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The noctuid stem borer Busseola fusca is an important pest of maize and sorghum in Sub-Saharan Africa. The presence of this species occurred mostly on cultivated than on wild habitats. Busseola fusca is oligophagous having a narrow range of a wild grass species. This might be due, in part, to differences in silicon (Si) content in plant tissues between cultivated and wild grasses. In the present study, we have tested this hypothesis by studying the survival and the relative growth rate (RGR) expressed as daily weight gains of B. fusca larvae on maize and six wild host plants, mostly present in the natural habitat where B. fusca occurred, and correlated with their Si contents. Survival and RGR of B. fusca larvae were considerably higher on maize and wild sorghum than on the other grass species, and they were negatively related to plant Si content. This was corroborated with results on RGR from artificial diets amended with increasing levels of Si. In addition, if Si was added to maize growing substrate B. fusca larval growth was significantly reduced confirming the involvement of Si in B. fusca larvae – Poaceae interactions. The results provide insight into the possible mechanisms of oligophagy of B. fusca and provide a correlative support for a physical role of plant endogenous Si in impeding feeding of B. fusca larvae.

The effect of temperature on the reproduction and development of Busseola fusca was studied under laboratory conditions. Single male–female pairs were confined to oviposition chambers kept at 15, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. Data on reproduction parameters were captured daily. Oviposition occurred at all the mentioned temperatures but no fertility was recorded at 30°C. The total number of eggs laid per female moth was between 300 and 400 and the optimum temperature for oviposition and fertility was between 20 and 26°C. Larval development was studied at five different temperature regimes, i.e. 15, 18, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. The most favourable temperature as well as the upper threshold temperature for larval development was between 26 and 30°C. Total development period was 152.6–52.6 days, respectively, at 15°C, and 26–30°C. The thermal constants for B. fusca was 99.50, 536.48, 246.25 and 893.66°D and lower temperature thresholds were 10.36, 8.14, 8.99 and 8.84°C, for completion of the egg, larval, pupal and egg-to-adult stages, respectively. Results on the thermal constants and lower and upper threshold temperatures of B. fusca can be used to predict the impact of climate change on the distribution and population growth of this pest.

Recent studies show that Vetiver grass, (Vetiveria zizanioides (L.) Nash), may have potential as a dead-end trap crop in an overall habitat management strategy for the spotted stem borer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). Vetiver grass is highly preferred for oviposition, in spite of the fact that larval survival is extremely low on this grass. The oviposition behaviour of female Chilo partellus moths was investigated by determining the amount and size of egg batches allocated to maize and Vetiver plants and studying the effect of rearing conditions and oviposition experience on host plant selection. Two-choice preference tests were used to examine the effect of experience of maize (a suitable host plant) and Vetiver plants on the oviposition choice of C. partellus. For both field-collected and laboratory-reared moths, no significant differences were found in the preference distributions between the experienced groups. It is concluded that females do not learn, i.e. that they do not change their preference for Vetiver grass after having experienced oviposition on either maize or this grass, which supports the idea that trap cropping could have potential as a control method for C. partellus. Differences observed between field-collected and laboratory-reared moths in the amount and size of egg batches laid on maize and Vetiver grass indicate that data obtained from experiments with laboratory-reared insects should be treated with caution.

Sites in the humid forest of Cameroon and the derived savanna of Benin were selected to evaluate the effect of planting border rows of wild host plants on lepidopterous stem-borer infestations and on maize yield. Grass species were chosen that in surveys and greenhouse trials were highly attractive to ovipositing female moths but with offspring mortality of close to 100%, thus acting as trap plants. In Cameroon, elephant grass Pennisetum purpureum Moench significantly lowered infestations of Busseola fusca (Fuller), Sesamia calamistis Hampson and Eldana saccharina Walker and increased yields of maize though the differences were not significant during all three cropping seasons. In 1998 in Benin, the only grass tested, Pennisetum polystachion L., significantly increased parasitism of mainly S. calamistis eggs by Telenomus spp. and larvae by Cotesia sesamiae Cameron and reduced numbers of the cob-borer Mussidia nigrivenella Ragonot. In 1999, three grass species; P. polystachion, Sorghum arundinaceum (Desv.) Stapf and Panicum maximum Jacq. were tested. Panicum maximum was the most efficient species for suppressing S. calamistis and M. nigrivenella infestations and enhancing egg and larval parasitism. In the Benin trials, with the exception of M. nigrivenella damage to cobs, the grass species tested had no beneficial effect on yield because pest densities were too low and also rodent damage to maize was enhanced with grasses in the vicinity of the crop. By contrast, stand losses due to Fusarium verticillioides Sacc. (Nirenberg), were significantly reduced by border rows of grasses.

