Economic injury level (EIL) by the sorghum earhead bug was estimated for nymphs, feeding adults and ovipositing adults of sorghum earhead bug, Calocoris angustatus Lethierry, using malathion or hexachlorocyclohexane (HCH) as insecticidal control measure. EIL varied according to the insecticide used and the stage of the insect. EIL per panicle was 7.9 nymphs, 5.4 feeding adults or 0.06 ovipositing adults when HCH was used, which increased to 15.1 nymphs, 10.5 feeding adults and 0.12 ovipositing adults when malathion was used for control.

The effect of growing cowpeas mixed with either beans or maize on population densities of Megalurothrips sjostedti (Trybom) was investigated. Also investigated was the effect of varying the cropping densities of the host plants on the pest populations.

There was a significantly lower population of M. sjostedti in cowpea/maize, bean/maize, and cowpea/bean/maize mixed stands as compared with that in either cowpea/bean stands or monoculture stands of cowpeas and beans. Increasing the cropping densities of the host crops increased the abundance of the pest in non-maize based mixed stands, but this effect was not observed in the maize-based mixed stands.

The results indicate that with regard to infestation by M. sjostedti, the practice of mixed cropping beans with cowpeas confers no advantage to either crop with respect to attack by M. sjostedti. On the contrary, combining the two crops attracted infestation levels similar to those attracted by either crop grown in monoculture. But the inclusion of a non-host plant (maize) in the mixture, significantly reduces infestation.

Combining ability analysis for three stem borer resistance parameters, i.e. “dead hearts”, leaf injury and stem tunnelling, revealed that both additive and non-additive types of gene effects were involved in the inheritance of these attributes. The specific combining ability (sca)/general combining ability (gca) variance ratios further indicated predominance of additive gene effects for stem tunnelling and non-additive effects for “dead hearts” and leaf injury. The genotypes, IS 2123 and IS 5469 are good general combiners for all the three parameters. Among F1 hybrids, IS 1054 × IS 5469 and IS 18551 × IS 2123 expressed good sca for all the parameters of stem borer resistance. The use of IS 2123 and IS 5469 parental genotypes in the future breeding programmes is suggested.

Laboratory-reared tsetse, Glossina pallidipes were inoculated with the tsetse virus by microinjection into the haemocoel, and feeding through micropipettes. The inoculated tsetse were reared on rabbits for 45 days, and feeding, flight and mating activities recorded. The tsetse were dissected and the conditions of the salivary glands and gonads noted. In males, tsetse were examined under a compound microscope and the presence of spermatozoa noted. F1 pupae were allowed to emerge, dissected, and the salivary glands examined for hypertrophy, and the gonads for sterility.

There was no reduction in the activity of inoculated tsetse. Infection level was 23.5% in the treated adults. All infected ♂♂ were sterile while ♀♀ were fertile. There was no significant difference in the maternal age at larviposition, F1 pupal weight, or incubation period of F1 pupae, between treated and untreated tsetse.

A high proportion of F1 adults (65%) were infected, with category four hypertrophied salivary glands. All males with enlarged glands were sterile. The evidence obtained shows that the tsetse virus may be used in biological control of G. pallidipes.

Studies on seasonal patterns of okra leafhopper, Amrasca biguttula biguttula Ishida were conducted for two years. Time series analyses were adopted for working out weekly seasonal index of okra leafhopper. Low incidence of leafhopper was recorded from June to mid-January. Results further revealed that incidence of leafhopper was highly correlated with minimum temperature. There was no discernible time lag for population increase of leafhoppers. Prediction of leafhoppers at different crop growth stages for various months of sowing was done using dummy variable technique.

An investigation was carried out in India, to study the extent of heterosis expressed in single, three-way and double cross hybrids with respect to important economic characters. The results were discussed in terms of relative heterosis (heterosis over mid-parent value) and standard heterosis (heterosis over standard check variety). Significant negative relative heterosis was observed for total larval duration in single and majority of the three-way crosses; whereas it was positive and significant in double cross hybrids. The commercial characters like cocoon and pupal weight, shell percentage, filament length and denier, recorded positive relative heterosis in most of the single and three-way crosses; whereas they were negative and significant in most of the double crosses. In general, higher degree of heterosis was expressed in single crosses followed by three-way and double crosses for the characters studied.

The number of instars in the silkworm Anaphe venata was determined using three methods namely: (1) direct observation of cast exuviae by larvae reared through the entire larval stage, (2) use of frequency distributions of head capsule lengths and widths taken from larvae representative of the entire larval stage of the species and (3) morphological observations and examinations of larval segments and anal plates. Seven instars were observed for A. venata. The most reliable method was the direct observation of cast exuviae by larvae reared through the entire larval stage. It is further suggested that either the method of histograms of head capsules or examination of larval segments and anal plates be used to supplement this method for better reliability.

