Two mark-release-recapture experiments were carried out on a female population of A. africanus in the Zika Forest, in Uganda, to estimate density, survival rates, dispersal range and duration of the gonotrophic cycle. Marking was achieved using powdered fluorescent pigments and wet paint. In the first experiment, unfed A. africanus female mosquitoes were marked and released. A high overall recapture rate of 17.6% was recorded consisting mainly of first recaptures (up to 85.6%). The highest recapture rate was recorded during the first 4 days after release. Using Jolly's Stochastic Model, daily population estimates ranged from 1386 to 8406 during the first 7 days of release. The daily average population estimated over the first 10 days was 3591. Using the Simple Lincoln Index, population estimates ranged from 1104 mosquitoes to 16,320 with an average daily estimate of 3706. Of interest was the fact that the average daily population estimates using the two methods were not statistically significant. The 24-hr survival rate averaged over 9 days was 0.9228. Dispersal was rather random, and appeared to be of a limited range with an average distance of 50 m. In the second experiment, which involved marking only fully engorged mosquitoes, an overall recapture rate of 7.1% was recorded, with an average daily survival rate of 0.8209 averaged over the first 4 days. The pattern of recaptures indicated a gonotrophic cycle of 5–6 days with a small proportion of mosquitoes seeking secondary feeds during the first 48 hr. It was generally observed that marking and handling did not have any marked effect on mosquitoes during the first 8 days.

Orseolia oryzae, the rice gall midge, is a major pest of rice in many areas of tropical Asia and is becoming an important pest in Africa. A chronological review of the progress made in various national programmes on varietal resistance, sources of resistance and breeding for resistance is given. Many resistant varieties have been identified and have been utilized in breeding programmes to develop high yielding varieties with multiple resistance to the gall midge and other insect pests and diseases. Mechanisms and inheritance of resistance in rice varieties are discussed. Rice varieties resistant in various countries and sources of resistance used in breeding programmes are listed. Biotype variations in different countries and within the countries are revealed, and a preliminary classification of gall midge biotypes based on varietal reactions is proposed.

Occurrences of outbreaks of the African armyworm, Spodoptera exempta, between January and December for 19 years (1961–1979), and records on nightly moth catches from light trap stations located between southern Kenya and east-central Tanzania (1–8°S and 35–41°E) for 16 years (1963–1978), have been mapped, tabulated, and analysed on a standard weekly time-table, in order to compare events occurring between the ‘off-season’ months of July to November and the beginning of the ‘outbreak seasons’ from December or January. Circumstantial evidence from the above, coupled with analysis of climatological statistics for rainfall, temperature and windflow over the area and period, support the hypothesis that populations of S. exempta can survive between southern Kenya and eastcentral Tanzania during the off-season months, and contribute to the initial development of ‘outbreak seasons’ in Tanzania or Kenya. Methods for monitoring and analysing such developments for improving the efficiency of the Armyworm Forecasting Service in East Africa are suggested.

The susceptibility of third-instar Spodoptera exempta (Walk.) to a heat-treated nuclear polyhedrosis virus was tested in the laboratory. The polyhedral suspension was purified by differential centrifugation and heat-treated at temperatures that ranged from 20 to 90°C for 10–30 min. The LT50 ranged from 108.4 hr for virus heated at 50°C (10 min) to 162.2 hr for virus heated at 80°C (10 min). The fiducial limits to the LD50s were calculated at 0.95 probability.

An intensive sampling programme for the estimation of the absolute size of the population of the cattle pest Stomoxys nigra Macquart in the sugarcane agro-ecosystem is proposed. Attention is focused on: (a) sampling at field level; and (b) sampling at national level. The best way of allocating the limited sampling resources between the various sub-divisions of the habitat to achieve efficient estimation is considered.

This paper is an attempt to synthesize information available on C. p. quinquefasciatus in Africa. The latter is presently found in most urban areas of the African continent and in rural settlements which show some trends towards urbanization. In East Africa, and the islands of the Indian Ocean, C. p. quinquefasciatus is one of the major natural vectors of Wuchereria bancrofti. In addition it can also transmit, under laboratory conditions, some other pathogenic agents.