Studies on the lepidopterous stem borer, Busseola fusca (Fuller) and its major larval parasitoid, Dolichogenidea fuscivora Walker were carried out in the field and the laboratory in eastern Ethiopia. Larvae of B. fusca are also parasitized in the field by the braconid, Bracon sesamiae Cameron and the sarcophagid, Sarcophaga sp., but in low numbers. Parasitism of B. fusca by D. fuscivora is as high as 71% during the dry season (November-March) and approximately 18% in the wet season (June-September). Dolichogenidea fuscivora is active throughout the year. In the laboratory it requires nearly 26 days at 24 ± 1°C to complete the development of one generation (egg to egg laying). Longevity of adults is affected by the availability of food and water. Mating and oviposition reduced the life spans of males and females, respectively. Sixty five to 75 larvae emerged from eggs laid by a single female. The sex ratio ranged from 1:1 to 7:1 (female:male), the average being 5:1.

Eighteen parasitoids were recorded from the African stem borer, Busseola fusca (Fuller), on maize and grain sorghum, in Delmas and Cedara, South Africa. In Delmas, larval parasitism on both crops fluctuated below 20% with occasional peaks of 40–60%. In Cedara, larval parasitoids were active throughout the season with peaks of 75% and 60% parasitism during January and March-April, respectively on the ratoon crop, and 20% in May on the crop. Pupal parasitism peaked in Cedara at 100% during February-March, and at 80% during November, when parasitoids attacked pupae that formed after B. fusca larvae had emerged from diapause and pupated. In Delmas activity by pupal parasitoids was negligible. The egg parasitoids, Telenomus busseolae Gahan (Hymenoptera: Scelionidae) and Trichogrammatoidea lutea Girault (Hymenoptera: Trichogrammatidae), were rare. The larval parasitoid, Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae), was active throughout the season and was by far the most abundant, emerging from about 90% of parasitized larvae. Its cocoons were often attacked by Aphanogmus fijiensis (Ferrière) (Hymenoptera: Ceraphronidae). Second in abundance among the larval parasitoids was Bracon sesamiae Cameron (Braconidae) whose cocoons were attacked in turn by Eurytoma braconidis Ferrière (Hymenoptera: Eurytomidae). Eurytoma braconidis was reared also from cocoons of Euvipio sp. and Aleiodes sp. (both Braconidae). All other larval parasitoids were rare. Procerochasmias nigromaculatus (Cameron) (Hymenoptera: Ichneumonidae) was the most abundant pupal parasitoid. Trichogrammatoidea lutea, Glyptapanteles maculitarsis (Cameron) (Braconidae) and Odontepyris transvaalensis (De Buysson) (Hymenoptera: Bethylidae) have not been recorded before from B. fusca. Some considerations and proposals for introductions of parasitoids into South Africa against B. fusca are discussed.

The comparative influence of Busseola fusca (Fuller) and Chilo partellus (Swinhoe), both as separate and mixed populations, on growth and yield of grain sorghum was investigated in a field experiment, using an artificial infestation in cages. C. partellus was more injurious than B. fusca as indicated by whorl damage, stalk injury and yield loss. In the case of mixed populations, dispersion of larvae and damage were independent of B. fusca numbers. A regression equation, Logit Y = 0.24 + 2.06 logit x, relating visible plant damage to yield loss was determined. Control strategies in the case of mixed stem borer populations should be directed against C. partellus.

