Earias vittella (Fabricius) feeds on some malvaceous plant species, but has never been reported to attack Thespesia populnea Cav., even though this plant belongs to the same family. The factors responsible for the failure of E. vittella to establish on T. populnea were, therefore, studied. When whole fruits or fruit pericarps of this plant were provided as larval food, larvae failed to develop and none of them pupated. However, on developing seeds of these fruits, larval growth and development were normal and comparable to those of larvae reared on developing seeds of the most favoured host plant, Abelmoschus esculentus Moench. Ether extracts from fruit pericarps exhibited antifeedant and antibiosis activity against this insect. Ether as well as ethanol extracts affected oviposition to some extent. In a choice situation, significantly less eggs were laid on treated than on untreated okra fruits. However, in a no-choice situation most of the eggs were laid on treated okra fruits.

The major alkanone constituents of the resin of Commiphora rostrata, 2-decanone and 2-undecanone, and a series of structural analogues were bioassayed for their repellency against the maize weevil, Sitophilus zeamais in olfactometric assays. All the aliphatic ketones and aldehydes showed comparable or greater activity than the synthetic commercial insect repellent N, N-diethyl toluamide (DEET). In the 2-alkanone series the C-8 and C-9 compounds demonstrated significantly higher activity than their shorter- and longer-chained congeners. Analogues differing in the relative positions of the carbonyl group, including aldehydes, showed a variable pattern of repellency. Alkanols appeared to be mildly attractive to the weevil. The results support our previous suggestion that the resin constituents may play an allomonal role in the ecosystem where the plant thrives.

A quantitative index of resistance to ticks, which had been derived from results of artificial infestation of East African zebu cattle with a Rusinga Island (Lake Victoria) stock of Rhipicephalus appendiculatus, was tested for consistency using three additional tick stocks—from a laboratory (Muguga), Intona (Trans Mara) and Ukunda (Kenya coast). Results from all the stocks gave similar indices when compared with corresponding values for the Rusinga stock, confirming both the validity of the mathematical function and of the use of any local stock of the tick species for assessing the resistance of cattle to R. appendiculatus.

Several strains of Hyphomycetes fungi were assayed in the laboratory to determine their pathogenicity against second instar Chilo partellus Swinhoe larvae and fifth–sixth instar Busseola fusca Fuller larvae. Pathogenic activity to both stem borers was demonstrated with Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin. B. bassiana isolates caused mortality of 3–100% of mortality in C. partellus larvae, and 30–84% in B.fusca. Strains of M.anisopliae showed a high level of virulence for both insect pests, causing mortality levels of 65–100%. Development of fungal infection appeared to take longer in B. fusca larvae (LT50 of 6.2–13.2 days) than in C. partellus (LT50 of 1.9–5.4 days). B. bassiana isolate ICIPE 4, and M. anisopliae isolates ICIPE 18 and 30, which were effective against both stem borers, outperformed the other pathogens tested. They appear to have potential for use asmicrobial agents in the control of C. partellus and B. fusca.

The effects of six constant temperatures ranging from 15 to 40°C on the rate of development, progeny production, sex ratio and adult longevity of the grape mealybug parasitoid, Anagyrus dactylopii (How.) were determined. It was found to complete the development in the temperature regimes of20–35°C but neither sex emerged as adults at 15 and 40°C. Developmental time of male and female decreased from 32.75 to 10 days, and from 34.50 to 11.75 days respectively, as the temperature increased from 20–35°C. Progeny production increased with the rise in temperature up to 30°C, and a maximum of 182 offspring emerged at 30°C. Sex ratio was altered considerably by different temperatures. Maximum female progeny was also obtained at 30°. Adult longevity of both sexes declined with increasing temperature. Mean longevity of male reduced from 2730 days at 15°C to 2.75 days at 40°C. The findings on the effects of temperature in relation to the rearing in the laboratory and the activity of Anagyrus dactylopii in the field are also discussed.

Six amide alkaloids of Piper guineense were tested for antifeedant activity against fifth instar larvae of Chilo partellus in choice assays. These amides include piperine, Δα, β-dihydropiperine, wisanine, Δα, β-dihydrowisanine, trichostachine and N-isobutyl-trans-2-trans-4-eicosadienamide. Piperine and its dihydrosaturated derivative exhibited the most potentantifeedant activity. Δα, β-dihydrowisanine and trichostachine were intermediate in activity followed by wisanine. The N-isobutyl derivative was the least active. These results suggest that the presence of a methylenedioxybenzene and an alicyclic amide group in the compound may be crucial for high antifeedant activity.

