1. Under laboratory conditions (25 to 27°C), female Cydia ptychora (Meyrick) laid an average of 44 eggs. 2. The egg incubation period was 5 days, while the larval developmental period lasted 7 to 10 days, and the pupal period 12 days. Thus, the total developmental period (egg to adult) lasted 24 to 27 days. The adult longevity averaged 10 days (13 to 15 days). 3. Descriptions of the different life stages and setal maps of the different larval instars are provided.

Examples from recent literature are used to discuss the host location behaviour of tsetse in relation to feeding patterns. Tsetse recognise potential hosts by their visual and olfactory characteristics. These, and mechanical stimulation, will activate tsetse and initiate host-oriented responses. Approach to a stationary host is by upwind flight modulated by olfactory stimuli with visual responses only at short range, while the approach to a moving host is largely mediated by visual input. Non-random feeding patterns, even where host and tsetse occupy the same habitat, may be explained by host responses to tsetse attack. There is little evidence of long range discrimination between hosts. Some epidemiological implications of the resulting feeding patterns are discussed, and the host location behaviour of tsetse is compared with that of other insects including mosquitoes.

The spatial distribution of Cataulacus guineensis F. Smith in relation to shade regimes and also in relation to other ant species is investigated. It was found that the species prefers nesting in areas with continuous shade. It has a significant association with Oecophylla longinoda Latr. and also with Camponotus olivieri (Forel), but has non-significant association with Macromischoides aculeatus Mayr, Crematogaster depressa Latr. and Polyrhachis decemdentata Adre. The colony size of C. guineensis was also studied, and 1 to 3 nests were found to constitute any one colony. Abundance of nests and nest distribution in relation to shade regimes was examined. Observations on the insects in defending their nests are reported.

The existence of phase variation in S. exempta has long been known and the possible significance of the phenomenon in terms of the insect's life-system has been discussed previously (Rose, 1979). Present studies carried out on a comparative basis have shown meaningful differences in many attributes of solitary- and gregarious-phase caterpillars.

The solitary-phase caterpillars take longer to develop, possess more protein fractions and higher levels of juvenile hormone in the haemolymph of sixth instars, and their pupae consume more oxygen compared to the gregarious ones. It is suggested that the solitary form of larvae is the normal type for the species, while the gregarious form is able to make maximum use of resources during some parts of the year.

Mobility of tsetse flies is influenced by various factors including the search for a blood-meal. Field observations on the feeding behaviour of tsetse are difficult. The use of bait animals for experimental purposes may indicate food sources but not host selection under natural conditions. Availability and density of a particular potential host species in a tsetse habitat can influence the feeding habit of the latter. Flies are capable of adapting to new host species in the absence of the usual ones. Host selection might be due principally to availability of host(s) and not based on true preference. Tsetse flies respond to visual stimuli from moving objects. Their shape, colour and size are important factors eliciting visual response. Whether these factors are distinguished separately or in combinations is not clear. Odour emanating from live hosts causes up-wind olfactory response towards the source(s), resulting in actual landing on test targets even when the hosts are out of sight. The components of odour have not been isolated. It is therefore doubtful if host selection can be associated with odour, as this might imply that tsetse can differentiate the odours of the different potential hosts. The difficulties in ascertaining true host selection by tsetse are discussed to stimulate further investigations.

The dwarf variety of coconut, Cocos nucifera L. (Palmae), was found to be eaten by the larvae of the African armyworm, Spodoptera exempta (Wlk.). The comparison of the armyworm infestation on the leaves of the coconut seedlings and the adjacent grass species revealed lower larval density and growth rate on coconut seedlings. This observation suggests that a small population of the African armyworm can survive and develop on the leaves of the dwarf variety of coconut.

Preliminary studies on the life history and behaviour of the legume podborer, Maruca testulalis (Geyer), at Mbita Point on the shores of Lake Victoria have shown that most of the eggs (86%) of M. testulalis are laid on the leaf. Over 90% of such eggs laid on the leaf are oviposited on the lower leaf surface. Most adults were found to emerge between 2000 and 2300 hr. The number of eggs laid per female varied between 6 and 194, and over 72% of these were fertile. No larval or pupal diapause was observed.

Larval duration was 8–14 days and the pre-pupal stage lasted only 12–24 hr. The whole life cycle at Mbita Point was found to be about 20–57 days.

An important factor that previously discouraged detailed studies on the biology of M. testulalis is the fact that the eggs are translucent and extremely difficult to see against the background of the oviposition site. The discovery of these eggs was a major step in beginning to work on this important pest.