The distribution and species composition of lepidopterous maize borers was studied in six locations in southern Nigeria during the second planting season (August-November) of 1985 and 1986. Sesamia calamistis Hampson (Noctuidae) and Eldana saccharina Walker (Pyralidae) were the stem borers most abundantly found in the locations sampled. S. calamistis was the dominant species up to eight weeks after planting in all locations. E. saccharina was the most abundant species from nine weeks after planting onwards, except at Umuahia where S. calamistis always comprised over 50% of the borer population. Mussidia nigrivenella Ragonot (Pyralidae) was found attacking maize ears in all locations, while Busseola fusca Fuller (Noctuidae) was found only at Idah and Alabata, and even there constituted only a small proportion of the population. Other borer species found were Coniesta (= Acigona) ignefusalis (Hampson) (Pyralidae) and Cryptophlebia species (Olethreutidae).

This study was conducted in the humid forest zone of Cameroon, in 2002 and 2003. The main objective was to investigate the effects of intercropping on infestation levels and parasitism of the noctuid maize stem borer Busseola fusca Fuller. Two trials were planted per year, one during the long and one during the short rainy season. Maize monocrops were compared with maize/legume or maize/cassava intercrops in two spatial arrangements: maize on alternate hills or in alternate rows. Spatial analyses showed that the stemborer egg batches were regularly dispersed in the maize monocrop and aggregated in the intercrops, as indicated by b, the index of dispersion of Taylor's power law. Depending on the crop association and planting pattern, intercrops reduced the percentage of plants with stem borer eggs by 47.4–58.4% and egg densities by 41.2–54.5% compared to monocropped maize. Consequently, larval densities were 44.4–61.5% lower in intercrops compared to monocrops. Intercropping maize with non-host plants did not affect larval parasitism. Up to two-fold higher levels of egg parasitism by scelionid Telenomus spp. were recorded in inter- compared to monocrops during the short rainy seasons of 2002 and 2003. No differences were found among the mixed cropping treatments and parasitism was lower during the long compared to the short rainy seasons. It was proposed that differences in levels of parasitism were due to density dependence effects rather than the effect of the presence of non-host plants in the system.

Three lepidopteran cereal stemborers, Chilo partellus (Swinhoe) (Crambidae), Busseola fusca Fuller, and Sesamia calamistis Hampson (Noctuidae) were collected from maize and sorghum in Ethiopia. The noctuid stemborers are indigenous to Africa while C. partellus is an introduced species from Asia. In 1999, the Asian stemborer parasitoid, Cotesia flavipes Cameron (Braconidae) was found to be widespread in Ethiopia, even though it had never been released in the country. In addition to attacking Chilo partellus, Cotesia flavipes was reared from B. fusca and S. calamistis. The origin of C. flavipes in Ethiopia may have been Somalia where it was released in 1997 near the border with eastern Ethiopia. Percent parasitism of borers by C. flavipes was higher in eastern Ethiopia than other surveyed regions, and parasitism was higher in 2000 than 1999. Parasitism was higher when cereals were intercropped with other plants and when wild grass hosts of stemborers were present.

New information on the intraseasonal progression of larval infestations of Busseola fusca (Fuller) in South Africa was obtained through repeated sampling in maize plantings of different planting dates over various seasons. Due to the occurrence of distinct periods of moth flight, variation in planting date had a marked influence on levels of larval infestation. Also, plants were found to be most attractive as sites for oviposition between three and five weeks after emergence, resulting in a definite pattern in the time distribution of different larval instars in different plant parts. In the pre-tassel stage of plant development, most larvae occurred in localized groups within the whorls, reaching maximum numbers eight weeks after plant emergence. The emergence of the tassel forced some larvae to migrate to adjacent plants, resulting in an increase of internally damaged plants without an increase in larval numbers. It is shown that scouting for eggs over a limited period of plant development can lead to better timing of spray applications and thus to more cost-effective control measures.

Through repeated sampling in maize planted on different dates over different seasons in South Africa, it was shown that damage by Busseola fusca (Fuller) to plant parts other than the whorl had an important influence on yield. Damage to plants in the period after tasselling was shown to be important. The number of larvae in the plant was a weak estimator of expected yield losses.

