.1–2 times higher in the dry season than in the long and short rainy seasons, indicating the importance of IVs for dry season maize production in Cameroon.

Cotesia sesamiae (Cameron) is an indigenous larval endoparasitoid that attacks mid- to late-stage gramineous stem borer larvae in Africa. Two biotypes of C. sesamiae have been reported with differential abilities to suppress the immune system of Busseola fusca Fuller. Eggs of a C. sesamiae population from Mombasa were encapsulated, whereas eggs of a population from Kitale were not. Total and differential hemocytes were counted in larvae of B. fusca at six times (2 h, 14 h, 24 h, 72 h, 120 h, 168 h) after being exposed to parasitoids from Kitale and Mombasa. The total numbers of hemocytes in a larva parasitized by the C. sesamiae population from Mombasa were higher as compared with larvae parasitized by the C. sesamiae population from Kitale. Plasmatocytes, in particular, were reduced in larvae parasitized by C. sesamiae from western Kenya from 72 to 168 h after oviposition. Our results suggest that plasmatocytes probably play an important role in the immune response of B. fusca. Significant proportions of the host larvae were still at the larval stage for those parasitized by C. sesamiae from Mombasa and another species of Cotesia, Cotesia flavipes Cameron at day 12. A reduction of B. fusca larval weight was observed on day 12 after oviposition by C. sesamiae from Kitale.

The effect of vegetation, intercropping, and Telenomus spp. egg parasitism during the vegetative stage of maize on Busseola fusca (Fuller) (Lepitoptera: Noctuidae) infestations and maize yields at harvest were studied during two consecutive cropping seasons, in the humid forest zone of Cameroon. Six locations grouped into three blocks, representing gradients in human population densities of 15–88 inhabitants/km2 were chosen. The fields were located at 20–90 min walking distance from the next road. Differences between blocks in the measured variables were mostly not significant indicating that the population density gradient was not strong enough to affect length of fallow period and thereby vegetation, the population dynamics of pests and natural enemies, and maize yields in forest fields. Numbers of egg batches per plant but also egg parasitism by and sex ratio of Telenomus spp. were significantly higher during the second than the first season (66.9 versus 19.9% and 0.67 versus 0.21, respectively). As a result, the number of borers per plant was only 0.22 versus 0.73 during the first season. Similarly, total mortality of immature B. fusca was 60.5% during the first and 93.2% during the second season. The seasonal differences in unexplained mortality was probably because rainfall caused drowning of migrating first instars. High mean parasitoid mortality at the beginning of the first season was probably caused by high superparasitism promoted by low host density conditions. Across seasons, abundance of grasses in the surroundings of a field was negatively related to egg batch density. Likewise, numbers of B. fusca decreased with increasing density of the nonhost cassava in the field, indicating increasing mortality of migrating larvae. Egg numbers per plant was negatively and egg parasitism or parasitoid sex ratio was positively related to yield.

Eight insecticide experiments were conducted in 7 localities of Cote d'Ivoire to study the feasibility of developing a reliable model of crop losses of maize caused by stem borers based on damage assessment during the growing cycle. The observed damage was the percentage of tunneled internodes and the percentage of dead-hearts 80 d after seedling emergence. Five trials were used to fit the model; the remaining 3 were used to validate it. Sampling throughout the growing cycle revealed that only 2 borer species were involved: Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Eldana saccharina Walker (Lepidoptera: Pyralidae). Dead-hearts were mainly caused by the 1st species, whereas the tunneled internodes resulted from the presence of both pests. The model, which is aimed at estimating crop losses after damage has occurred, explained 81% of the variation in yield. The validation study showed that the model enabled a prediction of yield within a range of approximately ±10% at different localities and under different infestation conditions.

A surrogate stem made of wax paper elicited optimum ovipositional response from Busseola fusca (Fuller). It closely resembled a maize stem with intact leafs heaths, which provided physical stimuli necessary for B. fusca egg laying, and facilitated quick recovery of eggs. B. fusca females readily inserted their ovipositors into spaces between the surrogate stem and leafsheaths and laid eggs in linear rows. In both choice or no-choice ovipositional tests, gravid females laid equal or higher numbers of eggs on the surrogate stems than on susceptible INB-A maize stems. The method has facilitated the mass rearing of B. fusca and bioassays of plant allelochemicals to the insect ovipositional response.