Surveys were conducted in 1981, 1983 and 1984 across the island of Puerto Rico to determine the effects of patch characteristics of the tropical herbaceous legume, Crotalaria pallida Ait. on the herbivore and its parasitoids. The mean number of flower racemes per plant and mature pods per raceme varied from year to year and appeared to be influenced by rainfall patterns, but were independent of patch size or plant density. Low larval parasitism was also observed during dry seasons. Proportion of plant patches colonized by Etiella zinckenella was smallest during dry seasons. Local extinction of C. pallida patches was found commonly, with a 77.4% extinction rate during a 6-month period. Patch extinction, which was caused mainly by human activity, was independent of patch size.

Pods of C. pallida within patches were inspected for lima bean pod borer, E. zinckenella (Lepidoptera: Phycitidae) injury. The number of pods bored per mature raceme, and the per cent of bored pods were positively correlated with the number of host-plants per patch and the (surface) area of the patch. No correlation was found between per cent parasitism and pod borer larval density. However, per cent parasitism was influenced directly by C. pallida plant density and patch surface area. Given the transient nature of C. pallida patches and the changes that occur over a season, these positive responses of parasitoids to plant density and patch surface area are important components for their successful exploitation of larval hosts.

Competition between Plodia interpunctella (Hubn.) and Ephestia cautella (Wlk.) was studied in groundnuts and in a limited amount of standard medium (maize meal, wheat bran and glycerol at the ratio of 8:8:1) (w/w) when the species were reared separately (conditions PI and EC), when one was added before the other (conditions P+E/2 and E+P/2) and when both were introduced together (condition PI/EC). Separately, each species was well maintained on the standard medium, while E. cautella was the better competitor in groundnuts under conditions E+P/2 and PI/EC. The results offer a possible explanation for the pest status and distribution of the two moths species in groundnuts and where their ranges overlap, especially in the tropics.

An experiment was undertaken at two locations in Nigeria to identify the major insect pests of cowpea, assess the yield losses caused by them and recommend profitable control packages. Various combinations of insecticidal applications were tested at four crop growth stages, in conjunction with varieties possessing moderate levels of resistance to one or two insect pests. Flower thrips were the most important pests, followed by pod sucking bugs and foliage pests. The resistance levels of the varieties did not contribute much to reducing yield losses. Yield losses of upto 75% were caused by insects attacking cowpea during the flower bud and flowering stages, and of 23% by insects attacking during pod development. Insects attacking during the foliage growth stage had little effect on yields. Profitable spray schedules which increased yields by about 50–200% were: three sprays at flower budding, flowering and podding (the optimum), the sprays at either flower budding and flowering or flower budding and podding depending on the location, and one spray at either flower budding or flowering stage. Other spray combinations were also viable, but less profitable. Appropriate recommendations for various categories of farmers are given.

The ability of a Kenyan sandfly species, Sergentomyia ingrami, to feed on various species of native or indigenous and exotic or introduced plants of Kenya was investigated using the Anthrone test. Some flies contained more sugar than others when they were tested after exposure to the plants.

Polyacrylamide gel electrophoresis was carried out on Nephotettix virescens (Distant) adults collected from India, Sri Lanka and the Philippines, and maintained in glass-houses on rice variety TN-1 at the University of Wales, Cardiff, United Kingdom. The following enzymes showed activity and were recorded: acid phosphatase (ACP), a-glycerophosphate dehydrogenase (aGPD), fumarase (FUM), glucose-6-phosphate dehydrogenase (G-6-PDH), glutamate dehydrogenase (GLUD), glutamate oxalo-acetate transaminase (GOT), hexokinase (HK), lactate dehydrogenase (LDH), malic enzyme (ME) and xanthine dehydrogenase (XDH).

The bands in nine enzymes were homologous across the three populations and showed no differences.The relative mobility of the enzyme GLUD in the Philippines population was lower than in the other two populations and could be used for diagnostic separation.

The results confirm previous reports of differences in the relative mobility of esterase bands of the Philippines population of N. virescens from India and Sri Lanka populations on starch gel.

Bioassays against the fourth instar larvae of mosquito, Culex pipiens pipiens showed that the non polar part of the duck weed, Lemna minor extracts has a high insecticidal action. On the other hand, these extracts contained synomones of the duck weed which repelled the ovipositing females. By using concentrations equivalent to LC25, the survival resulting by the n. hexane was the least. The tolerance for the sublethal doses was associated with malformations in all stages. First instar larvae and recent pupae were more susceptible to the duck weed synomones than the other larval instars. The duck weed synomones repelled the ovipositing females of Piophila casei and have had an insecticidal effect on larvae and reduced resulting adults. When larvae of Spodoptera littoralis were subjected to sublethal doses of duck weed extract, malformations in the subsequent stages were found.