All available records showed that Eldana saceharina Wlk. occurs in wild plants in all suitable areas of Africa south of the Sahara. Until a few years ago, it was only of economic importance in West Africa as an occasional pest of maize and sugar-cane, but a crop-feeding form has recently appeared in East Africa. Biological studies were carried out in the field and laboratory at Kawanda, Uganda, between 1970 and 1972 using natural and artificial larval diets. The life-cycle lasted 2–3 months, depending on temperature, and the number of larval instars depended partly on the diet. The adults lived for two weeks, during which time the females each laid 400–600 eggs. The majority of eggs and small larvae were taken by ants, but sufficient larvae survived to cause considerable damage. The pupae and larger larvae lacked efficient natural enemies in East Africa, and the introduction of parasites is suggested to prevent serious crop damage. The relatively evenly spread rainfall at Kawanda allowed maize to be planted every month so that field populations of E. saccharina and the other stem-borers Chilo partellus (Swinh.), Busseola fusca (Fuller) and Sesamia calamistis Hmps. could be studied throughout the year. Collections from maize, sorghum and sugar-cane showed that, although the four species attack the same host-plants, they occupy different ecological niches.

Research on Lepidopterous stem borers of Nigerian cereals began in 1951. Preliminary surveys finished in 1954 and from 1955 to 1961 the author studied these pests in Northern and Western Nigeria.Guineacorn (Sorghum vulgare) and millet (Pennisetum typhoides) are the most important cereal crops in Northern Nigeria, and maize (Zea mays) is the only cereal of any importance in Western Nigeria. The crops are sown early in the wet season, which alternates with a dry season of two to seven months, and mature in three to five months. They are cultivated by hand and few farmers grow more than one acre of any one cereal.The host ranges of all the known species of Nigerian cereal stem borers (viz., Busseola fusca (Fuller), Sesamia calamistis Hmps., S. penniseti Tams & Bowden, S. poephaga Tarns & Bowden, S. nonagrioides botanephaga Tams & Bowden, Manga basilinea Bowden, Coniesta ignefusalis (Hmps.), Chilotraea sp. ? argyrolepia (Hmps.), Chilo sp. ? phaeosema, Martin, Maliarpha separatella Rag. and Eldana saccharina Wlk.) are summarised and their distribution in Nigeria and relative importance there are discussed.B. fusca and Coniesta ignefusalis are the most important stem borers of guineacorn and millet, respectively, and detailed accounts of their life-cycles and seasonal cycles are given, together with observations on adult activity, light-trap catches, larval migration, larval morphology and the effects of larval feeding patterns on plants of guineacorn and millet. Differences between the pupae of the three Noctuid genera (Busseola, Sesamia, Manga) and all stages of C. ignefusalis are illustrated. Some information on the biology of S. calamistis, S. poephaga and M. basilinea is also given.At Samaru, the life-cycles of B. fusca and G. ignefusalis are completed in about two months under field conditions and in the absence of diapause. Three generations develop during the growing season, larvae of the third entering diapause until the next season. Many diapause larvae survive the dry season in crop residues, and the local practice of stacking stems for later use in building, etc., ensures reinfestation of subsequent crops, particularly near villages. The diapause ends between late April and early June, so that adults of the diapause generation emerge about three weeks after millet and guineacorn have germinated. Experiments indicate that diapause is terminated when larvae are provided with moist food or drink water. The relative abundance of B. fusca and C. ignefusalis in guineacorn, millet and maize largely reflects host selection by ovipositing females. C. ignefusalis lays freely only on millet and is therefore mainly confined to this crop, whereas B. fusca, though favouring guineacorn, also lays on the other two crops. Experiments indicate that more eggs are laid on larger plants.Early millet and maize are harvested before borer populations reach their highest level. Guineacorn tolerates the considerable damage done by the high populations present at the end of the season but late millet and second-crop maize do not. Any factor hindering normal crop development tends to increase the damage done.A provisional list of 14 primary parasites, three hyperparasites, one predator and four diseases is given. Tetrastichus atriclavus Wtstn., Apanteles sesamiae Cam., and Pediobius furvus (Gah.) were always present on B. fusca at the end of the season. Syzeuctus sp. was the most important parasite of C. ignefusalis and was regularly reared from diapause larvae, and other common parasites of this species later in the season were Sturmiopsis parasitica (Curran), T. atriclavus and Hyperchalcidia soudanensis Steffan. The over-all rate of parasitism seldom exceeded 10 per cent, of all larvae and pupae collected. Bacillus thuringiensis killed many diapause larvae of B. fusca and was the most important disease recorded.The results of experiments relating yields to stem-borer attack in maize, early millet, late millet and guineacorn are presented and discussed. Early-sown maize suffers little damage but second-crop maize at Ibadan suffers losses of stand which, in local farms, generally exceed 20 per cent. In experiments, loss of stand did not always result in loss of yield, and evidence is presented that, under certain conditions, loss of stand is compensated for by the production of heavier cobs. At Samaru, the development of single larvae of B. fusca in otherwise healthy stems reduced their yielding capacity by 28 per cent, of the mean cob weight of healthy stems (P In six experiments on early millet, little reduction in yield occurred, even when infestations were much higher than those normally experienced, but late millet suffered almost complete loss of yield in two experiments and more than 90 per cent, of the stems were bored in. two other experiments, in which yields were low. These results and general observations indicate that stem borers, particularly C. ignefusalis, play a major part in limiting yields of late millet.In six experiments on guineacorn, significantly so in three of them, the yield per bored stem was higher than that per unbored stem, and it appears that borers concentrated on or were concentrated on the larger, higher-yielding stems, possibly as a result of selective oviposition. In one other experiment, stems bored by first-generation larvae yielded significantly less than unbored stems but neither in this nor in any other experiment was over-all borer attack related to a reduction in yield and it is generally true that excellent yields of guineacorn can be obtained in the presence of high populations of borers.Reduction of the carry over of diapause larvae, by destroying or composting crop residues or removing them from the field, has given good control on the experimental farms at Samaru but it is difficult to extend these measures to local farms. Farmers should clean up their fields before the beginning of the rains and stems that are to be used for building should be exposed in the open during the dry season; to reduce populations of diapause larvae. Insecticidal control has as yet shown little promise and plant breeding for resistance has not begun.The necessity for further work to confirm the general conclusions drawn here is stressed and possible lines of investigation are indicated.

