Several published reports have presented estimates of the rate of increase, r, based on sampled ovarian age distributions from Glossina populations throughout Africa. These estimates are invalid, because an age distribution sampled at one point in time can be equated to a survivorship curve only if r = 0. When such a survivorship curve and a corresponding fecundity schedule are then used to estimate r via the Euler-Lotka equation, the result is a value of r near zero, regardless of the population's true rate of increase. Synthetic sampling from a hypothetical tsetse population confirmed that estimates computed in this fashion are entirely the products of sampling error. Valid estimates of r can sometimes be obtained from an age distribution, using an alternative method, but such estimates are highly sensitive to sampling errors in the distribution.

Tamarixia leucaenae sp. n. is described from Trinidad as a parasitoid of Heteropsylla cubana Crawford. The psyllid is a serious pest of Leucaena leucocephala, which is used as a shade tree in plantations of various crops in the tropics.

Rastrococcus invadens Williams, a pest of fruit and ornamental trees in West Africa, was introduced from the Oriental Region. In 1986, a search was initiated in India for natural enemies of Rastrococcus spp. with a view to selecting potential biocontrol agents for introduction into West Africa. The results of the survey, laboratory breeding of the hosts and their natural enemies and host-specificity of the natural enemies are reported. Based on host-acceptance tests, two encyrtids, Gyranusoidea tebygi Noyes and Anagyrus sp., have been sent to UK for further screening.

Major potential sources of variation in the feeding of Nilaparvata lugens (Stål) which are not host-dependant are those related to time, i.e. the age of the insect, the length of time the insect is in association with the plant and the time of day. These parameters were investigated with a susceptible, a moderately resistant and a resistant rice variety using honeydew clocks for the collection of honeydew excretion data. It is concluded that there are non-circadian patterns of honeydew excretion which are related to the degree of resistance of the variety and that such feeding and excretion patterns can be used to characterize the relationship between insect populations and rice varieties.

An immunoassay for the carboxylesterase E4, which confers insecticide resistance in Myzus persicae (Sulzer), was used to monitor the distributions of E4 activity within samples comprising more than 5000 aphids from sites in eastern and southern England. The quantitative precision of this assay is an improvement on the subjective assessment of E4 band intensity on electrophoresis gels previously used. Activity distributions did not always show discrete components corresponding to S, R1, R2 or R3 variants and thus, though convenient, this classification should be used cautiously. Distributions derived by immunoassay of many insects from the field are best compared to those of laboratory-reared standards classified according to E4 quantity (V1-V64). Data from untreated crops are presented in this way and discussed in the light of previous surveys. A large proportion of aphids corresponding to the V8 variant (intermediate between ‘R1’ and ‘R2’ categories) were found, and frequencies of resistance differed on both a local and regional scale. The majority of aphids from treated crops had E4 activities equivalent to, or above, that of V16 (i.e. ‘R2’).

Rhopalosiphum maidis (Fitch) collected on barley in the northern hemisphere usually has a ten-chromosome karyotype, whereas samples from maize, sorghum and Johnson grass (Sorghum halepense) from all parts of the world commonly have 2n = 8. Samples with other karyotypes (2n = 9, 2n = 11 and 2n = 8 heterozygous for an interchange between the X chromosomes) occur less frequently on these and other species of Gramineae. Multivariate morphometric analysis, principally by the method of canonical variates, indicated that the ten-chromosome form may be regarded as a single clone of R. maidis recognizable by its karyotype and host-plant relationships, although not completely separable by morphology alone from all other clones of this permanently parthenogenetic species complex.

Rastrococcus invadens Williams, a serious pest of fruit crops in West Africa was studied under controlled conditions. The different stages of the mealybug are described and data given on development times, adult lifespan, fecundity, sex ratio and mortality rates. Similar data are also given for a primary parasitoid, Gyranusoidea tebygi Noyes. The parasitoid completed almost two generations for each one of the mealybug and had a female-biased sex ratio compared with a male-biased one for R. invadens. The parasitoid did not parasitize other species of mealybugs offered. G. tebygi was considered a suitable candidate for a biological control programme and was introduced into Togo in October 1987.

The frequency of DDT resistance in Anopheles culicifacies Giles in Sri Lanka remained relatively constant from the cessation of DDT use for malaria control in 1975 until 1982. From 1983 to 1986, the frequency of resistance decreased slowly but significantly. In contrast, the resistance gene frequency in A. subpictus Grassi declined between 1980 and 1983, after which the trend was reversed, and there was a significant increase in DDT resistance in 1984–86. This rise in DDT resistance cannot be attributed to positive DDT selection pressure as there has been little or no agricultural use of DDT during this period. It is also unlikely that the rise in resistance is due to pyrethroid selection as the quantity of pyrethroids used on the island is low and there is no evidence of pyrethroid resistance from WHO susceptibility tests. Studies with the synergists FDMC (4-chloro-α-(4-chlorophenyl)-α-(trifluoromethyl)benzenemethanol) and piperonyl butoxide indicated the involvement of DDT-dehydrochlorinase rather than oxidase in the resistance. This was confirmed by metabolism studies, as DDT-resistant adults of both A. culicifacies and A. subpictus showed an increase in the rate of DDE production, which was also correlated with an increase in glutathione transferase activity.