The LC50 values (% active ingredient in parentheses) for 34 formulations of 29 insecticides, obtained by dipping green berries (GWB) infested with adult Hypothenemus hampei, were: thiodan EC 35 (0.0003) > perfekthion (0.0004) > carbicron (0.00044) > decis (0.0005) > actellic (0.0008) > basudin (0.0009) > belmark and ciodrin (0.0012) > thiodan EC 3 (0.0013) > malathion (0.0014) > folimat and bidrin (0.002) > aldicarb and lindane (0.003) > nexion > tiovel EC 3 > dursban (0.0046–0.006) > supona > methomyl > kelthane (0.011–0.012) > chlordane > aldrin > dimilin > chlorfenvinphos > phosdrin > sevin > methoxychlor > dieldrin (0.016–0.025) > nexagan (0.034) > azodrin (0.04) > fenitrothion (0.07) > bimarit (0.14) > chlorpyrifos (0.39) > gardona (0.96).

The order of toxicity remained the same for borers in the pulp (GP) or endosperm (GE) of green berries or endosperm of red (RE) berries, though the LC50 of each formulation of the same or different insecticides varied significantly. The respective LC50 values for the four leading, and the rest of the formulations were about 7−21- and 2−6-fold higher in GWB than GP, 9−23 and 2−5-fold higher in GE than GP, 1−2.3- and 1−3-fold higher in RE than GE, and 12−25- and 3−37-fold higher in RE than GWB. The practical significance of the results is discussed.

The structure and function of the male accessory reproductive gland system of the cotton stainer, Dysdercus fasciatus Signoret, was studied using ultrastructural techniques. The gland system is composed of a pair of mesadenia and an ejaculatory duct, whose anterior end is swollen and encloses a glandular structure whose origin is not clear. Each mesadene is composed of a large number of sacs whose lumina are confluent. The epithelium of each sac is one cell layer thick and is composed of two cell types, mononucleate and multinucleate cells. The origin and siginficance of the multinucleate condition in the mesadenial epithelial cells is not clear, but it is suggested that this condition might have arisen during maturation, when mitotic divisions are complete, but the nuclei continued to multiply within an increased cytoplasmic mass, which itself does not divide.

Data on the populations of larval and pupal stages of Aedes africanus, an important sylvan vector of arboviruses, were collected from tree-holes which are its natural breeding sites in forests. Comparable data were also simultaneously collected from bamboo pots stationed in the Zika Forest to simulate the natural breeding sites. Survivorship curves and time-specific life-tables were constructed. It was observed that the immature stages of A. africanus in both tree-holes and bamboo pots suffered very high mortality rates (an average of 91% in tree-holes and 83.2% in bamboo pots). It was further observed that mortality rates varied monthly. The survivorship curves constructed for the immature stages collected on a daily basis tended to show that a large proportion of the mortality rate was confined to the early instar stages, but the survivorship curves based on the combined data for the 2 years indicated constant mortality rates for all the stages. The high mortality rates of the immature stages of A. africanus appear to be attributed to predation by larvae of Toxorhynchites brevipalpis, with which it shares the same breeding places.

The sorghum shootfly was first recorded as a pest in the central rainlands, causing losses of up to 25% in local varieties and 25–62.5% in introduced varieties. The pest has also been recorded in the Northern, Khartoum and Equatorial provinces.

In the Sudan, more than one species of Atherigona attack cereals, Atherigona soccata being the most dominant species. Sorghum plants attacked by the shootfly flower and ripen at different times.

A study of the biology of the shootfly showed that the incubation period of the egg was 2–3 days, the pupation period was 6–8 days and the duration from egg to adult was 17 days. The closer the eggs were laid to the leaf blade, the better the chances of the shootfly causing ‘dead-heart’ symptoms. The mortality of the first-instar larva was highest in the first 24 hr. The incidence of the shootfly coincided with rainfall and lower temperatures.

In a selection programme, Combine Kafir 60 had the lowest infestation level, compared to Sudan Grass, Abu Sabein and Feterita Gadarif varieties.

