In view of the losses of harvested grain incurred due to problems related to storage, marketing, transport, and handling, this paper reviews the situation on storage of food grains in developing countries. It lists the insect pests that frequently attack stored food grains in these countries and discusses strategies that would minimise the damage caused by the pests.

Field studies were conducted to characterise the effects of infestations by adult and nymphal stages of cowpea aphid, Aphis craccivora Koch, on the growth and yield of cowpea, Vigna unguiculata (L.) Walp. Seedling, flowering, and podding stage plants of aphid-resistant (cv. ICV-12) and aphid-susceptible (cv. ICV-1) cowpea cultivars were used in the studies. Four treatments (consisting of infestations with adult and nymphal aphids, caged controls and uncaged controls) were administered on plants for 22 days post-treatment. Eight parameters of crop success were measured: extended leaf heights (ELH); plant mortality; incidence of sooty mould; incidence and abundance of natural enemy species; crop growth parameters (net assimilation rate, [NAR] in g/ dm2/day, and crop growth rate [CGR] in g/dm2 land surface/day); and plant yields (seeds per pod, weight per seed). Data were analysed using analysis of variance (ANOVA), orthogonal contrasts and 95% confidence intervals (C.I.). There were no significant (P > 0.05) differences between adult and nymphal infestations or between caged and uncaged controls, so the respective sets of data were combined for comparisons of aphid infestations with control treatments. Infestations caused severe plant stunting and other growth deformities, drastic yield reductions, higher plant mortality, greater incidence of natural enemies and abundance of Cheilomenes spp. on cv. ICV-1 than on cv. ICV-12, and on infested and uninfested plants. Aphid infestations did not significantly affect the incidence of sooty mould on plants of cv. ICV-12 or cv. ICV-1.

Seven-day-old seedlings of 22 rice cultivars with dominant Glh1, Glh2, Glh3, Glh5, Glh6 and Glh7 and recessive glh4 genes were evaluated for resistance to the green leafhopper (GLH), Nephotettix virescens (Distant), in a no-choice seedling test under uniform infestation at four nymphs per seedling. “IR29” (gene not identified) was the resistant check, while “Taichung Native 1” (no resistance gene) was the susceptible check. Maximum reproducibility for resistance score was obtained 11 days after infestation. “Pankhari 203” (Glh1), “Kalimekri 77–5” (IRRI Accessions 6613 and 6622) (Glh1), “ASD7” (Glh2), “DNJ97” and “Arai” (Glh3), “ASD8” (Glh5), “PTB18” (Glh6), and “Laki 65” (IRRI Accession 6622) and “Lasane” (Glh7) showed consistently resistant reaction under the no-choice test. The lines could be used for allelic studies of GLH resistance and for gene pyramiding.

Margosan-O®, a commercial neem-based insecticide, incorporated into an artificial diet prolonged the development of larvae of Spodoptera littoralis Boisduval. It also affected the rate of adult emergence at the end of pupation. Larvae treated during one stadium continued to show the effects of their previous exposure. The susceptibility to Margosan-O was more pronounced when larvae ate the diets containing Margosan-O for the first time during the fifth or sixth instar. The results indicate that Margosan-O has an activity similar to that of other neem-seed extracts. In the course of this work morphological anomalies were also recorded. The most striking was the appearance of black stripes on the abdominal tergites of the fifth and sixth instar larvae fed on diets containing 0.01, 0.05 or 0.1% of Margosan-O.

A technique for infecting adult tsetse with an entomopathogenic fungus was developed and tested in the laboratory. A nitrocellulose filter membrane (Millipore) was used as substrate for retaining conidia after fitration, and a cylindrical plastic tube served as a chamber for the flies. The technique was designed to allow accurate estimation of inoculum on the substrate, thereby permitting comparison of virulence during the screening of fungal pathogens against tsetse flies. Glossina morsitans centralis adults were susceptible to Metarhizium anisopliae at all doses tested, and mortalities were dose dependent. No significant differences in mortalities were observed when flies were exposed for different durations to the pathogen. The number of conidia picked up by flies varied considerably with exposure time and concentration.

The spore replication rate of the parasitic microsporidian, Nosema bombycis, was investigated in the pupal and adult stages of two popular tropical silkworm races of India, Pure Mysore (multivoltine race) and NB18 (bivoltine race). The rate was assessed in terms of spore yield per unit weight of tissue. In pupae, spore replication in the bivoltine race was higher than that in the multivoltine race. Spore replication in both races followed a logistic pattern. Spore production increased substantially with age of moths in both races. The cephalothoracic region of each race had the highest spore concentration, especially around the wing and wing muscles.

Eleven mosquitocidal Bacillus thuringiensis isolates from Nigerian soils were screened for the degree of toxicity against Aedes aegypti larvae. The six most larvicidal isolates, code-named OBGI, OBG8, BUS4, BAR3, GSC3 and GNA13, were identified as subsp. israelensis (B.t.i). Spores of the six isolates of a B. t. i. from a commercial powder (R-153–78, Roger Bellon Laboratory, Belgium) and of IPS 82 (Institut Pasteur (Standards)) were subjected to ultraviolet irradiation (280–350 nm) for up to 75 min. After irradiation, the toxicity of OBG8, OBGI, BUS4, and BAR3 was higher than that of R-153–78 but lower than that of IPS 82.