Since the appearance of the stem borer Chilo partellus (Swinhoe) on the African continent in 1932, it has continuously expanded its distribution in the warm, low-altitude regions of eastern and southern Africa. The current study revealed that C. partellus is expanding its distribution into the high elevations of the eastern Highveld region of South Africa. The only stem borer already found there (elevation 1,600 m) is Busseola fusca (Fuller). After C. partellus invaded the region, it rapidly increased its share of the total borer population every year. On maize, it reached 32% of the total borer population within 6 yr and on grain sorghum 59% within 7 yr. The most rapid population increase by C. partellus occurred on the ratoon grain sorghum crop. Within 2 yr it became the predominant borer, constituting ≈90% of the total stem borer population. C. partellus has proven to be an efficient colonizer, and it seems to be displacing the indigenous B. fusca. C. partellus survives the dry winters (at subzero temperatures) of the Highveld region in South Africa by diapausing low in the dry stalks, often beneath the soil. Hibernating larval populations of C. partellus terminate diapause and emerge as moths ≈1 mo earlier than B. fusca . This enables C. partellus to infest the grain sorghum ratoon crop before B. fusca , thus becoming the predominant borer in this niche. The life cycle of C. partellus is 3 wk shorter than that of B. fusca , which gives it a further competitive advantage because of its higher potential rate of increase.

Six experiments were conducted in the savanna and forest areas of Côte d'Ivoire to study the influence of stem borers on maize crop yield components and production. Statistical models showed the effect of the oldest preimaginal instars of 2 stem borers, #Eldana saccharina$ Walker (#Pyralidae$) and #Busseola fusca$ (Fuller) (#Noctuidae$). Plant destruction was mainly caused by early attack of #B. fusca$. Attack by both borers on or about the 60th d alter emergence induced plant sterility. Stem borers had no direct effect on number of grains per cob-carrying plant : the level of this yield component was set according to the level of the previously determined components through a compensation phenomenon. The last yield component, average weight of grain, decreased with attack by #E. saccharina$ occurring on or about the 80th d after emergence. Effects of borer aggregation, maize variety, and maize streak virus incidence were studied. The statistical model of crop loss, which explains 81.7% of the variation in yield, was validated from the results of 3 trials that were not included in the regression analysis. It enables one to estimate accurately crop losses in most of Côte d'Ivoire with only 2 samplings during the growing season, on the 40th and 80th d after emergence. (Résumé d'auteur)

Two parental maize ( Zea mays L.) lines, a susceptible inbred ‘Inbred A’ and a resistant inbred ‘Mp704’, were evaluated along with their F 1 hybrids, ‘Mp704’ × ‘Inbred A’ and ‘Inbred-A’ × ‘Mp704’, for resistance to Chilo partellus (Swinhoe) and Busseola Fusca Fuller in a screenhouse. Factors reducing oviposition on ‘Mp 704’ in choice tests were not manifested in the one F1 hybrid tested. However, the antibiosis mode of resistance operating within the resistant parent ‘Mp704’ was generally expressed in the F1 hybrids. The resistant parent and the F1 hybrids showed significantly lower foliar damage ratings as well as stem damage than the susceptible parent against both stem borers under artificial infestation. Larval survival on the F1 hybrids was as low as on ‘Mp704’. As measured by nutritional indices, poor food utilization but high relative consumption rate on resistant ‘Mp704’ and low consumption rate but high food utilization on F1 hybrids resulted in slow development and low biomass gained by C. partellus and B. fusca on these cultivars.

The effect of temperature, photoperiod, artificial diet, and water on the termination of diapause by larvae of the African maize stem borer, Busseola fusca (Fuller), was studied in the laboratory. Diapause termination as indicated by pupation was accelerated at 26°C and was slower at 23 and 28°C. Complete darkness did not prevent diapausing larvae from pupating, and long days accelerated pupation. Lack of food or water did not prevent pupation, but the survival rate of the diapausing larvae was low. The provision of artificial diet or water accelerated the emergence from diapause. At 26°C, a photoperiod regime of 16:8 (L:D) h, and adequate water, B. fusca larvae terminated diapause after 34 d. It was concluded that a combination of temperature and photoperiod played an important role in completion of diapause development in B. fusca , and water was important only as a stimulus for morphogenesis following diapause.

During diapause, larvae of the stem borers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) progressively decreased in weight at the rate of 8.7 and 4.6 mg per week, respectively. Larvae lost 50% of their initial body mass and had up to seven stationary molts. Larvae became lessactive and lost pigmentation. The longer the larvae remained in diapause, the lighter in weight the emerging moths were, with fewer eggs and oocytes. After 8 mo in diapause, the emerging moths weighed about half as much and had about half as many eggs and oocytes as moths that emerged from nondiapausing larvae.