Three morphological classes of haemocytes (prohaemocytes, plasmatocytes and granulocytes) were observed in the haemolymph of Glossina morsitans morsitans and G. pallidipes. In addition to the three types, a category of spindle cells were also observed in haemolymph especially in the newly emerged Glossina. Based on their unusual morphology, as well as on their inverse relationship with the number of thrombocytoids (a filamentous plasmatocyte), it is suggested that these spindle cells might be precursors of thrombocytoids observed mostly in older Glossina. The number of thrombocytoids increased progressively with the increasing age of the flies. Total haemocyte counts (THCs) dropped significantly during the first 48 hr following emergence, after which the values levelled off with the exception of minor fluctuations. This sudden drop in THCs resulted primarily from a remarkable decrease in the number of the spindle cells in the haemolymph. The number of round plasmatocytes decreased gradually and progressively with age of the flies, while the number of the granulocytes increased, suggesting a possible transformation of plasmatocytes into granulocytes. Newly emerged female G. morsitans morsitans were observed to have significantly higher THCs (P < 0.01) than males of the same age. Although no difference was observed between THCs of 5-week-old pregnant and non-pregnant female G. morsitans morsitans, the differential haemocyte counts (DHCs) showed that the concentration of thrombocytoid fragments was significantly lower (P < 0.01) in the pregnant than in the non-pregnant females.

In Upper Volta the sorghum shootfly is considered dangerous in the case of late and staggered sowing or resowing due generally to irregular rainfall in the beginning of the rainy season. When using fish meal as bait in two different traps, one placed in a humic area and another in a dry area, we followed over a period of 2 years the dynamics of the sorghum shootfly populations at Farako-Bâ. Twenty-two different species of the genus Atherigona (Rondani) were identifed, of which the commonest was A. soccata (Rondani).

Some wild hosts of the sorghum shootfly were also identified. Attention is drawn to the importance of the pest in the case of extensive cultivation of irrigated sorghum in the managed valleys of the country.

Ultrastructural studies were carried out on wild Kenyan sandflies (Phlebotomus pedifer) naturally infected with Leishmania aethiopica. The promastigotes were attached to structures resembling pieces of a peritrophic membrane. They were located amongst long microvilli and also deep in the cytoplasm of the gut cells. The factors which influence the invasion of the parasites into cells are not known and need to be investigated.

The sex-stimulant contact pheromone present in the cuticle of female tsetse Glossina pallidipes Austen has been extracted with hexane, separated by preparative gas chromatography and identified by mass spectrometry. The aphrodisiac, consisting of 13,17-dimethylpentatriacontane and 15,19-dimethylpentatriacontane, is present in cuticular extracts of 1-week-old females and, in lower amounts, in teneral females but it is almost absent in males of all ages. Full copulatory responses to hexane-washed dead males treated with the two dimethylpentatriacontane isomers were induced in 10–20-day-old adult male G. pallidipes. The practical uses to which this discovery can now be put—towards the mass-rearing and control of G. pallidipes— are discussed in detail.

Field and laboratory observations revealed that the placement of eggs of the sorghum shootfly, Atherigona soccata, among sorghum stems tended to be random or slightly aggregated rather than regular, which suggests that the site of oviposition by a female is little or not determined by the presence of other eggs already laid. The possible effects of this type of distribution on the mortality of the first-instar larvae are briefly discussed.

Phlebotomus martini, a sandfly belonging to the Synphlebotomus group, is the main vector of the fatal disease kala-azar in Kenya. The breeding sites of this species have so far remained a mystery, and immature stages have not yet been observed in nature. Collection of adult P. martini was done through human-bait. Immature stages, obtained from these catches, were reared to the adult stage in the laboratory for the first time. The size and the rate of development of the various stages were studied at 27°C and 100% r.h. The mean duration from egg to adult was 56.1 days. Observations were made on the biting behaviour of sandflies during human-baiting. Preliminary observations of natural enemies encountered in the rearing cages are described.

Investigations are reported on oviposition habits, development, and emergence patterns of the pre-adult stages of Aedes (Stegomyia) africanus (Theo.) under laboratory conditions. It was observed that water or at least a wet surface is necessary for oviposition and that the intensity of egg-laying takes place within 2 cm from water surface and is greater in those containers with deeper water levels. Post-oviposition embryonic development lasts an average of 6 days thus conforming with earlier findings (Gillett, 1955). The quantity of water does not affect either the period of post-oviposition embryonic development or the rate of egg hatching. However, an average of 75% of the eggs hatch within the first 13 days after flooding, leaving the rest to hatch in subsequent instalments. At 27°C, the second-instar larvae take the shortest time to develop while the fourth-instar larvae take the longest period. Generally, intra-instar variability in growth rates were observed except in the pupal stage. Emergence of the various pre-imaginal stages and pupation did not appear to have any regular periodicity. Of particular interest was the observation that the number of instars in this species varied from the normal number of four, a finding which is believed not to have been recorded previously in the family Culicidae.