The life-history and seasonal cycle of the Lepidopterous borer, Busseola fusca (Fuller), the most serious pest of maize in Southern Rhodesia, have been studied there.There are two generations in the year, the majority of the full-grown larvae of the second entering diapause, in which condition the dry season is passed in the maize stem, but a proportion of the second-generation consists of short-cycle individuals that give rise to moths irregularly during the dry season.In the field, the egg stage lasts about 7–11 days, according to the time of year. In the laboratory, there are six, very occasionally seven, larval instars in the first generation, occupying about 37 days, and the pupal stage lasts about 17 days. In the second (diapausing) generation there may be one or two additional moults without appreciable change in size, and there is considerable variation in the length of instars and in the date of entry into diapause, but by mid-June the bulk of the larvae that will survive are in diapause. The majority of diapause larvae pupate in early November, the pupal stage lasting about 23 days.The feeding habits of the larvae are described and reference is made to other food-plants.The length of life of the adult, in cage conditions, averages 6–7 days, but there is great variation. When provided with diluted honey, adults were not observed to feed, and absence of such food did not appear to impair egg-laying. The sex ratio was 1:1, but in catches at a light-trap the ratio of males to females was 5:1. Copulation takes place shortly after emergence, and oviposition may begin within 24 hours of emergence.The average number of eggs laid per female in cages was 360 over an average of four days, one female laying 1,032. Several batches of eggs may be laid in one night. A single mating appears to be sufficient, but males may copulate with more than one female. Eggs laid by virgin females do not hatch.Diapause is thought to be induced by larval feeding on drying food. Continuous rearing of non-diapause generations can be achieved by feeding the larvae on fresh, green maize. Similarly, in the field, irrigated out-of-season maize will support non-diapause generations and constitute a source of infestation that may render ineffectual the normal routine destruction of all plants of the previous dry-land farming season.The main parasite is the Tachinid, Sturmiopsis parasitica (Curr.), which may destroy more than 33 per cent, of the larvae in either generation.