The distribution of maize stem borers, Busseola fusca Fuller, Sesamia calamistis Hampson, and S. penniseti Bowden, throughout south-western Nigeria was studied between November and December 1964. The maize-sample survey revealed that B. fusca was more abundant than S. calamistis . While B. fusca was prevalent in the southerly, more humid lowland rainforest zones, S. calamistis was generally distributed and was more prevalent in the dry savanna zones of the region. S. penniseti was not abundant and was very sparsely distributed. There was a marked difference in the position of egg masses on the maize plants. All egg masses of B. fusca were laid within 30 inches of the maize whorl, while S. calamistis egg masses were spread over greater distances from the whorl. This distribution appears to be associated with the larval habits of both B. fusea and S. calamistis . Larval populations studies revealed that in lbadan (and probably south-western Nigeria) there are 4 generations of B. fusca in maize per annum. There are 2 generations between April and July, 1 in September-October, and another in November. It is the larvae of the November generation which go into the dry-season diapause and which later give rise to the 1st-generation adults the following year. S. calamistis ,, although not so numerous as B. fusca , was observed to breed throughout the year.

Diapausing larvae of Busseola fusca (Fuller) occur throughout most of the year, even when maize is actively growing. Diapause was recorded in June, reached the peak in July, and completed in September. The least number of larvae was obtained in October. There was a buildup again of diapausing larvae from November, with the peak in December. Diapause development in the November-December generation was completed about february-March of the following year. The fact that some of the larvae of B. fusca go into diapause at each generation, irrespective of the state of the maize plants, suggests a probable genetic mechanism or heredity. Some morphological and physiological factors such as coloration, molting frequency, loss in weight, and feeding activities associated with diapause in the insect were studied. Pigmented (nondiapausing) larvae of B. fusca occurrcd most abundantly when maize plants were either young or mature but still fresh, while the nonpigmented (diapausing larvae) occurred at those times of the year when the maize stems were dry in the field. Most of the larvae collected in October and November were pigmented; only 11.6% collected in October and 43.6% collected in November were diapausing larvae. Therefore, diapause may not, after all, be responsible for the coloration of the larvae of B. fusca . Diapausing larvae of B. fusca molted up to 6 times during the period of diapause and progressively decreased in weight at the rate of 7.4 mg/week. Diapausing larvae of B. tusca fed throughout the period of diapause, but the rate of feeding activity (when compared with the nondiapausing individuals) was reduced by about 82%. The alimentary canal, though flaccid, was never empty. Water docs not terminate diapause in the field but rather enhances the emergence of moths from maize stubble after diapause development has been completed.

Emergence of moths of Busseola fusca Fuller and Sesamia calamistis Hampson was influenced by the onset of darkness. Most of these moths emerged at about 7 pm, nearly an hour after sunset, and continued until about 10 pm. Copulation appeared to induce female stemborer moths to oviposit readily, uniformly, and within a few days. Unmated moths laid fewer eggs, and these erratically. Copulation of unmated females after a period of up to 4 days after emergence did not significantly affect the fecundity of females. In both B. fusca and S. calamistis there was only a slight difference between the longevity of the unmated male and female moths. Mated moths, especially the females, had a shorter life span, probably because of activities involved in mating and oviposition.

A cheap pistol-grip sprayer holding 500 ml insecticide and designed to apply 1 ml/sorghum whorl at each stroke in order to control larvae of Busseola fusca (Fuller) was evaluated in field tests in Nigeria. By making a simple adjustment, the sprayer could apply either a thin jet stream or a cone-shaped spray. Application of an 85% wettable powder of carbaryl at a rate equivalent to 0.16 lb/acre (4 g formulation/sprayer) gave satisfactory control (78%) of young second-generation larvae; sprays were more effective than jet streams

The effect of varying populations of Busseola fusca Fuller larvae on the growth and yield of maize ( Zea mays ) was studied in Ibadan (western Nigeria) in 1964. Plants averaging between 18 and 24 inches tall were manually infested with newly hatched larvae. In terms of increases in height and number of leaves, the rate of plant growth decreased as the number of borers applied increased. The percentage of “dead hearts” increased as the number of borers per plant increased. Infestation also affected both the yield and quality of the cobs (ears) produced. One or 2 borer larvae per plant reduced the yield by as much as 25%.