Females of Bruchidius atrolineatus (Pic) lay their eggs in the fields on maturing or dry pods of their host plant, Vigna unguiculata. Under experimental conditions in the presence of maturing and dry pods connected with the plant, 80% of eggs are laid on maturing pods. The preference for maturing pods is observed in two generations of B. atrolineatus and varies with the age of females. In the presence of pods separated from the plant, 69% of eggs are laid on dry pods. These results show the importance of methodology during insect behavioural studies. In the absence of choice, reproduction of B. atrolineatus females is more stimulated with dry pods than with maturing ones. These experiments show that factors which influence the choice of the pods are probably different from those stimulating oviposition.

Electrophoretic studies were carried out on isozymes of Glossina pallidipes to determine whether there are any genetic differences between natural populations from an area free of sleeping sickness (Nguruman) and an area where sleeping sickness is endemic (Lambwe Valley) in Kenya. Out of 12 enzymes examined, two enzymes, GPI and PGM, showed high polymorphism in the two populations, while the other 10 enzymes were all monomorphic. At the GPI locus, at least five alleles were detected, and two alleles were found at the PGM locus. There was a difference in the frequency of isozyme patterns between males and females, indicating that the PGM locus is on the sex-linked chromosome (X-chromosome). Nei's genetic distance (D) was 0.00154 between the two populations, which is the value within the range for local populations in different organisms examined so far. Some difference between the two populations was found in the level of average heterozygosity (H) and in allelic composition of the GPI locus, that is, the Lambwe Valley population is more heterogeneous than the Nguruman population.

Studies have shown that the East African mosquito strain, Culex pipiens fatigans, is attracted to a synthetic oviposition attractant pheromone in the laboratory. Chemical analysis has shown that the main volatile component of the apical droplets is (—)-(5R,6R) erythro-6-acetoxy-5-hexadecanolide. In contrast to the lack of response in the Sri Lankan strain of the same mosquito, the East African strain shows remarkable similarity in attraction response to the West African, American and Japanese strains of C. p. fatigans.

The intensity of damage to sorghum panicle caused by the sorghum earhead bug, Calocoris angustatus Lethierry (Heteroptera: Miridae) was studied under laboratory and field conditions. Laboratory studies showed that among the five nymphal instars, fourth instars consumed maximum food (5.06mg/day). In adults, the consumption was thrice that of the fourth instar nymphs. Male and female consumed on average 250.68 and 305.56 mg of food respectively from their second instar nymphal stage till their death. In the field, 1–3 days old panicles were preferred for oviposition when compared with panicles at later stages. Grain weight losses upto 31.54 g/panicle infested with three adults were recorded. Similarly the grain weight per panicle decreased as the number of ovipositing females increased; grain weight losses of 9.72–42.02 g were recorded.

In the laboratory, adults of Prostephanus truncatus (Horn) preferred artificially or naturally (insect) damaged maize kernels to sound kernels when adults were tested individually or in groups. Survival of P. truncatus was similar when 1, 10, 40 or 80 adults were fed 100 g of shelled maize for 20 days; but more kernels were damaged at the highest adult density in comparison to the other densities of adults. Single P. truncatus adults on average damaged 9 maize kernels, but 10, 40, and 80 adults damaged approximately 15, 21 and 45 kernels, respectively, indicating that adults confined their feeding to only specific kernels. Survival of adults and number of kernels damaged were significantly affected when different quantities of shelled maize (25–500 g) were infested with 25 adults of P. truncatus. Adult surv at 25, 50, 100, and 200 g of maize/0.95–1 jar was similar (70.7–76.0%), but the number of kernels dama increased significantly from approximately 15 at 25 g to 61 at 200 g. These results suggested that shelled maize grain compaction, which is influenced by the quantity of grain, may affect survival of and damage by adults of P. truncatus. Adults of P. truncatus successfully infested 25 g of shelled maize and damaged about 15 kernels, indicating that adults could temporarily survive on such small quantities of grain spilled in and around storages before infesting stored-maize.

Both sublethal and lethal doses of fenitrothion treatment caused positive temperature toxicity relationship in three lepidopteran fifth instar larvae, Achaea Janata, Mythimna separata and Bombyx mori.

The LD50 value was very low at 30°C compared to 28 and 18°C. In all the three species, the insecticide caused greater rate of regurgitation of body fluid at higher temperature. It is believed that the loss of body fluid causes desiccation and enhances the poisoning effects of fenitrothion.

Seven phenolic compounds (phenol, 3- and 4-cresols, 3- and 4-ethylphenols, and 3- and 4-n-propylphenols) previously shown to be components of a fraction of an extract of buffalo urine which was active as a tsetse attractant, were evaluated in field experiments, individually at different concentrations, and in blends. The results indicate that 4-cresol and 3-n-propylphenol are the most important components for the of the attractancy phenolic mixture.