Although mating is a necessary prerequisite for the induction of ovulation in the tsetse fly, Glossina morsitans morsitans, neither the accessory gland substance from the male nor any testicular component is responsible for causing ovulation. Experimental evidence suggest that two neural factors, one originating from the uterus during mating act as an afferent stimulus, and the other originating from the ovary during oocyte maturation regulate a cerebral hormonal factor which controls the event of ovulation. It is probable that one successful copulation removes an inhibition for the release of an ovulation stimulating hormone from the neurohemal organ into the circulation. The rate of synthesis and/or transport of the hormone from the neurosecretory cells to the neurohemal organ is probably regulated by the rate of oocyte development.

The pattern of singing activity of Glossina morsitans morsitans was monitored in LD 12: 12. Both males and females showed a clear “U”-shaped diurnal pattern of singing activity typical of other responses in tsetse flies. The morning peak comprised more activity than the evening peak. The significance of sound production and the possible endogenous control are discussed.

A procedure has been developed which allows production of 75,000 eggs per month of the legume pod-borer, Maruca testulalis (Geyer). More than 170 eggs per moth were obtained. The optimal number of moths placed in the mass oviposition cage having potted cowpea plants was 30. The average life-span of the moths was 7.7 and 9.5 days for females and males, respectively. The optimal number of larvae in the rearing box was 50: larval survival declined sharply above a density of 50 per box.

Studies of some vector-borne diseases have shown genetic factors to be involved in the vector–parasite relationships and these results have often influenced measures taken to control such diseases. Novel methods of vector control have emerged from genetical studies, such methods having the dual advantages of being species specific and of causing little environmental damage. However, genetics has made little impact on trypanosomiasis research or control when compared with other vector-borne diseases, for reasons which are related to the biology of the tsetse fly and the trypanosome. Despite these natural limitations, genetical studies may yet provide useful information for those engaged in trypanosomiasis research. For example, chromosome and isozyme studies have shown that there is a large amount of genetic variation within tsetse populations, but it is not known whether such variation is related to the distribution of the disease. The infection rates of flies are known to vary between species and are dependent on fly-trypanosome interactions but it is not known whether these interactions have a genetic component. It is suggested that studies of the genetics of natural populations of tsetse, combined with selection experiments in the laboratory, could provide answers to these questions which might be of importance to control programmes and to studies of the epidemiology of trypanosomiasis.

Population studies of the whitefly, Bemisia tabaci, carried out in the field indicated that whiteflies were present in cassava all year round and that there were marked seasonal fluctuations in the population levels. Possible explanations for these fluctuations are discussed. It was found that the interaction of atmospheric temperature and relative humidity was highly correlated (r = 0.924) with the development of the whitefly. Results of the studies suggested that rainfall has an indirect effect on whitefly population. Whether B. tabaci behaves in the same way in mixed cropping system has not yet been established.

Proteins of male accessory reproductive gland secretions and the spermatophore of the tsetse, Glossina morsitans morsitans, have been characterised by electrophoresis. The spermatophore contains all the major proteins of accessory gland secretions and no new proteins were detected.

Influence of blood meals and neurosecretions on synthesis of accessory gland secretions and insemination are discussed. It is concluded that synthesis of accessory gland secretions commences prior to adult emergence and continues uninterrupted in the adult, independent of the corpus allatum.

The development and morphology of the immature stages were examined by means of dissections, linear measurements, light and scanning electron microscopy of the egg, the larval instars and the puparium.

The measurements were of body lengths and widths and the lengths of the cephalopharyngeal skeleton. Observations on the morphology of the immature stages concentrated on the surface structure of the egg, the head capsule, the anterior and posterior spiracles, the ventral plate and the cephalopharyngeal skeleton of the different larval instars.

Development and survival of larvae at different growth stages of the sorghum plant were investigated in the laboratory. Survival and rate of larval development were dependent on the size of the host plant. Survival was usually highest when plants about 2 weeks old were infected, low in very young plants and lowest in plants more than 50 days old. Within groups of insects hatched from eggs laid on the same day, the occurrence of various larval instars overlapped. The first instar was found from the 2nd to the 8th day after egg-laying, the second instar from the 4th to the 12th day, and the third instar from the 5th to the 18th day. Pupation started on the 14th day and adults started to emerge on the 21st day.

The factors effecting establishment of salivarian trypanosomes in Glossina (tsetse flies) are reviewed. Recent observations on host–parasite relationships are outlined in the trypanosome-Glossma system. These include, in Trypanozoon, the penetration of the peritrophic membrane; the infection of the midgut cells; the finding of cyst-like multinucleate forms in midgut cells; and the observations on haemocoelic stages in laboratory and field studies. The implications of haemocoelic infection are discussed in relation to work on other Trypanosomatidae in insects and the importance of studies on the possible immune mechanisms of tsetse are outlined.

