The synthetic sex attractant of the pink bollworm of cotton, Pectinophora gossypiella (Saund.) (Lepidoptera, Gelechiidae), is a mixture of (Z, Z) and (Z, E)-7, 11-hexadecadien-l-ol acetate, referred to as gossyplure (Hummel et al., 1973). Field trials in the Lower Shire Valley, Malawi, have shown that of various mixtures tested, 55–60% of the (Z,Z) isomer in a mixture of the two acetates gives maximum field attraction. The catches of both pink bollworm males and males of the red bollworm of cotton, Diparopsis castanea Hmps., in pheromone traps are not affected by the release of mixtures of the pheromones of both species together. Dual-purpose sex pheromone traps may therefore be used to monitor both pest species at the same time. A simple omnidirectional flat disc trap is as efficient in trapping pink bollworm males as more complex designs. Release of gossyplure from a sealed 2·5 ml polyethylene vial or from a Zoecon beem-polyethylene vial is more efficient than from narrow-bore teflon capillary. Presence of the antioxidant 2,6-di-tert-butyl-P-cresol at 8·4% w/w gossyplure does not increase the attractive life of the pheromone in the field. Considerable numbers of the Angoumois grain moth Sitotroga cerealella (Ol.) (Tineidae), together with a new species of gelechiid, were occasionally caught by gossyplure lures in cotton fields. Catches of pink bollworm are not influenced by moonlight or trap colour but are significantly influenced by trap area. Maximum catches of males occur between midnight and 04.00 h in June and between 01.00 and 05.00 h in August.

The larval habitats of Culicoides species were determined by examining a total of 1 476 samples collected from different ecological environments in various parts of Kenya. Immature stages were collected from suspected breeding habitats and adults were reared. Adults were also captured in emergence traps and then identified. To determine species preferences, if any, the materials yielding Culicoides were analysed for pH, organic matter and water content.

Fifty-seven percent of the samples yielded a total of 26 species of Culicoides. Sites in which Culicoides occurred were classified into eleven habitats grouped into four major systems, namely, aquatic, transitional, terrestrial and general systems. Most species were found breeding over a wide pH range in sites which were wet at least part of the time. A few species appeared to select breeding habitats with a high organic content.

The roles of cattle and alternative hosts in maintaining the immature stages of Amblyomma variegatum (F.) and Rhipicephalus appendiculatus Neum. are unknown. Weekly collections of ticks from cattle in two herds in Zambia indicated an apparently higher nymph-adult ratio in the annual totals for A. variegatum than for R. appendiculatus. The larva-nymph ratios for these herds were estimated by a patch-sampling method in which all larvae and nymphs on 100 cm2 areas on the cheek, neck, dewlap, shoulder, ribs, abdomen and lower-foreleg were collected. The overall annual ratios of larvae to nymphs on the two herds were: A. variegatum 5:1 and 14:1, R. appendiculatus 1·5:1 in both herds. The ratios suggest that cattle themselves feed larvae of A. variegatum in sufficient numbers to maintain their nymphal infestation level. The numbers of cattle-fed larvae of R. appendiculatus may not be adequate for this, and alternative hosts may play an important part in maintaining the population at existing levels. There was negligible evidence of significant shift of distribution of the immature stages over the body with advancing season, and it is suggested that patch-sampling affords a method of quantitative comparison of the relative infestations by the immature stages of ticks.

The parasitic larvae of two species of water mites were studied on resting and biting Anopheles implexus (Theo.) from the Zika Forest near Entebbe, Uganda. Details are given of the mites' morphology, positions of attachment, growth stages and visible effects on hosts. Living larvae of the more numerous mite species (designated as species F, Limnesiidae) were only moderately reliable indicators of the nulliparous state of female hosts, whereas those of the other species (species G, Arrenuridae) were more reliable nullipar indicators, evidently owing to their far more rapid development. The presence of living larvae of either species not completely full-grown denoted the nulliparous state of female hosts with certainty. Male mosquitoes showed consistently lower infestation rates than females from the same resting samples, but the incidence of the different growth classes of species F indicated that these mites departed from hosts of either sex with equal facility and therefore regardless of whether the hosts returned to oviposition sites or not. Frequency distributions of species F on each host sex fitted most closely to highly clumped negative binomials, and biological interpretation of patterns of decline in mite numbers on females in successive Sella's stage groups, and other data, provided evidence of there being at most a negligible amount of mite-mediated host mortality.

The study confirms the usefulness as well as the limitations of the presence of parasitic water mites as a rapid means of age-grading female mosquitoes, and suggests several new applications.