Nutritional efficiency of four dehydrated and powdered tapioca puddings for Tribolium confusum (duVal) was assayed by studying growth, survival and fecundity of the confused flour beetle on these diets.

The common pudding inflicted about 50% mortality and caused over three-fold growth retardation in the larvae. The longevity and fecundity of the adults also were significantly reduced (P < 0.01). On the other three test puddings which contained less vitamins and more fat or carbohydrate than the common pudding, growth was even more severely retarded, and only 9% of the larvae became adults of doubtful reproductive ability. Results obtained from puddings supplemented with vitamins, or made with synthetic milk in which vitamin and fat levels were manipulated, suggest that the nutritional inadequacy of the four test puddings was mainly due to low vitamin and high fat contents.

The results demonstrate the practicality of inducing ‘self-protection’ against insect pests in certain types of food products without seriously affecting their acceptability by man.

Surveys were conducted in two different ecological zones (semi-arid and arid) of Kenya to monitor egg, larval and pupal populations of the sorghum shootfly, Atherigona seccata, on a wild host, Sorghum arundinaceum. Populations were found to be usually higher on wild sorghum than on local varieties of Sorghum bicolor, the cultivated host. During dry periods, shootfly eggs and larvae were still found on wild sorghum, especially in moist areas such as beds of temporary streams or river banks. Population levels seem to be related primarily with the availability of susceptible stems, which in itself is determined by rainfall, soil conditions, density of other vegetation and by the phenology and the distribution of the host plant, Sorghum arundinaceum, being a pioneer species which colonizes recently disturbed areas and is subsequently replaced by other grass species. Since no evidence of the existence of an aestivation diapause has been found, it is reasonable to assume that Sorghum arundinaceum is a major reservoir for A. seccata, especially during the dry season.

The assumption was made that for a complete understanding of the feeding behaviour and nutrition of Atherigona soccata larvae on various cultivars of sorghum, it was necessary to investigate the relationship between plant chemicals occurring in resistant sorghum plants and the digestive enzymes of larvae. However, at least an introduction to the anatomical organization of the alimentary canal of larvae is needed to understand the digestion and absorption of food taken from resistant and susceptible sorghum lines.

The present preliminary investigation was undertaken to determine qualitatively some of the enzymes present in the gut and salivary glands of the third instar by locating enzymes histochemically on polyacrylamide gels.

Observations were made on the tsetse species Glossina longipennis Corti in Nkruman escarpment, Kenya. The species inhabited relatively open areas of the bushland. The rate of infection with trypanosomes was studied as well as the activity pattern and amenability to trapping. Results of laboratory rearing are given. Trypanosome infection rate was higher in female flies than in male ones. The method of using a slow moving vehicle, resulted in the capture of more old flies than young ones—of both sexes—and more males than females. G. longipennis was not amenable to trapping by any of the two mechanical traps used (Moloo's trap, and the biconical trap of Challier and Laveissiere).

Animal-infective forms (metacyclics) of Trypanosoma brucei brucei were grown in continuous culture at 29°C from the salivary glands of infected tsetse. The parasites were found by immunofluorescent staining to be antigenically stable in the course of cultivation. When the antigenically stable parasites were incubated at 37°C they transformed from long and thin forms to short and stumpy ones and finally to long and slender parasites. The latter generated antigenic variants starting from the second, third or fourth week of incubation at 37°C. Once antigenic variants appeared at 37°C it was not possible to restore the parasites back to antigenically stable populations when they were transferred back to 29°C. These findings may have far-reaching implications in the study of antigenic variation in pathogenic African trypanosomes and the possible development of immunizing reagents against tsetseborne trypanosomiasis.

Movement, feeding behaviour and growth of larvae of the sorghum shootfly, Atheriyona saccata, were studied under controlled conditions on a susceptible sorghum variety, CSH-1. The time of hatching coincided with the presence of moisture on the leaf, a condition favourable to movement of the larvae to the base of the leaf. Cutting of the central shoot at its base by the larva caused the symptom referred to as ‘dead heart’. The three larval instars are described and changes in the cephalopharyngeal skeleton discussed.

Movement of the larva to the base is not due to positive geotaxis. Larvae in plants placed horizontally to the ground did not develop normally and a high mortality resulted. The larvae are strongly cannibalistic inside the host-plant but not outside of it. The first-instar larvae do not migrate from one plant to another, but the third instars may do so if the source of food is exhausted.