A positive mean correlation was observed between engorged larval weight and unfed nymphal weight. Similarly, positive linear correlations were observed between engorged nymphal weight and unfed adult weight, between unfed female weight and engorged female weight and between engorged female weight and egg batch weight. Positive linear correlations were also observed between scutal length and weight of unfed adult ticks and between the duration of survival and unfed weight of adult ticks at both 43 and 85% r.h. and 28°C. At 43% r.h. and 28°C, small ticks lost water faster than larger ones. At 96% r.h. and 28°C the small ticks also gained water faster than larger ones. For the sizes tested, all the male ticks were comparable in their ability to fertilize normal females, but the smallest females were incapable of reproduction.

Early instars of Zonocerus variegatus fed on most weeds, but preferred those in the families Euphorbiaceae and Solanaceae. Plants that were accepted initially were lesser consumed than later chosen ones. Although there was no apparent difference between weights of nymphs fed on cassava and other plants in the first 9 weeks; thereafter, cassava fed insects excelled others. Somatic growth was not affected by feed type.

The biological effects of six insect growth regulators (IGRs) AI3-37634-c, AI3-36877-b, AI3-37603-b, AI3-36807-b, AI3-37837-a and AI3-36809-a against immature stages and adults of Aedes aegypti have been evaluated. According to IC50 values obtained (concentration to inhibit the emergence of 50% of adults), AI3-36809-a (0.02μg/ml) proved to be the most effective compound, followed by AI3-37603-b (0.04μg/ml), AI3-37837-a (0.11μg/ml), AI3-36807-b (0.17 μg/ml), AI3-37634-C (0.48 μg/ml) and AI3-36877-b (1.4 μg/ml), respectively. The results showed also that the duration of the fourth instar larvae of A. aegypti was prolonged when these larvae were exposed to the effective concentrations of the above compounds.

Apart from delayed lethal action, possible effect of the compounds tested on the basal follicle numbers developed by females of A. aegypti which survived after larval treatment with IC50 of the above-mentioned compounds has been considered. Generally, the results indicate that the females treated have more follicles than the untreated ones of similar age and grown under identical conditions.

The population and distribution pattern of the black parlatoria scale, Parlatorio zizyphus (Lucas) have been investigated. This scale had two annual peaks of abundance in September and May. It passed through three annual generations, the first in September–October, the second in March–April and the third in June–July on grape fruit trees. The build up of insect population on different zones of grape fruit trees in different seasons of the year was studied. The insect distribution of different insect items were significantly affected at different heights and directions of the trees. The highest population tended to be accumulated on the lower and middle shady zones of the trees in different seasons. With regard to directions the central core of the tree harboured the highest population followed by the west direction and the lowest population was accumulated on the north or south direction in the fall and spring. In summer, the highest population settled on the south direction in contrast to the east or north directions, which harboured the lowest population. The mode of insect distribution is discussed in correlation with the environmental conditions.

Ground spraying trials with different dosages of deltamethrin wettable poweder (NRDC 161) were carried out against G. palpalis (s.l.), vector of sleeping sickness, in January and November 1981 in the Bouaflé human trypanosomiasis focus, Ivory Coast. Three dosages have been tested: 60 g of active ingredient (a.i.) per ha at a concentration of 0.08% in January; and 20 and 12 g of active ingredient per ha in November at 0.027 and 0.016%, respectively. Each dosage has been applied once as a residual spray; spraying apparatus used was the atomiser Solo Port 423. The knock-down and short-term effects of the insecticide were very satisfactory: 90–98% reduction in apparent density of the vector was obtained during the first 2 months after treatment with all the three dosages applied. In the long term, 2–4 months after spraying, more than 95% reduction in apparent density of G. palpalis (s.l.) was achieved even with the lowest dosage of 12 g (a.i.)/ha. The highest dosage of 60 g (a.i.)/ha does not seem to increase significantly the persistence of the insecticide nor the mortality rate of the vector in the study area. In order to reduce the cost of a tsetse control programme and also to minimise insecticide impact on non-target organisms, it is therefore recommended that deltamethrin w.p. be applied at the lower dosage of 12 g (a.i.)/ha in residual ground spraying.