The ovisite preference of Goniozus nephantidis (Hymenoptera: Bethylidae) was studied in relation to its hosts, Opisina arenosella, the coconut pest and Corcyra cephalonica, the flour pest. In both hosts, eggs were laid on all the segments except the first thoracic and the last four abdominal segments. Among the abdominal segments, the most preferred were segments 2 and 3 in the case of O. arenosella and 4 and 5 in the case of C. cephalonica. The percentages of eggs located intrasegmentally were 91.35 and 86.19; those of eggs located intersegmentally were 8.65 and 13.80 in the case of O. arenosella and C. cephalonica respectively. The left side was preferred in each host. In most of the egg clutches on O. arenosella, the head end faced the caudal end of the host; on Corcyra cephalonica, the head end faced the head end of the host.

Several mounds in western Kenya were excavated to examine their internal structure. The mounds and the soil beneath them were found to be densely packed with discrete chambers containing fungus combs. A simple system of passages opening to the exterior provided both access and ventilation to the interior of the nest. One nest was killed by fumigation and its contents extracted. The nest population was estimated to be 0.28 million adult steriles with a biomass of 462 g dry weight, and the total dry weight of fungus comb was 2.8 kg. These estimates are very low in comparison to nests of Macrotermes spp. that build mounds of comparable size. The ratio of fungus comb weight to adult biomass (6:1) is higher than that in Macrotermes spp., perhaps because the comb is constructed in a different way.

Studies were carried out on the neonatal development of Riptortus dentipes (Fabricius) and Nezara viridula (Linnaeus) on pods of cowpea Vigna unguiculata (L.) Walp (var. VITA-3) and soybean Glycine max (L.) Merrill (TG× 536–02D). Both crops sustained nymphal development and adult reproduction of R. dentipes. Nymphal duration was 20.7 days on cowpea and 21.3 days on soybean; mean adult weight was 56.3 mg (male) and 58.3 mg (female) on cowpea and 55.8 mg (male) and 57.6 mg (female) on soybean. Adults preferred soybean to cowpea for egg laying though a substantially higher number of eggs was laid on the mesh walls of the cages indicating the somewhat suboptimal nature of both plant substrates. The nymphal period for TV. viridula was 24.4 days on cowpea and 25.4 days on soybean, and the mean adult weight for males was 139.0 mg while that for females 186.0 mg on cowpea. On soybean, the mean adult weight was 127.3 mg for males and 176.9 mg for females. Soybean leaves were preferred for oviposition. The concept of host plant suitability to the various stages of these insects with respect to host switches between cowpea and soybean.

A series of life tables (22 generations) for the rice yellow stem borer, Scirpophaga incertulas (Walker), a major pest of rice in Bangladesh, was constructed. In a deepwater rice ecosystem, the S. incertulas population dropped to a low level in the second or third generation (May-June), then reached the annual peak level in the fifth generation during September-October. The population dropped again to the lowest level in the sixth generation (November-February) when the larvae remained in diapause for about 3 months. In general, the population suffered very high mortality (99%). The estimated egg mortality was 49%; about 96% of the hatched larvae failed to penetrate into the rice stem; 39% larvae and 27% pupae died inside the stem. The population suffered very high mortality (96 %) at the early larval stage and the resultant survivorship curve was type III. Key factor analysis revealed that the disappearance of newly hatched larvae before penetration into the rice stem was the key mortality factor responsible for population fluctuations between generations. Disappearance of young larvae and egg mortality were density-dependent, but of a weak type.

Studies were conducted in several ecological regions of Côte d'lvoire from 1986 to 1990 to monitor maize cob-borer populations and to investigate losses in maize grain yield due to this pest. The relationship between borer abundance and crop losses was studied using regression analyses, in which two regression models were developed. One model related yield loss to number of damaged grains and the other related yield loss to grain weight. Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) was the dominant pest in most localities. Its population density was particularly high in the semi-deciduous rain forest and decreased westwards and northwards. The models explained 85.6% (yield loss vs damaged grains) and 72.5% (yield loss vs loss in grain weight) of the observed variation. Moreover, they showed that the weight loss due to cob-borers was much lower than that due to stem borers and also that the number of damaged grains increased rapidly with borer density.

Populations of adults of Smicronyx guineanus Voss and Smicronyx umbrinus Hustache were sampled on the witchweed Striga hermonthica (Del.) Benth, in Burkina Faso. Samples were taken at four localities in 1991 and at one locality in 1992 and 1993 using a Univac portable suction sampler, beginning at emergence time of the adult weevils, to assess their dispersion patterns and the optimum sample size for Smicronyx. Sampling was done weekly by placing the 60-mm-diameter suction cone on a Striga plant until it was about 5 cm above the ground. Smicronyx adults on S. hermonthica were aggregated. A sample size of 20 and 126 units provided a 25 and 10% precision level respectively at six Smicronyx adults per sampling unit. A chart was designed which could be useful for determining the level of precision attainable at various densities of Smicronyx adults for sampling and monitoring programmes. Larval vertical distribution of Smicronyx was described. Striga plants were stratified with respect to distance from the base and categories were designated as upper, central and lower parts. Results indicated that Smicronyx larvae were located in the upper stratum of the witchweed where they made galls and destroyed large numbers of seeds.