The synthetic sex pheromone (dicastalure) of the red bollworm of cotton, Diparopsis castanea Hmps., in Central and Southern Africa, and an inhibitor of male sexual attraction (trans-9-dodecenyl acetate,=IIA), were used in an enclosed 0·2 ha cotton field-cage to reduce successful female matings. Over one month dicastalure at 21·0 and 42·3 g/ha produced average reductions in mating of 47·9% and 72·5% respectively and 37·9 g IIA/ha produced an overall reduction in mating of 71·5%, or 79·5% in released moth populations, over the same period. The proportion of virgin females present in disruption situations was significantly greater than in untreated populations and was density-independent for moth populations of up to 2 200/ha. The proportion of fertile eggs in disruption situations was correspondingly reduced to 30·2% from an average of 67·9% in control cycles. Reduction in sex pheromone trap catches is an unsatisfactory indicator of the extent to which males are prevented from inseminating females and considerably over-estimates the true degree of disruption. This is the first time that a naturally occurring inhibitor has been used successfully to disrupt mating in a field population of insects and it indicates the potential of the method for the control of high density pest populations in cotton. However, use of polyethylene dispensing mechanisms similar to those used in the field-cage disruption experiments would be unsuitable as a practical method of dispensing behaviour modifying chemicals and it is suggested that, for suitably controlled release of such chemicals, currently available microencapsulation technology offers the best prospects.

The four components of the synthesised sex pheromone of Diparopsis castanea Hmps. are dodecan-1-yl acetate (I); trans-9-dodecen-1-yl acetate (IIA); 11-dodecen-l-yl acetate (IIB); and trans-9,ll-dodecadien-l-yl acetate (IV). Increasing the proportion of IIA in a I/IIA/IIB/IV mixture progressively decreased male excitation in a laboratory bioassay, whilst in the absence of I all concentrations of IIA tested were equally inhibitory. The synthetic combination of 80% IV (93% trans: 7% cis) and 20% IIB (=dicastalure), was 485 times more potent in eliciting male activity than a female sex pheromone gland extract. Reduction in male response to crude extract occurred through exposure of males to glandular IIA and through reduced pheromone volatility caused by extracted triglycerides. Maximum quantities of pheromone were detected in the female sex pheromone gland 6–12 h into scotophase and for at least 30 min into photophase. Significantly greater bioassay responses were elicited by the optimal field combination of 80% IV and 20% IIB than for other ratios tested. Excitation and clasper extension were observed in response to the non-attractive IIB moiety and this indicates a role in close-range mating behaviour for this component. The threshold level of male response was estimated to occur in response to sex pheromone at an aerial concentration of 9·2 molecules IV mm3/s−1. This suggests that aerial concentrations of 102–103 times the male threshold response level may be sufficient to cause successful communication disruption in the field. The problems of relating the non-oriented responses in an assay of this type to directional responses in traps are briefly discussed.

Topical applications of a juvenile hormone (JH) mimic induced and prolonged the mature larval diapause of the southwestern corn borer, Diatraea grandiosella Dyar. The onset of this diapause is marked by an ecdysis from a spotted to an immaculate morph. A high percentage of spotted non-diapause larvae treated with a single dose of a JH mimic moulted into the immaculate morph and became dormant. Similar treatments of diapause larvae led to a reversion to the spotted morph, but the larvae remained dormant. These results imply that diapause larvae contain an intermediate JH titre. A use for JH mimics in disrupting the seasonal phenology of pest insects with larval dormancies is suggested.

The suggestion that mosquitoes can discriminate ABO blood group status in man was re-examined and an attempt made to determine recognition mechanisms.

Host choice was assessed in the laboratory by recording landings on and blood-meals taken from the forearms of pairs of human volunteers in a 10-min exposure to 20 females of species A of the Anopheles gambiae complex, and an alternative procedure, which did not involve mosquitoes probing the host's skin, was developed and evaluated. The presence of weals on the host's skin was found to be an unreliable indicator of probing or feeding activity by mosquitoes. The effect of thermally induced sweating was also investigated.

No effect of ABO blood group status on host choice was found. Mosquitoes did, however, show a highly significant preference to land and feed on a subject when thermogenic sweating was induced. Secretor substances in the sweat did not influence host selection.

The predictive value of host variables such as MN blood group, skin temperature and humidity, skin colour and forearm hair density in determining host choice was examined. Very little of the observed variation in mosquito activity could be accounted for by these host variables within the ranges used.

