Continuous trapping of aphids for 13 months in 1985–1986 in a citrus orchard at Kikambala, Kenya coast at an altitude of 15 m indicated that Toxoptera citricida was present in citrus throughout the year. There was a marked seasonal periodicity of flight of alate aphids as shown by two distinct peaks in population density constituting about 72% of the total catch of aphids for the 13 month period. Effect of climatic factors on population levels of aphids is illustrated. Rainfall was found to have an indirect effect on aphid population increase. The negative binomial distribution fitted very well the spatial distribution of the aphids in the field and provided an explanation of the patchy spread of tristeza disease in the citrus orchard at Kikambala. The possibility of reducing the rate of spread of citrus tristeza virus in the field is discussed.

Third instar larvae of Spodoptera litura (Fab.) treated with polyhedrosis virus at dosages above 3.2 × 107 polyhedra inclusion bodies (PIB)/ml produced over 90% mortality. The LC50 was 2.3 × 104 PIB/ml. The estimated median lethal time (LT50) was 7.4 and 6 days at the lowest and highest dosages, respectively.

Polyhedra were observed in the epidermal cells, tracheal matrix, muscles and all nuclei of tissues of the virus treated larva 48–72 hr after treatment.

The density responsiveness of larvae and adults of Cheilomenes lunata (Fabricius) preying on Aphis craccivora Koch was investigated under laboratory conditions where temperature and relative humidity were uncontrolled and fluctuated between 24–30°C and 43–90% respectively. The feeding rates of C. lunata were positively correlated with the population density of prey. The number of prey consumed daily by each predator stage tested, increased more steeply at lower, than at higher prey densities, exhibiting thus the Type II functional response. Fecundity of C. lunata females also increased to a plateau with increasing prey density.

Coffee canopy damage studies with the yellow-headed borer, Dirphya nigricornis Olivier were conducted on mature plants. Single borer infestation of the pest in coffee plantations were established. Age-induced destruction of the coffee canopy was evidenced by the withering of branches, stems and nodes and were correlated to larval developmental days 0–260. Larval frass excretion was immense being 16,214.91 and 12,076.90 g for female and male beetles, respectively and represented direct physical damage by the pest to plants. Analysis of accumulated data of physical measurement on coffee yield components in the three categories of canopy partitions relative to height of the stem above the ground showed that damage to plants by the pest adversely affected them. Generalized non-linear equations relating berries, pinheads, flowers and leaves (P = 0.05 to P = 0.001) to heights of canopy partition above ground level are described. The physical model developed approximates the responses of the canopy to infestation by the beetle, and shows that these were either depressed or enhanced depending on whether the yield components measured were in the bottom, mid or top partitions of the canopy. Threshold damage constants for leaves (0.34), berries (0.41), pinheads (1.54) and flowerbuds (1.07) which caused variability were established.

The feeding habits and infestation of the bitterleaf weevil, Lixus camerunus Kolbe, were investigated in Rivers State, Nigeria. Vernonia amygdalina was the only species preferred for feeding and oviposition by adult L. camerunus, among the species (Talinum triangulare (Jacq.) Wild, Telfairia occidenlalis Hooker fil, Amaranthus hybridus L., Solanum melongena, Capsicum sp., Chromalaena odorata (Eupatorium odoralum) L., Emilia praetermissa L.) associated with V. amygdalina in farms, that were offered. There was a significant correlation between dry weight of foliage consumed and weight of males and females.

Initial tunnelling direction by larvae was upwards, but on the death of shoots, larvae reversed direction and moved downwards along old tunnels. However, newly-emerged larvae in leaf petioles, tunnelled downwards to the main branch, before pursuing an upward course. In addition to main tunnels, there were also branch tunnels. There was a significant negative correlation between length of tunnel and stem diameter. There was a significant negative correlation between gall/stem diameter ratio and stem diameter.

L. camerunus is widely distributed in the State.

The tsetse, Glossina morsitans morsitans, has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three recognizable functional zones: the distal, intermediate and proximal regions, which are characterized by three distinct cell types: I, II and III respectively. The three cell types had numerous microvilli and basal infoldings: the microvilli of type I and II cells were associated with long mitochondria, while those of type III were devoid of mitochondria. Autoradiographic observations using (3H) glucose indicated that there was synthetic activity in the tubules, and that there was greater incorporation of the radiochemical in the distal and intermediate tubule regions than in the proximal region. The distal and intermediate regions have some functional similarities. With regard to primary urine formation in the tubules, it is suggested that the cell types I and II (and hence the distal and intermediate regions) are secretory, and the cell type III (that is, the proximal region) is absorptive. “Canaliculi” in the proximal region increase the surface area for absorption.