A survey carried out over Western Kenya in order to determine the prevalence of microorganisms in cereal stem borers and legume pod borer showed the presence of a large number of insect pathogens in the dead larvae. Larval cadavers were recovered from all sampling sites. Bacterial and fungal microorganisms were highly prevalent. Other major groups of microorganisms were also recovered, although at a low level. Viruses (polyhedral inclusion bodies and granulosis viruses) occurred at 2.7% at the Mbita Point Field Station, and 1.1% in the field. Mermithids and rhabditids occurred at 0.4% in the station and 0.6% in the field, whereas the protozoans (microsporidia and gregarines) were more prevalent in the station than in the farmers' fields (9.4 and 1%, respectively).

The spotted stalk borer, Chilo partellus was the most common borer sampled, but Busseola fusca and legume pod borer, Maruca testulalis were sampled in most sites too. Sesamia calamistis and EIdana saccharina were recorded at a low level, and C. orichalcoceliellus was recorded only at the Kenya coast.

In experiments to find the yield loss in soyabean due to the leaf miner, Aproaerema modicella (Deventer) and estimate the economic injury level (EIL), plants were infested at 30 and 45 days after sowing (DAS) with a fixed number of laboratory reared second instar larvae.

Grain yield was not reduced by one larva per plant at both 30 and 45 DAS, but the yield reduction which ranged from 2.7 to 6.1% was significant with two larvae per plant at both the ages. With an increase in larval population, there was a corresponding decrease in yield to the extent of 40% and 66% with 10 larvae/plant at 30 and 45 DAS respectively.

The regression of yield of leaf miner infestation indicated that yield was reduced by 0.463 and 0.716 g per plant for every larva per plant at 30 and 45 DAS respectively. Yield loss was greater in plants infested at 45 DAS than at 30 DAS with all populations tested.

The estimated economic injury level for A. modicella is 0.6 larva/plant at 30 DAS, and 0.2 larva/plant at 45 DAS. The suggested economic threshold level in soyabean of 85–90 days duration is 0.5 larva/plant (1 larva/2 plants) at 30 DAS and 0.2 larva/plant (1 larva/5 plants) at 45 DAS.

Adults of the Caribbean fruit fly, Anastrepha suspensa (Loew) were fed on three diets in order to identify one that was optimal for adult longevity, fecundity and egg viability. The diets were a dry mixture of Brewer's (hydrolysed) yeast and sugar (Diet A); Brewer's yeast, sugar, agar, and water (Diet B); and a dry commercial diet (BioServ) with Brewer's yeast, sugar and casein (Diet C). There were no significant differences in per cent adult mortality among the three diets. However, the longevity of females in Diet C was significantly reduced in comparison to that of females fed the other two diets. Diet C was also suboptimal for fecundity and egg viability. Diets A and B were optimal for and had similar effects on all parameters evaluated in this study. However, Diet A appeared to be the best if preparation time and ingredient costs are considered along with biological effects.

Establishment and maintenance of a laboratory colony of Phlebotomus argentines are described which presently is in the nineteenth generation. Larvae were reared in modified plastic vials and were fed with a newly prepared food. Emerged flies were kept in adult holding cages at 50–90% r.h. and 25–26°C and provided with 30% sucrose solution. The average development time (egg to adult) of each generation in the laboratory was about 32 days at 28–31°C. Adult females were fed blood on hamsters, humans and white mice. Observations were made on mating behaviour, host preference, oviposition, effect of temperature, etc.

Eight potato cultivars namely Anett, Desiree, Feldeslohn, Kerr's Pink, Kenya Baraka, Roslin Eburu, Roslin Gucha and Roslin Tana were tested in the greenhouse to compare their susceptibility to Myzus persicae Sulzer. Differences in the susceptibility of the potato cultivars to aphids were reflected in the number of the apterae aphids that developed on them. Anett, Kerr's Pink and Feldeslohn supported the highest, and Roslin Tana the lowest population of M. persicae. Roslin Tana was found to be resistant. The bottom leaves of most potato cultivars maintained the highest aphid population while the upper leaves maintained the lowest. There were no significant correlations between leaf area and yield of potatoes with the number of apterae aphids on the eight potato cultivars.

Qualitative assessment of nine promising mulberry varieties with two check cultivars was evaluated with silkworm, Bombyx mori (L.). The feeding experiment revealed that ACC-143 and ACC-203 (S-135) varieties were superior to other varieties and check cultivars in all the economic characters of cocoon. The variety x season interaction was highly significant. ACC-143 and ACC-203 showed significantly better results over other varieties.