Results of a field survey of certain host-related and off-the-shelf compounds as possible attractants for the black fly, Simulium arcticum (Malloch) (IIS-10.11) (Diptera: Simuliidae), are reported. Silhouette traps were baited with carbon dioxide and candidate attractants in an incomplete randomised block design. Carbon dioxide alone exerted a strong attractant effect on this species. Both acetone and crude whole body odour of cattle (tested in combination with carbon dioxide) were significantly more attractive than carbon dioxide alone (control). Although bovine urine produced larger catches than control (carbon dioxide only) traps, the effect was not statistically significant. Other odours tested in combination with carbon dioxide, including fractions of the crude bovine odour and l-octen-3-ol (a potent tsetse fly attractant), were without apparent attractant effect when compared to the carbon dioxide-only control.

Several terpenoids and oils were screened for vapour toxicity and repellency against the termite, Odontotermes brunneus. In toxicity tests, knockdown time KT50 and KT90 values were derived at 5 mg/cm2. For repellency screening, a new experimental setup was designed and effective time ET50 and ET90 values were determined at 2 mg/cm2. Among the compounds screened, eucalyptus oil produced the fastest knockdown (KT50 24.8 min) while β-ionone was found to be the least effective (KT50 536.0 min). Terpeneol (anhydrous) afforded maximum persistence of 338.0 min, whereas the least persistence was obtained from linalool (78.9 min) which prevented 50% of the population from crossing over the treated barrier (ET50).

The quantitative and qualitative changes of bacterial flora associated with the silkworm (Bombyx mori) at different stages of its life cycle were studied. Larvae reared on mulberry leaves were dissected and their bacterial populations counted after a 3-day incubation period at 28 ± 2°C. The results showed a higher heterotrophic bacterial population in the fourth and the fifth instars, which coincide with the active feeding stage of the larvae. The similarity of the genera observed in the digestive tract and that observed on the leaves fed to the larvae suggests colonisation of food microflora in the gut following ingestion. The bacteria inhabiting the gut of silkworm were found to be elaborating amylase, caseinase, gelatinase, lipase and urease. The highest percentage of isolates were protease producers followed by lipid and polysaccharide splitters. The results indicate that the bacterial flora play an important role in the digestion of ingested food material.

The effect of methionine on longevity, antioxygenic enzymes and lipid peroxides in Callosobruchus maculatus was investigated using C. maculatus maintained on Vigna radiata seeds soaked in seven levels of methionine, 0, 1, 3, 5, 7, 9 and 12 mg/ml water. The life span and activities of catalase and peroxidase were higher in Callosobruchus maculatus infesting Vigna radiata seeds soaked in methionine as compared to their control cohorts. However, the lipid peroxide (malondialdehyde; MDA) levels generally remained unaltered. The present observation on the increased longevity in C. maculatus with methionine level is an extension of earlier findings on its anti-ageing effect in higher animals.

Insecticides belonging to the four major groups were bioassayed against Helicoverpa armigera Hubner collected from cotton in the Guntur region of Andhra Pradesh, India, during the 1989/90, 1990/91 and 1991/92 cropping seasons. High levels of resistance to all groups of insecticides were recorded. Tolerance to quinalphos had increased drastically in the 1991/92 season, while resistance to endosulfan, monocrotophos and carbaryl had increased moderately. The populations were also highly resistant to cypermethrin and deltamethrin and mildly resistant to fenvalerate. The resistance levels varied from season to season, thus reflecting the selection pressure created through insecticides.

Over 300 male specimens of Atherigona lineata from the Natural History Museum, London, the Regional Museum of Wales, Cardiff, and various parts of Nigeria including the Institute for Agricultural Research Insect Museum, Samaru, were examined using the binocular microscope, to determine the extent of variability in this species. Three hundred and twenty-six male specimens of Atherigona lineata (Adams) segregated into 10 forms based on variability in the shape and chaetotaxy of the trifoliate process, with minor individual variations observed within some of the forms. Variability was observed in the extent of infuscation of the fore femur. Generally, the hypopygial prominence, which is bilobed, also showed some variability in the length and width of the lobes.

The oak tasar silkworm, Antheraea proylei J., was reared on the foliage of Quercus serrata Thunb., Q. griffithii Hook. fil. and Thoms, and Q. dealbata Hook, fil and Thoms. under controlled indoor conditions to assess the suitability of these plants as feed for the silkworm. Relative growth rate of the silkworm was lowest on Q. dealbata, perhaps due to the relatively low level of crude protein and high level of crude fibre in this species. These results show that Q. dealbata is a nutritionally inferior food plant in comparison with Q. serrata and Q. griffithii.