Alate exules of Rhopalosiphum padi (L.) were flown in a flight chamber for three different flight times: 1 min, 5 min and 25 min. The rate of climb was recorded continuously during flight. Afterwards, the aphids were forced to land on either wheat or potato and settling behaviour was recorded. The settling response was strengthened with increasing flight time on both plants. The aphids spent more time walking and made more probes on potato than on wheat after 25 min of flight. The rate of climb was the same immediately before landing as immediately after a spontaneous re-take-off, except after a 25-min flight and landing on potato when the rate of climb was significantly higher after re-take-off. Comparison with Aphis fabae Scop. from other investigations showed that the change in settling response with flight time was similar for the two species. R. padi seemed less able to discriminate rapidly between host and non-host plants than A. fabae. It is concluded that its behaviour does not hinder R. padi from being a vector of stylet-borne potato viruses.

The vertical distribution of flying mosquitoes was investigated in separate experiments in open savanna and over a fallow field system near Keneba Village in the tidal zone of the Gambia using suction traps located at seven levels (0·1, 0·25, 0·5, 1·0, 2·1, 3·9 and 7·9 m) on a scaffolding tower. Mosquito density declined progressively with height for Anopheles melas Theo., An. pharoensis Theo., An. squamosus Theo., An. ziemanni Grünb., Aedes dalzieli (Theo.), Ae. punctothoracis (Theo.), Culex tritaeniorhynchus Giles and Mansonia spp. Catches of C. thalassius Theo. and C. invidiosus Theo. increased with height to around 1 m and then decreased steadily although the 7·9–m trap consistently captured more C. thalassius than the trap below, presenting a bimodal vertical distribution profile. Flight altitudes of the two most abundant species, An. melas and C. thalassius, declined as the night progressed, but wind speed and lunar phase had no clear or consistent effects on flight levels. A functional relationship between flight altitudes and dispersal patterns of mosquitoes is suggested.

Three West African strains of Anopheles gambiae Giles were intensively selected for DDT resistance at the adult stage using both mass selection and family selection with inbreeding. The LT50s for 4% DDT were thereby raised to 2–6 h, i.e. 6–18 × that of a susceptible strain. The selected strains were found to show DDT resistance as first-instar larvae and permethrin resistance as adults. The results of tests for the number of genes involved in causing the resistance and their linkage to genes for dieldrin resistance were equivocal. One of the DDT-resistant strains was bred in population cages with overlapping generations. Releases were made of males of the R70 translocation strain which transmit DDT and dieldrin susceptibility to their female progeny. When DDT selection on the cage population was relaxed, the releases caused a more rapid and complete loss of resistance than occurred in a control population. When selection for DDT resistance was applied to females of the cage population, the releases were able to prevent a build-up of resistance. The use of male releases is discussed as a possible means of countering insecticide resistance in mosquitoes.

The distribution of fed mosquitoes in a village in the Gambia where bed nets are widely used was studied. A total of 3470 blood-meals from Anopheles gambiae Giles s.s. and other mosquitoes was analysed to determine the human blood index (HBI). A. gambiae s.s. collected within nets gave an index of 0·99, whereas those within houses but outside nets gave an index of 0·70. The importance of distinguishing biotopes when presenting HBI values is stressed. By using a unique host, mosquitoes were ‘ marked ’ (with a blood-meal) and their dispersion was studied. Evidence was obtained for movement from house to house and from outside into houses before resting.

Dacus dorsalis Hend. infested eleven, D. cucurbitae Coq. five and D. umbrosus F. two of the eighteen common fruits and vegetables grown in Penang, West Malaysia. D. tau (Wlk.) infested bacang (Mangifera foetida), D. caudatus F. chilli (Capsicum annuum) and D. frauenfeldi Schin. water guava (Eugenia javanica), together with D. dorsalis. Pomelo (Citrus grandis) was found infested for the first time by D. cucurbitae. No flies were trapped using Capilure and trimedlure as baits. Cue-lure attracted D. caudatus, D. cucurbitae, D. frauenfeldi, D. occipitalis (Bez.) and D. tau. Methyl eugenol attracted D. dorsalis and D. umbrosus. Dorsalure was less attractive to D. caudatus and D. dorsalis than cue-lure and methyl eugenol, respectively, but it was equally attractive to D. frauenfeldi as cue-lure. Using traps baited with cue-lure or methyl eugenol in five ecosystems, the highest numbers of males of D. dorsalis, D. umbrosus, D. frauenfeldi and D. caudatus trapped were from a village, on a vegetable farm for D. cucurbitae, and D. occipitalis was only caught in a forest. Analysis showed that for each species of Dacus the difference between ecosystems was highly significant. The few examples caught in grassland were probably migrants.

Field experiments in England with traps baited with allylisothiocyanate (ANCS) showed that females of Delia radicum (L.) were distributed more or less evenly through established brassica crops. Reducing the quantity of ANCS released from the traps either by diluting the concentrate with liquid paraffin or by presenting the concentrate in Wädenswil dispensers reduced the numbers of females caught. There was no indication that ANCS became repellent, even when released at a rate of 24 ml/trap per day. For maximum effectiveness, the ANCS dispenser had to be placed at the centre rather than at the edge of the trap. Attempts to make traps more effective by releasing the ANCS from several point sources around a trap, in the hope that this broader odour plume would ‘ attract ’ more flies, were unsuccessful. The ANCS-baited trap had an effective zone only 5 m in radius.

Flight initiation of adults of Triatoma infestans (Klug) was recorded in a laboratory apparatus. The proportion of individuals initiating flight depended on the nutritional status of the insects, and flight activity was greatest about 12–18 days after feeding. From measurements of the weight and length of the insects, it was possible to assign the probabilities of flight initiation and thus predict the proportion of an adult population likely to fly. The predictive model should be of use to field workers studying dispersion of T. infestans between infested houses.

Interference with reproduction in Glossina morsitans morsitans Westw. by diflubenzuron depends on a variety of factors that influence its uptake and loss from the female fly. The duration of its eftect depends on the site and method of application to the fly as well as the amount of material applied. In nulliparous females, loss of diflubenzuron was by excretion, but as the fly aged approximately 50% of the material remaining within the fly was lost with each larviposition. Following injection, the rate of loss of diflubenzuron by excretion was twice that from flies treated topically, but in neither was it directly related to the amount of diflubenzuron within the fly. Loss to the in utero larva, however, was governed by the amount of material within the fly, at least 9 ng diflubenzuron being necessary for production of an abnormal offspring. In injected flies, the overall loss was twice that from flies treated topically on the dorsal thorax and similar to those treated topically on the ventral abdomen. This difference in the rate of loss from topically-treated flies seems to be related to the amount of material available on the surface of the fly, the cuticle apparently acting as a storage site from which there is a gradual release of diflubenzuron into the fly.

Liothrips mikaniae (Priesn.) comb. n. is one of the most promising biological control agents for Mikania micrantha, a sprawling composite vine native to the Neotropics which is a serious weed of plantations in South-East Asia. A description and illustrations of the adult and larvae of this thrips is followed by details of the life-history, culture technique, host specificity (including laboratory studies demonstrating oligophagy) and natural enemies. It is recommended for introduction to South-East Asia.