1. Apanteles sesamiae, Cam., is the only parasite of Busseola fusca, Fuller, which is of importance in the Eastern Transvaal.2. The adult is described, and the morphology of the last stage larva of the parasite is discussed in detail.3. The biology and bionomics of the species are dealt with, and the effect of parasitism on the host is described.4. The extent of natural parasitism and the rapidity of increase in the field shows that A. sesamiae is an effective parasite of the Maize Stalk-borer in South Africa.5. The results of cold storage experiments are given and the methods of shipping parasite material are described. It was found impracticable to ship cocoons, but successful consignments of parasitised borer larvae were sent to Canada.

The larval populations of Busscola fusca (Fuller), a major pest of the guineacorn (Sorghum vulgare) crop, which survive the dry season in and around villages near the Research Station, Samaru, Northern Nigeria, were assessed by sampling. The larvae of B. fusca survive the five to six rainless months in diapause in crop residues, most important of which are guineacorn stems, which are stacked in the fields after harvest. Between 1956 and 1962, 100-stem random samples were collected from as many stacks as possible within an area of about six square miles. Each of the 348 samples was dissected immediately after collection and the number of living larvae of B. fusca per sample was recorded. The mean number of larvae per sample varied annually and ranged from 7 in the 1960–61 dry season to 33 in the 1959–60 dry season. The mortality of larvae is comparatively low between January and March, when most samples were collected, and it is concluded that the date of sampling did not unduly influence the estimates of annual variations of the population. The location of sampling areas also had surprisingly little effect and, despite uneven growth of the crop, the estimates of larval populations were remarkably uniform throughout the ten sampling areas and between samples within the main sampling area of Bomo village.It is concluded that there is considerable variation in dry-season populations from year to year. The factors causing this variation have not been determined, and it is suggested that other workers might profitably continue and expand these investigations.

Dentichasmias busseolae Heinr., an important pupal parasite of Pyralid graminaceous stem-borers in East Africa, is widely distributed in the Ethiopian Region but is more abundant in areas with an equatorial humid climate. In the laboratory adults mated immediately after emergence and started oviposition the same day. The female oviposits only in a borer pupa without a cocoon in a stem, and oviposition is stimulated by the presence of the frass of Chilo partellus (Swinh.) larvae. D. busseolae does not attack Busseola fusca (Fuller), Sesamia calamistis Hmps. or Eldana saccharina Wlk. in the field but these were accepted for oviposition when exposed in C. partellus pupation tunnels or with frass of C. partellus larvae, and were suitable for development. D. busseolae could complete its development in one- to eight-day-old C. partellus pupae when the pupal period of C. partellus was 10·5 days. The life-cycle was completed in 15–19 days at a mean temperature of 25°C, but could not be completed at a constant temperature of 30°C; temperatures fluctuating between 22°C and 30°C were not detrimental. At Namulonge (Uganda) percentage parasitism showed a positive correlation with rainfall, with a lag of about a month.