Differences in the susceptibility or resistance of different plants to an insect are reflected in the magnitude of its population established on them and the resulting damage. The population of an insect on a plant is determined by an interaction between its responses and the plant's characters. As explained previously, the following six main types of responses, operating in as many stages, are involved in the establishment of an insect on a plant: (1) orientation, determining the insect's arrival on or avoidance of a plant in response to its attractant or repellent stimuli; (2) feeding responses, determining the quantity of food ingested from the plant; (3) metabolic responses involving the utilisation of the ingested food and determining the insect's nutrition; (4) development of the insect, if in the larval stage, determined by the quantitative food-intake and nutrition; (5) egg-production in the adult stage, determined by the quantitative food-intake and nutrition; and (6) oviposition.

The first, second and last of the above mentioned responses are behavioural which determine the initial selection or rejection of a plant by an insect. In order, therefore, to understand the principles governing the susceptibility/resistance of plants to an insect species, it is necessary to compare the above mentioned responses to susceptible and resistant plants and, next, to examine the role of the plant characters in determining these responses.

On the basis of the existing literature on the subject, the role of different behavioural responses of insects to plants and their characters in determining their susceptibility or resistance to their insect pests has been considered in this paper.

Laboratory evaluations were conducted for 94 weeks to compare, under static conditions, residue levels maintained in water treated with three polyvinyl chloride pellet formulations of fenitrothion. The results showed that foamed formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + ammonium carbonate + citric acid + water + fenitrothion) gave the highest rates in the percentage of fenitrothion released followed by expanded formulation (polyvinyl chloride + dioctyl phthalate + Triton X-100 + fenitrothion), while non-expanded formulation (polyvinyl chloride + dioctyl phthalate + fenitrothion) gave the least.

The records indicated that increasing both the exposure time of formulations tested into the water and the percentage of active ingredient in the present formulations increased the amount of fenitrothion released from these formulations. However, all tested formulations gave low-initial rate of release.

The results showed that there were two rates of release of fenitrothion. In the first step, the non-expanded formulation gave a slow rate of release, expanded formulation gave a moderate rate of release, and foamed formulation gave a fast release. In the second step, the release rate of fenitrothion was slow for all tested formulations.

The life history of Amblyseius fustis (Pritchard and Baker) was studied in the laboratory at a fluctuating temperature and relative humidity ranging from 24.4 to 28.0°C and 55.5 to 75.6%, respectively. The developmental stages consist of egg, larva, protonymph, deutonymph and adult. The life cycle, from egg to adult of both male and female was about 8 days, while longevity was about 19.2 days. Mated female laid an average of 18.8 eggs. There was no significant difference in the longevity and fecundity of predators fed on different life stages of the host. The proportion of male to female in the progeny of mated females was 1:4.

A. fustis has a shorter developmental period and lives longer than its prey, but the latter is more fecund (26.9 eggs/♀) and has a higher proportion of females in its progeny (1:4.8). The shorter developmental period and the longer life span of the predator are likely to offset the higher fecundity of the prey.

The amount of free amino acids increases during the larval development. The accumulation is greater during the later larval life followed by an abrupt decline in the defaecating larva and early prepupa. The overall decrease in the free amino acid content during the period of metamorphosis is more in case of drones in comparison to that in workers. However, the amount present in adult drones is less than that of workers. The changes in the free amino acid content during the post-embryonic development of workers and drones of Apis cerana indica seem to show sexual dimorphism.