Variation in temperature affected the developmental periods of eggs, larvae and nymphs of Rhipicephalus appendiculatus Neum. and developmental periods were shortest at an optimum of 30°C. The periods increased as temperatures diverged from the optimum until upper and lower temperature limits were reached, when metabolism ceased. These limits were 16°C and 34°C for eggs, and 12°C and 41°C for larvae and nymphs.

Generally, relative humidity did not affect the rate of development. It did, however, critically affect survival, particularly of eggs and larvae. The relative humidity range of 60–70% was critical, and below this range survival of the eggs and larvae was very limited. Nymphs and adults were more resistant, and natural tick populations probably survive hot and dry seasons in these stages.

It was found that in a habitat with thick vegetation, temperature and humidity fluctuations were smaller than in one with sparse vegetation, and the former therefore supported a greater tick population. Denying cattle access to this thick vegetation or getting rid of it altogether seem to be possible methods of reducing the tick load of cattle in the area studied.

D-glucoascorbic acid in 0·05–0·30% aqueous solution fed to adult males of Spodoptera littoralis (Boisd.) caused the production of deformed spermatophores. During mating the spermatophore corpus did not become inflated and permanent copulations were often observed. The inadequate moulding of the spermatophore was caused exclusively by oral uptake of D-glucoascorbic acid in male moths. This ascorbic acid analogue did not affect adult longevity, number of spermatophores or egg fecundity. Moths feeding on an aqueous diet of 0·3 % of this chemical were completely sterile. Bait-stations containing this material might possibly be used to induce sterility in the natural insect population.

A pheromone trap fitted with an automatic recording device to separate hourly catches of males of Phthorimaea operculella (Zell.) is described. Field experiments in Cyprus showed that when the trap was baited with virgin females peak catches occurred shortly before or 1–2 h after sunset; catches increased with wind speed in the range 0·1—4·7 ms-1, decreased with higher relative humidities in the range 62–92%, and were not affected by temperature.

Saliva was obtained by applying capillary tubes to the mouthparts of the cattle tick, Boophilus microplus (Can.), after the subcuticular injection of pilocarpine hydrochloride. Acid-lipid extracts of this saliva showed prostaglandin (PG)-like activity on bioassay. Chromatographic studies confirmed this activity as being due to PGE2. Extracts from homogenates of B. microplus larvae and salivary gland tissue also showed prostaglandin-like activity. A role for PGs in B. microplus feeding mechanisms is discussed.

The night resting sites of Glossina palpalis palpalis (R.-D.) were observed in a riverine swamp at Bara, Bauchi Emirate, northern Nigeria. The flies were marked with an ultra violet reflecting paint and released at dusk. They were detected with the aid of an ultra violet light beam. Most of the flies (72%) rest on leaves (50% on the upper sides) and on small twigs and creepers (20·2%). The average resting height was highest in the mid-rains (3·78 m), dropped in the late rains (2·95 m) and was lowest (1·52 m) in the dry season.

The resting site heights ranged from ground level up to 18 m. Females were found to rest slightly higher than males and when the moon shone both sexes had a tendency to perch higher. It was shown that the night resting behaviour of G. palpalis is favourable to the application of residual insecticide deposits from the air because most of the spray drops are deposited on leaves.

Only a very strong dose of 0·5 mg of hempa caused necrosis in testes of Locusta migratoria (L.). The apical cells, spermatogonia and primary spermatocytes became pycnotic and the germ cells were disorganised. Multinucleated cells also developed, due to failure of spindle formation, and a few hypertrophied spermatids occurred. In ovaries the chromatin of the follicular epithelial cell nuclei was abnormally fragmented; nuclei of the follicular epithelial cells became pycnotic; germinal vesicle was badly damaged; cytoplasm of the follicular epithelial cells was drawn into the peripheral empty space formed by the contraction of the ooplasm; the follicular epithelium degenerated later; and yolk formation was inhibited. With increased doses and post-treatment periods necrosis became more marked. Hempa was more effective in the ovary than in the testes of L. migratoria.

Two techniques have been developed to investigate the incidence of multiple feeding by mosquitoes. One system detects the ABO blood group substances and can be used up to 24 h after feeding in the case of Anopheles stephensi List. and 30 h for Aedes aegypti (L.). It is limited by cross-reactions which develop between blood group substances as digestion occurs in the stomach of the mosquito. The second system detects the serum protein haptoglobins (Hp) and it is possible to detect the Hp type of blood in single feeds 20 h after feeding for Ae. aegypti and 16 h for A. stephensi. Multiple feeds taken within a short time of each other can be identified up to 16 h after completion of the meal. The minimum amount of blood necessary to effect an identification in a fresh two-part meal is 0·1 mg, which is approximately one-tenth of the total amount of blood taken. It is now therefore possible to measure multiple ‘cryptic meals’ taken from man, if they are of different Hp types. Identification of Hp from A. gambiae sp. A blood-meals has been successfully carried out using material sent from the tropics. Limitations of the techniques as applied to field collections are discussed.