Trials in East Africa (chiefly in Tanganyika) are described to show that the time taken for first-instar larvae of Busseola fusca (Fuller) to reach the more closely packed young leaves in the central axis of the maize plant is about ten days, and that insecticides are effective up to the end of this period. Results show that the best time for control is as near hatching of the eggs as possible, but with more persistent insecticides such as endrin, economic control is possible up to five days later.A method of testing insecticides as residual deposits, by allowing first-instar larvae to walk on them, is given, and it was found that isodrin, DDT, endrin and γ BHC are highly effective as residual films. The MLD's for one minute in contact are 1·8 mg./sq.m. for isodrin, 4–7 mg. for DDT, 8·3 mg. for endrin and about 20 mg. for γ BHC. Derris emulsion has no residual effect after drying and is only effective in the liquid state after contact with larvae for several minutes.In a series of field trials over three years, increases in yield of up to 2·6 times the control yields were shown to be possible, and averaged twice the control yield. Endrin was the most consistently effective insecticide, applied as a 2 per cent, dust and as a 0·03–0·04 per cent, emulsion spray. Two applications of endrin at an interval of two weeks were effective, but, for DDT, three applications of an emulsion containing 0·05 per cent. DDT at nine-day intervals were more effective than two while one may be of little value. An application of 2·5 oz./acre of DDT can be effective for 7–10 days, while 1·5 oz./acre of endrin can be effective for 14 days. In general, however, rates per application should not fall below 3·5 oz. DDT or 2 oz. endrin per acre, overall.The superiority of a 5 per cent. DDT dust over one of 2·5 or 1 per cent, makes it more economical in a high-yielding, heavily attacked area. Diazinon and malathion in emulsion sprays are less persistent than DDT.Trials with 4 per cent, malathion dust and 0·15 per cent, malathion emulsion spray were inconclusive on account of heavy damage by Spodoptera sp.Attempts to increase the persistence of malathion and γ BHC by the addition of chlorinated terphenyl resins were also inconclusive, but DDT in emulsion, with resin, appeared more effective than DDT alone.The economics of successful control measures at the prices obtaining at the time are discussed under the various trials.Chemical estimations of the deposits of insecticides retained on the plants showed that between 1·4 and 3·7 per cent, of the quantity applied per unit area can be recovered in this way.In a discussion of the significance of the results in control, it is suggested that spraying the stems only is half as effective as spraying the whole plant.The conditions and results relating to two aerial spray trials are given.The place of control of Busseola in agricultural practice is described, and some of the present results are quoted to show that yields can be increased by good farming practice as much as by control of Busseola.

SummaryThe Lepidopterous stalk borers that occur in Uganda in association with the Gramineae were studied there during 1954–1956 by collecting on all likely host-plants at two centres and by a country-wide survey in which stalk-borer damage in cereal crops was qualitatively assessed at five-mile intervals along the routes followed, and the species of borer present in such crops and, where possible, in nearby wild host-plants were determined. The commonest Noctuids were Busseola fusca (Fuller), B. segeta Bowden, Sesamia calamistis Hmps. and S. poephaga Tanas & Bowden. All these attacked sorghum, maize, sugar-cane and (except the last) finger millet (Eleusine coracana.); so also did S. botanephaga Tarns & Bowden, but only near swamps, in which it infested sedges (Cyperus spp.) and reeds (Typha australis), from which the other species were virtually absent. Only S. calamistis and S. botanephaga attacked rice. All attacked Pennisetum purpureum, Sorghum vertictlliflorum, Vossia cuspidata, and (except S. botanephaga) Panicum maximum, and also other wild grasses.B. fusca is widely distributed but most abundant in areas of intensive cultivation, where crop residues abound in which the resting larvae can survive the dry season. B. segeta is the most frequent species in Pennisetum purpureum and Panicum maximum, which are extremely common over most of the country, but is rare in cereal crops. S. calamistis (to which earlier records of S. cretica (Led.) and S. vuteria (Stoll) must be attributed) is not numerous but occurs in every district except Karamoja, where it cannot survive the dry season; and S. poephaga is known only from northern and eastern districts and is unimportant.Chilo zonellus (Swinh.), which may be a recent introduction, occurs in all the cultivated host-plants and most of the wild ones except Cyperus and Typha; it has not been found at altitudes above 4,000 ft. in the west or 5,000 ft. in the north and east, but elsewhere it is the prevalent borer and can cause severe damage in dry years and on out-of-season crops. It was the only species besides B. fusca found on bulrush millet (Pennisetum typhoides), the tough stem of which resists attack. On the western border, Eldana saccharina Wlk. attacks sorghum, maize and sugar-cane at high altitudes, and Maliarpha separatella Rag. attacks rice. A fourth Pyralid, Pectinigeria sp., occurs on maize.When small plots of host-plants were grown in a matrix of sorghum, and also in a swamp, and the whole sampled at harvest for borer infestation, all the cultivated hosts and many of the wild ones suffered some attack, the percentage of stems bored varying from 10 (finger millet) to 89 (sorghum) amongst the former, and reaching 34 (Panicum maximum), 40 (Sorghum verticilliflorum) and 50 (Pennisetum purpureum) amongst the latter. Immature stages of C. zonellus and B. fusca greatly outnumbered those of Sesamia, especially in the more heavily infested host-plants.Notes are given on the life-histories of the commoner species of borer and on their habits in the field. In the laboratory, the lengths of the life-cycles, in days, were 68–75 (B. fusca), 65–78 (B. segeta), 46–58 (S. calamistis) and 46–53 (C. zonellus). In the dry season, the larvae of B. fusca entered a resting stage, which prolonged the life-cycle to 200 days; such larvae were found only in living or dry stems of crop plants. C. zonellus and Sesamia spp. bred continuously, in the dry season the former being found chiefly in trash, stubble and volunteer tillers of sorghum, the latter in these and living stems of grasses.Of the principal cereal crops in Uganda, sorghum is the most widespread. The main crop, sown after the longer of the two dry seasons, suffers little borer attack; second crops are more severely affected, but plants with thick stems or numerous tillers nevertheless yield heavily. Finger millet is the staple food crop in the north and west; borer damage is negligible and restricted to small patches of “dead-hearts” caused by larvae from single egg-masses of S. calamistis. Maize is grown on a large scale in the districts bordering Lake Victoria and in the highlands; borer attack is usually very late and, where rainfall is adequate, appears not to afiect yields.Apanteles sesamiae Cam. and another, unidentified, Braconid probably control S. calamistis, but on the other stalk borers the incidence of parasites, which are listed, is low. Destruction of all crop residues and wild species of Sorghum around cultivated areas would considerably reduce borer attack at the beginning of the growing season, but chemical control was only partly effective and did not increase the yield.