Factors contributing to host plant resistance in sorghum to Chilo partellus (Swinhoe) were studied. Oviposition on the plants in the field started 3 weeks after germination and peaked 2–6 weeks later. Egg batches (96.1%) were laid on the leaf blades compared with 3.9% on the leaf sheaths. On the leaf blades, significantly more egg batches were laid on the upper (57.2%) than on the lower leaf surfaces. In young plants, leaves attached to the upper and lower segments were preferred for oviposition, while leaves in the upper segments more or less maintained their share of egg batches over time; there was a shift from the leaves in the lower to those in the middle segments with the plant age. Differences among sorghum lines for oviposition were significant and these lines were divided into three categories based on their levels of oviposition.

Sorghum plants reacted to insect feeding in the stem by production of a red staining compound which did not significantly affect the development of the insect. Four damage symptoms were observed and these were related to different plant ages. Plants compensated damage by the production of extra tillers, some of which produced panicles that were ready by approximately the time of harvest. Plants infested 2 weeks after germination produced maximum tillers and juvenile panicles; and also had the least effective tillers, plant heights and grain yields. Grain yields were depressed in the infested plants for the cultivars tested, except in LC 119/80–3 where there were actual grain yield gains.

Leaf-feeding and ‘dead heart’ scores, which were related to reduced plant heights and yields in some of the cultivars tested, are proposed as rational indices for susceptibility ratings and monitoring of crop losses.

The effectiveness of Bacillus thuringiensis var. galleriae HD-129 against the moths and egg masses of the cotton leafworm, Spodoptera littoralis, has been demonstrated in laboratory experiments. The longevity and egg production were significantly affected when the moths were fed on a sucrose diet containing 17.2 × 103 IU of the tested formulation/mg or higher rates. At lower concentrations (4.4−8.7 × 103 IU/mg), the females gave normal egg production, but the longevity was adversely affected. Investigations show that a formulation with spores alone affects the egg production and hatching, while a formulation with active crystals alone had no effect on egg production. Sprays of B. thuringiensis combined with sucrose on flowering cotton plants seem to affect the biology of the moths released on it. Egg masses sprayed with B. thuringiensis hatched normally, but the survival of the hatched larvae was reduced when treatment was made shortly before egg hatching. Based on the results obtained, B. thuringiensis showed a promising effect in the control of the moth S. littoralis as well as an ovicide larvicide agent.

Bruchidius atrolineatus (Pic) is present in crops of Vigna unguiculata towards the end of the dry season at the beginning of September when pods start to form. Females lay many eggs on most available green pods. However, this oviposition behaviour results in an important egg mortality. During September, pods gradually reach maturity whilst new pods are formed. Females therefore have at their disposal a growing number of differently mature pods. Confronted with such a situation, B. atrolineatus females show an opportunist behaviour and lay most of their eggs on the most abundant stage, i.e. the most easily discovered stage (ripening green pods in mid-September or dry pods towards the end of September). However, they also lay eggs on other phenological stages no matter how abundant they are. B. atrolineatus females therefore show a certain behavioural plasticity enabling them to reproduce on all stages of pods whose maturity, chemistry and texture may differ. Larvae can develop either in maturing or dry seeds. The number of eggs laid from mid September is lower and lower whatever the phenological stage attacked. This decrease would be due to a reduction of the first generation adult bruchids and of the reproductive potential of females.

Callosobruchus maculatus appears in crops at the same time as B. atrolineatus, but oviposits preferentially on dry pods. Eggs are observed during the whole period of study, but the numbers laid are always low. With the increase in pod number, eggs are dispersed among the different substrates available. However, the average number of eggs laid on the pods remains constant. Despite the high mortality due to the oviposition behaviour of B. atrolineatus and to other factors (impact of hymenopterous parasitoids), these two bruchids cause important losses to seeds of V. unguiculata. Control methods against these pests should be envisaged in the field before harvesting.