The interaction between trypanosome parasites and the surfaces of Glossina are briefly reviewed. Recent studies on the relationship between salivarian trypanosomes and LC1 and LC2 mechanoreceptors in the labrum are presented, which indicate that trypanosomes could impair receptor activity in different ways which would result in increased probing. The epidemiological and epizootological implications of these suggestions are outlined. The relevance and importance of trypanosome infection rates in Glossina are discussed.

In the course of the in vitro cultivation of Trypanosoma brucei as midgut forms, immature metatrypomastigotes, and metacyclic forms, a phenomenon was observed that suggested possible existence of sexual forms consisting of two parasites of unequal size which were seen to come close to each other with their posterior ends apposed. The smaller parasite which was more active than the larger one travelled along the side of the latter so that its posterior end came to lie in the region of the kinetoplast of the larger one. At the latter site, the smaller parasite displayed vigorous twisting movements and later came to lie parallel to its partner. Electron-microscopic examination of the parasites revealed that the points of contact were the kinetoplast and the flagellar pocket. These observations point to the possible existence of sexual forms, and the transfer of genetic material in the 3 types of T. brucei cultured from the vector, G. m. morsitans.

The phytosterols inokosterone, makisterone A, ecdysterone and ecdysone were effective growth regulators and abortifacients (70%) at estimated doses of 1.4 × 10−4 M, 6.8 × 10−4 M, 5.2 × 10−5 M, and 7.8 × 10−5 M respectively when fed to female tsetse Glossina morsitans morsitans. The sterols, added to defibrinated cow or pig blood, were fed to the flies in an in vitro system through a silicone rubber membrane. Cyasterone and ponasterone A were only slightly effective, therefore the hydroxyl groups on the side chain appear to confer activity. Evidence is presented to support three hypotheses which may be advanced to describe the mode of action of the sterols, namely:

(a) Synthesis and/or release of the ‘milk’ secretion from the uterine gland is significantly retarded.

(b) Although the size of the blood-meal is normal, digestion of the in vitro meal is very slow.

(c) Development of the larva itself may be affected by the presence of the hormonally active sterol (or a metabolite) in the ‘milk’.

Effective dose of sterol causing 70% abortion in flies is very much lower than that dose required when injected into the haemolymph. The Malpighian tubules very rapidly excrete the sterol. Therefore, either (1) a slow release of sterol or metabolite into the haemolymph is necessary to disrupt ‘milk’ production, or (2) digestion of the treated in vitro meal itself (and subsequent meals as well) is so retarded that the larva in utero is effectively starved.

The cyclic transmission of African trypanosomes is subject to the successful passage through successive ‘biological barriers’ associated with the ecology and physiology of the host(s) and vector(s), and the ability of the parasite to adjust to the various substrates. This paper is an analytical compilation of factors which play a relevant role in the complex pathway characteristic of trypanosome transmission. These are discussed under the following headings: (a) physiology of the parasite; (b) physiology of the vector; (c) ecology of the vector; (d) feeding habits of the vector; (e) physiology of the vertebrate host; and (f) behaviour of the vertebrate host.

The goatweed, Ageratum conyzoïdes L., contains the same chromenes, precocenes 1 and 2, as the bedding plant, A. houstonianum. A crude lipid extract from the goatweed exerts ovicidal action and induces sterility after topical treatment of both young last instar larvae (L6) and females of Dysdercus flavidus Sign, at emergence by inhibiting ovarian development. The chromenes survived metabolism for at least 12 days. The action of the two chromenes in the crude extract is synergistic.

The performance of two laboratory colonies of Glossina pallidipes Austen originating from two areas in Kenya, Nkruman in the Rift Valley and Mwalewa forest in the coastal area, are described and compared. Two attempts to rear flies from Nkruman failed. Flies from Mwalewa were maintained with variable success for four years. Difficulties in rearing flies from Mwalewa could be explained by irregularities in the conditions of the breeding room, in contrast to failures in rearing flies from Nkruman. Life budgets were made to evaluate the performances of the colonies. In both Nkruman colonies the highest mortality factor was ‘loss due to non-production’. In the Mwalewa colony the highest mortality was ‘loss due to low production’. The key mortality factors were ‘loss due to low production’ (Nkruman colony A), and ‘premating mortality’ (Nkruman colony B, and Mwalewa colony). Factors which possibly contribute to the difficulties in rearing G. pallidipes are discussed. Flies from Nkruman and Mwalewa differed from each other in copulation time, pupal weight, age at which the first larva is produced, and duration of interlarval periods. The results of this study support the assumption of the existance of population diversity in this species.