Busseola fusca (Fuller) is a serious pest of maize and sorghum in Tanganyika where it occurs mainly at altitudes of 4,000 ft. and over.Laboratory work on the life-cycle and on the diapause of the larva is described. Diapause is terminated by contact with water.Field work at Nzega, Western Province, indicates that the first sowings, made within two to three weeks of the beginning of the rains, are likely to be heavily attacked by larvae of the first generation. These are the progeny of a “raininduced” flight of adults of Busseola derived from diapause larvae in the maize and sorghum left in the fields from the previous season, the larvae being induced to pupate when the stems are wetted by rain.The number of generations in the main crop season, November–June/July, is two. A third generation occurs in sorghum tillers produced after June/July.No alternate hosts of importance comparable with maize and sorghum have been found.Cultural control by burning the crop residues left in the field after harvest, in order to destroy the diapause larvae, is not practicable in peasant agriculture as these residues are required for such purposes as palisading, building of contour banks and for grazing cattle and goats during the dry season.Chemical control of the first generation of Busseola in young maize can be achieved by the application of a dust containing 2·5 per cent. DDT into the funnel of the plant. In 13 experiments on peasant-owned plots at Mbeya, in which a dust containing 2·5 per cent. DDT was applied four times, at weekly intervals, beginning about 18 days after germination, and at the rate of 10 lb. per acre, the average weight of maize cobs from 100 plants was increased from 12·46 to 22·82 kg., an increase of 83·1±19·0 per cent. Factors other than Busseola which affect the yield are discussed and it is suggested that control measures would probably be worthwhile only where a combination of a suitably fertile soil, early planting and adequately distributed rainfall obtains.

Five trials were conducted in Kenya in 1962–63 to investigate the effectiveness of a 0·2 per cent, w/w pyrethrum dust, synergised with 5 parts piperonyl butoxide to 1 part pyrethrins, against the stalk borer Busseola fusca (Fuller) by applying it to maize at 20 lb. per acre. In three trials, it was compared with a dust containing 5 per cent. DDT applied at the same rate. Pyrethrum showed an efficiency in controlling B. fusca equal to that of DDT. Both insecticides produced reductions of more than 50 per cent, in the incidence of infestation, and in the final trial there was a significant reduction of over 40 per cent, in the number of cobs damaged by stalk-borer larvae; at the same time, an increase in yield was apparent. Further work is required in order to determine the lowest effective concentration of pyrethrins in the dust, which is likely to be less than 0·2 per cent., and to indicate the best time of application.