A survey of the natural enemies of the main malaria vector in Kenya, Anopheles gambiae Giles, revealed the occurrence of a fungal pathogen in field populations of mosquito larvae. Light and scanning electron microscopy was used in the examination of sporangia of the fungus in determining its identity as Coelomomyces indicus Iyengar (Order: Blastocladiales; Family: Coelomomycetaceae). The resting sporangia were found in the thoracic and abdominal cavities of the larvae. A mortality of 63% or higher was found to occur among the larvae of A. gambiae in a two season observation along the Kenyan coast. The authors stress the need for more intensified ecological and laboratory studies aimed at developing C. indicus as a biocontrol agent.

The larvicidal activity of the pathogen Bacillus thuringiensis H-14 against mosquito larvae of Aedes aegypti (L.) and Culex pipiens L. has been evaluated.

The results showed that the susceptibility of culicine larvae to this pathogen was closely correlated with mosquito species tested and its larval instars. The toxicity curves indicated that the serotype H-14 had a higher pathogenicity against A. aegypti than C. pipiens. LC50 values showed that, for both mosquito species tested, the second instar larvae were more susceptible to the pathogen used than the fourth instar larvae.

Apart from lethal action, larval treatments with B. thuringiensis H-14 led to a decrease in the reproductive potential of female mosquitoes that emerged from these treatments.

The influence of resistance or susceptibility of certain maize genotypes on Chilo partellus colonization was studied. The aspects studied were: oviposition in relation to date of planting, plant age and certain morphological and biochemical characteristics. The pattern of oviposition was similar among the maize genotypes and among the different planting dates. However, the intensity of oviposition differed among the maize genotypes and also with plant age. Plants in the whorl stage of development were the most preferred for oviposition. On the whorl-stage plants, ca 92% of all the eggs were deposited on the lower leaves (1–4 from the ground). As the lower leaves senesced with plant age, the upper leaves were selected for oviposition. On all leaves, the lower surfaces were more preferred. The plant characters that appeared to influence oviposition included plant exudates (as the moth diet) and leaf surface trichomes. The quality of exudates from the different genotypes appeared to influence moth fecundity and longevity, while the trichomes appeared to influence the selection of oviposition sites. The possibility of interactions between these factors and oviposition is discussed.

Recent entomological surveys in the Bouaflé sleeping sickness focus of the Ivory Coast have revealed that Glossina tachinoides is considerably more widely distributed than hitherto. Some flies were found in the fringing riverine forests of tributaries of the River Marahoué. However, the greatest concentrations were found in villages and settlements where domestic pigs were kept. The southern limit of G. tachinoides now appears to lie one half degree of latitude further south than that reported by earlier investigators. The authors think there is good evidence that G. tachinoides is extending its range eastwards and southwards through and beyond the Bouaflé area, and the epidemiological significance of this is briefly discussed.

Eggs (1, 2 and 3-day-old), larvae (early and late) and 4-day-old pupae of the rice moth, Corcyra cephalonica (Stainton), were treated with 60Co gamma-radiation at doses from 0 to 100 krads. Evaluation of moth radiosensitivity by the survival of treated eggs, larvae and pupae led to the following sequence of stages in order of increasing radioresistance: for the eggs, 1, 2 and 3-day-old; for larvae and pupae, early larvae (5 days after hatching), late larvae (5 days before pupation) and 4-day-old pupae. Twenty five kiloradians was found to be the most likely unit for disinfestation by radiation of C. cephalonica.

The ovipositional responses of the stem-borer, Chilo partellus, to the susceptible maize genotype, inbred A, are higher than to the resistant genotype, ICZ1-CM. These responses are elicited by certain characters of the plants that are perceivable prior to the moths' arrival on the plants (distance-perceivable) as well as those perceivable after arrival on the plant (contact-perceivable). Distance-perceivable characters were not found to be responsible for the differences in the oviposition on the two genotypes tested.

The contact-perceivable characters of the two genotypes differ markedly in eliciting oviposition by moths. Contact with the resistant ICZ1-CM elicits much less oviposition than with the other genotype.