Culex quinquefasciatus (Wiedemann) mosquitoes, which are refractory to Brugia pahangi (Buckley and Edeson) microfilariae, were fed simultaneously on Wuchereria bancrofti (Cobbold) and B. pahangi microfilariae. A selected stock of Aedes aegypti (L) which is susceptible to both of these filariae was used as a control. The exsheathment and migration rates of B. pahangi in C. quinquefasciatus increased significantly as compared to those of B. pahangi when given as a feed by itself. These two processes did not show any trend with time. On dissection, 12 and 14 days postinfection, 27% of C. quinquefasciatus were found to be infected with an average of two larvae per mosquito. Of the total number of larvae found 78% were W. bancrofti while 22% were B. pahangi.

Feeding C. quinquefasciatus on in vitro exsheathed B. pahangi microfilariae suspended in serum did not increase the rate of migration, whereas 71–100% of Ae. aegypti became infected with a mean of 3.5 larvae per mosquito.

Inoculation of C. quinquefasciatus mosquitoes into the thorax and abdomen with exsheathed B. pahangi did not increase their infection rate, whereas in Ae. aegypti 67–82% became infected.

EAG recordings revealed that from the six substances isolated so far from pheromone glands of Marnestra brassicae females, only (Z)-11-hexadecenyl acetate (Z11-16Ac), (Z)-9-hexadecenyl acetate (Z9-16Ac) and (Z)-11-heptadecenyl acetate (Z11-17Ac) are perceived by the males. This suggests that these substances may be female sex pheromone components.

The male olfactory sensilla also respond to (Z)-9-tetradecenyl acetate (Z9-14Ac) and (Z)-11-hexadecenol (Z11-160H), which are sex attractant constituents of various closely related species, but act as strong attractant inhibitors on M. brassicae males. This sensitivity to Z9-14Ac and Z11-160H is suggested to enhance the males' possibility to discriminate between conspecific and non-conspecific females.

Single sensillum recordings revealed that in 90% of the male antennal sensilla trichodea tested, three cell types (Types A, B, and C) were active. In the remaining 10% only B and C action potentials were seen. The Type C cells are exclusively responsive to the major pheromone component Z11-16Ac. The Type C cells are activated by the attractant inhibitors Z9-14Ac and Z11-160H, and to a small extent by Z11-16Ac. Responses to mixtures of these substances revealed that addition of Z9-14Ac and Z11-160H to Z11-16Ac changed the activity of the A cells only and did not affect the activities of the A and C cells. It is concluded that volatiles which exclusively or predominantly activate the Type B cells induce avoidance behaviour in the males, whereas substances activating the Type C cells evoke sexual behaviour and are attractive. This offers possibilities for relatively rapid electrophysiological determination of substances inducing sexual or avoidance behaviour. The function of the A cells is not yet clear. These cells respond to low concentrations of Z11-16Ac and Z11-160H, which may enhance the males' capacity to distinguish conspecific from non-conspecific females at a distance, when concentrations are low and the C and B cell activities are small.

It is suggested that cells sensitive to Z9-16Ac and Z11-17Ac are present in a limited number of sensilla only.

Various components of the neem tree, Azadirachta indica A. Juss were tested for their insecticidal effects on Sitophilus zeamais Motsen in stored maize. Seed kernel, leaf, flower and bark from the tree in powdered and extract (80% ethanol) form were used at the rate of 2.5g and 2ml respectively per 50g of grain, infested with 20 insects. Pirimiphos methyl and ethanol applied at 25mg and 2ml served as comparative treatment, and control neem products were efficient where used as a preventive measure. The degree of infestation was 3.2 as compared with 53 recorded in curative assay. Ethanolic extracts showed higher toxicity to S. zeamais than the powdered form. Insects after being confined 72 hr to treated grains had a mortality ranging between 29 and 96.4% (powder) and 32.5 to 100% (extract). The index of susceptibility varied from 0.45 (kernel) to 3.87 (bark) in powdered and 0 (kernel or leaf) to 1.76 (bark) for extracts. When leaf or kernel powder was used to protect grain over a 60 day storage period in aerated and non-aerated environment, insect mortality was 100% (kernel), whereas the leaf powder did not show complete insect control in aerated environment (88.1 %). A very high rate of population increase of S. zeamais was observed in the control.