Preimaginal forms develop in different kinds of man-made breeding-places, especially those containing polluted water. The situation in each African region is reviewed in detail.

Female behaviour during the different phases of the gonotrophic cycle is analysed, together with population dynamics.

Control methods by synthetic insecticides are discussed in relation to resistance problems and the characteristics of the breeding sites. Other control methods based on the use of growth regulators, genetic manipulation, biological agents (parasites and predators) and environmental management have been investigated as well. Most of them cannot be easily applied or are not yet applicable for control operations.

The numbers of the separate cohorts of the cocoa shield bug Bathycoelia thalassina which were observed up to hand-height on 50 cocoa trees in a Nigerian cocoa farm were recorded. The data were analysed for any patterns of aggregation. In the egg as well as 1st to 3rd nymphal instar stages, B. thalassina was highly aggregated on individual cocoa trees and the coefficients of aggregation ranged from 2.14 to 2.77. In the 4th and 5th nymphal instar and the adult stages distribution was random and analyses of data in units of 1, 2, 4, 8 and 16 cocoa trees did not reveal any patterns of aggregation.

More egg batches were laid on stem than on pods and the least number of batches was found on the leaves. There was no significant difference in the size of batches laid on different plant parts (P < 0.05) and cocoa pods did not influence the choice of oviposition sites by B. thalassina.

The implication of this distribution pattern was discussed, and a suggestion made for spot application of insecticides on the eggs or 1st instar nymphs as a method of control that would be both economical and of ecological advantage.

A method of marking tsetse flies is described based on the transfer of fluorescent pigment from marked males to females during copulation. Powder applied between the coxae of the male lodges in the scutellar groove of the female during mating. Powder persists well on males before mating and on females afterwards. Individual males can mark several females, and the marks of different males can be detected on females after multiple mating. Aspects of behaviour which may possibly be investigated using this method are described.

Diapause in the pink bollworm, Pectinophora gossypiella, is a quantitative genetic character that is in turn regulated by external environmental factors. A naturally occurring non-diapause strain of the insect from south India and two diapause strains from Arizona (U.S.A.) were used in crosses to study the inheritance of diapause. The F progeny expressed a diapause response intermediate between the two parents and no clear dominance was evident for the non-diapause character. It was not possible to classify the phenotypes of backcross and F2 progeny in accordance with simple Mendelian ratios. Comparisons of reciprocal crosses indicated that the progeny from male parents of the Indian strain usually had a lesser incidence of diapause. Such sex related differences were more evident in F2 progeny and backcrosses. It is therefore concluded that diapause in the pink bollworm is inherited in a complex way and that non-diapause is not completely dominant over the diapause trait. The study also indicated that incomplete dominance for non-diapause involves a sex-linked gene.

The head capsule widths of larvae of the cowpea pod-borer Maruca testulalis, reared individually and crowded together in the laboratory were measured. The measurements were subjected to a test of analysis of variance, frequency distribution and Dyar's rule. All methods gave a total of five larval instars in the life cycle and conformed to Dyar's rule. There was a high positive correlation (r = 0.97) between the size of the head capsule and the period of development elapsing. The minimum duration of larval development was 9 days.

A two-choice type bioassay has been used to screen extracts from a number of plants of the sagebrush community for their antifeeding properties against the Colorado potato beetle, Leptinotarsa decemlineata Say. The extracts of Artemisia tridentata, Purshia tridentata and Chrysothamnus nauseosus have been fractionated for their antifeeding constituents. Known constituents of these plants (deacetalmatricarin, coumarins, cucurbitacins, polyphenols, polyacetylenes, and essential oils) were also screened. The results indicate that several chemical classes of compounds are responsible for antifeeding activity in each plant. Water soluble substances present in the waste marc after steam distillation of peppermint oil were highly active, too.