The oligophagy of the African armyworm, Spodoptera exempta (Wlk.), was investigated experimentally. The resistance to feeding on cassava, a non-food plant, declined at a faster rate if the larvae had been reared on artificial diet. If diet-reared larvae were allowed to feed on maize for increasing periods of time the subsequent rejection of cassava increased accordingly. This effect could still be induced after removing the labral or palpal sensilla but not after removing both pairs of stylo-conic sensilla. The left and right pair of styloconic sensilla are supplementary to each other. In so far as aversive responses to non-food plants are concerned, the rearing on artificial diet can be considered as a case of pseudomaxillectomy. It is suggested that during feeding on maize the larva receives a specific input pattern which influences central acceptance-rejection decisions in a time-dependent manner. This specific information is absent from artificial diet and can no longer be perceived by larvae without styloconic sensilla.

The distribution and spread, interrelationship with other animals, and economic importance (mainly domestic) of Anoplolepis longipes (Jerd.) in Mahé, Seychelles, after its accidental introduction about 13 years ago, are described. Temporary control measures based on solid and liquid baits formulated largely from local materials were devised. Baits containing aldrin at 2·5% a.i. and applied at 10 kg (solid) and 20 kg (liquid)/ha decreased the abundance of foragers for about 50 days after treatment. Other insecticides tested were less effective. Bendiocarb (0·04% a.i.) sprayed onto walls of houses and buildings provided protection for about a week outdoors, and for up to two months indoors. There are good prospects for the eventual decline and stability of populations of this ant on Mahé.

Large numbers of adult Austrosimulium pestilens Mack. & Mack, appear about a week after floods in permanent and temporary waterways and, because of the short period when stream flow remains suitable for oviposition, mating, feeding and egg maturation take place near the river where they breed. Most flies emerge early in an outbreak and fly to mating swarms at trees beside or near the river. After obtaining a blood meal from any of a number of mammal species nearby, females return to 1–5 m tall trees at the river's edge to mature their eggs in an unusually short time of 24 h. Although this species prefers rapidly flowing water, immatures also survived in trickles remaining after floods had passed, though the resulting adults took longer to develop and were smaller than normal. The closely related A. bancrofti (Tayl.) lives in more permanent waterways and disperses away from its breeding sites soon after emerging, concentrating in highest numbers on hills as far as 10 km or more from its nearest major breeding site. Catches in CO2-baited traps were influenced by temperature, wind, light intensity and rain. Although A. pestilens bit man and many mammals, A. bancrofti did not bite any vertebrate tested. In CO2-baited traps where man was present, there were large fluctuations in the catch of A. pestilens from minute to minute, while the catch of A. bancrofti decreased steadily.

The effect of host movement on multiple feeding by Aedes aegypti (L.) was observed in a laboratory experiment and the value of techniques developed to measure multiple meals was assessed. Multiple feeding on the arms of two human volunteers was significantly increased when both hosts moved their arms. If only one host was moving, a slight increase in multiple feeds over the level obtained with no movement was noted, although in such cases the majority of meals were taken from the stationary host. Statistical analyses of the results showed that the association between host movement and multiple feeding was highly significant.

Three plant spacings, 30 cm, 7·5 cm and 2·5 cm within rows 90 cm apart, equivalent to about 36, 143 and 430 thousand plants/ha respectively, were used in three field trials on the population dynamics of Aphis craccivora Koch on groundnuts at Chitedze, Malawi in 1964–1967. Aphid density per infested plant was consistently higher, while numbers of aphid-infested plants per unit area were consistently lower, in 30 cm than in 2·5 cm spacing. Aphid numbers per unit area increased to similar levels at all spacings in crops under 40–50 days old, but subsequently aphid density was consistently lower in 2·5 cm than in 30 cm spacing. This effect could not be related to the intensity of fungus disease infection, parasitism, predation, the availability of feeding sites or the rate of emigration. Aphid groups were, however, consistently smaller in 2·5 cm than in 30 cm spacing in one trial. The potential rate of increase was studied in two trials using the methods of Hughes (1962), and was found to be consistently lower in 2·5 cm than in 30 cm spacing. The rate of plant growth was relatively depressed in 2·5 cm spacing, particularly after 40 days. The effect of spacing on aphid numbers was attributed to the effect of host-plant condition on the potential rate of increase.