Some aspects of the reproductive behaviour of the tossa jute defoliator, Acraea terpsicore (L.), were studied. The insect mated only once. A horny material was deposited on the female's genital aperture after mating. Mating began on the day of emergence and lasted for 7 days on 10% sucrose solution. Maximum number of matings was on the third day after emergence. Within the day, over 95% of matings was between 0600 and 1800 hr with a peak between 1200 and 1800 hr. Eggs were also laid mainly between 0600 and 1800 hr during the day with a peak between 1500 and 1800 hr. Oviposition which started on the day of emergence lasted for 7 days on 10% sucrose with a peak on the second day. The presence of the male, after mating had occurred, did not significantly affect the number of eggs laid. Adults emerged between 0600 and 1800 hr but mostly before mid-day. Peak emergence for males occurred earlier than that for females. Behavioural activities in courtship, mating, oviposition, and adult emergence, are described.

Adults of various phlebotomine sandfly species were obtained from leishmaniases endemic foci in Kenya using several trapping methods. Ten species were successfully reared from egg to adult in the laboratory; and large colonies of Sergentomyia schwetzi, S. bedfordi, S. ingrami, S. antennatus, S. adleri, S. garnhami, Phlebotomus duboscqi and P. martini established. Generally, the development of Phlebotomus spp. from egg to adult took longer (54.7–57.2 days) than Sergentomyia spp. whose developmental time with the exception of S. garnhami, varied between 36.5–42.3 days.

The present article is one of a series of papers in preparation in which an ecological approach to developing a sound biocontrol programme for cereal stem borers is proposed and outlined. The proposed approach involves detailed population estimation and analysis in relation to crop phenology to determine the role of local natural enemies, evaluation of biocontrol potential of promising biocontrol agents, developing mass rearing and release technology and monitoring the impact of the biocontrol programme. In the example used to illustrate the first step in such a programme, life table analysis of data from a 2-year study on Chilo partellus on maize and sorghum under subsistence agriculture in Western Kenya, showed local predators (and unidentified factors) to contribute up to 97.6 % of generation mortality of the borer in the age interval from egg to early instar larva, while parasitoids and pathogens contributed less than 1 % mortality in the various life stages. Hence, a programme involving conservation and augmentation of local predators and introduction of selected exotic parasitoids of this borer seems appropriate. This represents an attempt to apply life table analysis, taking into account plant phenology, in studying interacting populations under subsistence farming conditions.

Varietal differences with respect to yield losses due to whitefly, Bemisia tabaci Genn. attack were observed at the “sooty-mould level” and “economic threshold (ET) level” of infestation. At the peak infestation level leading to sooty-mould development, the losses varied from 21.7 to 31.8% in boll numbers, 10.3 and 23.7% in boll-weight; 25.9 and 48.9% in seed cotton yield; 12.4 and 153% in seed oil and 29.4 and 66.5% in seed germination among the group of promising new cultures viz., LK 861, LPS 141 and L 389 and other group of commonly cultivated varieties viz., JKHY 1, MCU 5 and ADB 10050, respectively. Besides, the fibre qualities like length, strength, fineness and maturity were also found to be adversely affected.

A schedule of insecticide spray combining two insecticides: Decis®(deltamethrin) and Systoate® (dimethoate) with four times of spray: 35, 45, 55 and 65 days after planting (DAP) was investigated in order to search for the most effective treatment against Maruca testulalis (Geyer) population on cowpea (Vigna unguiculata (L.) Walp). The local cowpea cultivar “Kpodjiguegue” was used to study the onset and fluctuation of M. testulalis larvae infestation on cowpea terminal shoots, flowers and pods. The trial was carried out during the 1985 early cropping season at Abomey-Cala vi. The treatments' effect on M. testulalis in the terminal shoots was not significant at the 5% level of probability because of the very low infestation of this part of the plant. In the flowers and pods, Decis® was better than Systoate® which failed in controlling this borer satisfactorily. In the unsprayed plots (i.e. control), the peak of the natural infestation occurred in the flowers towards 50 DAP and 65% of the flowers were injured. In the pods, up to 89% of infestation by M. testulalis larvae were observed 60 DAP. The lowest yield was recorded from the unprotected plots (322 kg/ha) whereas the treatment 0-Decis®Systoate®Decis® provided the highest yield (1367 kg/ha) and the highest returns.