Changes in the physiological status of the host rice plant had a profound effect on wing morphism in the brown planthopper, Nilaparvata lugens (Stål). Significant increases in macroptery in the hopper progenies reared on senescent or hopperburned hosts occurred mainly because of a general decline in the host's nutritional status and allelochemic factors. Starvation of young nymphs on nutritionally-depleted hosts probably inhibits the secretion of juvenile hormone by the corpus allatum, suppressing brachyptery and expressing macroptery. Also, any juvenilizing effect of the host's allelochemics would tend to dissipate with the host's senescence. Therefore, the proportion of macroptery in the hopper progeny developing on the rice host plant is determined by the extent of depletion of the host's nutritional allelochemic factors. The observed significant increase in macroptery at a density of 50 or more hoppers per plant may have also been mediated through the host plant. Brown planthopper progenies of macropterous and brachypterous Biotypes 1, 2, 3 and the field population differed in their expression of macroptery probably because of their inherent differences in sensitivity to macropteryinducing stresses.

During sporadic outbreaks of S. exempta, population densities sometimes reach extremely high numbers. Monitoring at one such outbreak revealed that a considerable synchrony exists in the developmental processes of such populations, so that at times up to 97% of the population is represented by only one stage of development. Heavy pupal mortality with symptoms of a cytoplasmic virus infection was noted. Flight behaviour of emerging adults revealed observable differences in the flight activity of the moths. Although a great majority of the emerging moths flew away from the area, some stayed back. Eggs layed by the latter produced a second brood but, due to a more or less total depletion of the food source, this subsequent brood did not survive in any appreciable numbers and finally died out.

Assessments were made of the applicability of various methods of monitoring tsetse populations for control projects in Niger and Mozambique. Biconical traps proved most effective for sampling G. tachinoides in riparian habitats of Niger, and vehicle patrols for G. morsitans morsitans in savannah woodland of Mozambique. Comparisons are drawn between the various methods in terms of species, sex and physiological composition of catch, patterns of diel activity, and detection of fly concentrations.

In West and Central Africa attention has recently been drawn to the role of commercial crop plantations in the creation of new tsetse habitat, and the problems this poses to trypanosomiasis control. Reported here is the colonization by the tsetse, Glossina pallidipes Austen, of a plantation of a very different kind—exotic coniferous forest. This has been observed in two localities in Kenya: the Lambwe Valley in the west, and the Shimba Hills near the coast. The features of this habitat, and the factors associated with its exploitation by tsetse, are described, with particular reference to the Lambwe Valley situation. While extension of tsetse fly-belts by afforestation practise is unlikely to be a problem of widespread significance in Kenya, afforestation policy ought, in particular circumstances, to take into account the tsetse and trypanosomiasis situation, the Lambwe Valley being a case in point.

Non-setting adhesives available were assessed for catching insects of medical and veterinary importance. Physical, chemical and handling properties are described. The results of tests are given using the most suitable adhesives against Glossina spp. (tsetse), Aedes aegypti (mosquito), Lutzomyia longipalpis (sandfly), triatomid bugs and cockroaches. Details are given of a formulation suitable for the capture of most insects in a variety of climatic conditions. The manufacturer's addresses are given to prevent difficulties in ordering and obtaining these products.

The onset of oviposition, incubation period, instar duration and polymorphism in the first progeny of Macrotermes michaeheni were investigated. Most incipient colonies have their first batch of eggs within the first week following establishment of the colonies. The incubation period for these eggs was 36.2 days. Three male and female larval instars, minor and major workers, and minor soldiers were found in the first progeny. Neither fourth instar larvae, which subsequently moult into major soldiers, nor nymphs, which develop into reproductives, were detected.

The duration of each larval instar was determined. The longest duration was that of third instar larvae developing into both minor and major workers. The first neuter terminal castes which appeared in the colonies were minor workers, followed by major workers and, soon after, by minor soldiers in the majority of cases.

Glossina tachinoides and G. morsitans submorsitans in Niger and G. morsitans morsitans in Mozambique conform to the general pattern of Glossina resting behaviour in that they rest on the woody parts of the vegetation during the day and on the foliage at night. G. m. submorsitans and G. m. morsitans both prefer low horizontal branches as their main day-resting sites, while G. tachinoides rests mainly on the bases of trunks. G. m. morsitans was found to exhibit a 3-phase pattern of resting behaviour: on foliage at night; low down on trunks for a short period after dawn; and on branches higher up for the remainder of the day. No relationship between temperature or relative humidity on the choice and vertical distribution of night resting sites could be found. For G. tachinoides, the microclimatic conditions of its resting sites were more favourable than ambient conditions during the middle of the day.