Genetic variation of resistance and tolerance to stem-borer, Chilo partellus, was studied in three sorghum crosses. Parents, F1 and F2 progenies were evaluated for per cent foliar damage and stem tunnelling as a measure of resistance or susceptibility. The parental cultivars involved in the crosses represented a fairly distinct range of character expression for plant height, foliar damage, stem tunnelling, stem lodging and grain yield. Means, degrees of dominance in F1 and inbreeding depression in F2 suggested that susceptibility was dominant over resistance in crosses susceptible x resistant and susceptible × tolerant, while resistance was dominant over susceptibility in the cross tolerant × resistant. The variation patterns of foliar damage and stem tunnelling in parents, F1 and F2 progenies suggested that they are different and are independently inherited. Both resistance and tolerance mechanisms are operating in sorghum resistance to stem-borers and these mechanisms are independently inherited. Estimates of heritability (broad-sense), genetic coefficient of variation and expected genetic advance, indicated that the cross Serena (tolerant) x IS 2146 (resistant) provides maximum chances of selecting resistant and tolerant plants in the segregating populations. Recurrent selection (population breeding) is suggested to improve the level of stem-borer resistance and tolerance and yield in sorghum.

Loss estimates for wheat insects in Africa and Asia have not received adequate attention. However, in PDR of Yemen, pests including insects, diseases, weeds and birds can cause 10™70% loss of wheat crop. Aphids are considered to be the major insect pests of wheat in the country. A survey of indigenous natural enemies has shown that they may contribute to overall aphid control. Sowing date experiments have shown that sowing in November led to higher yields and lower insect infestation than sowing in October and December. The insecticides tested achieved a significant control of aphids and higher yields when compared with unsprayed plots. A single application of malathion or dimethoate before mid-January was recommended for chemical control.

The behavioural responses of Adisura larvae to different concentrations of the Lablab niger plant extract was tested under laboratory conditions. The concentrated plant extract did not elicit positive response from Adisura larvae. The first instar Adisura larvae preferred 10% concentration of the extract over higher concentrations (i.e. > 10%). First instar Adisura larvae were found more sensitive in discriminating non-host from the host than last instar larvae. Adisura gravid females laid no eggs on blackgram, cowpea, broadbean, redgram and PLS-24, a field bean (L. niger) variety. This study suggests that redgram, cowpea, broadbean, blackgram and soybean are not the primary hosts of A. atkinsoni.

Pigeon pea (Cajanus cajan L. Millsp.) and cowpea (Vigna unguiculata L. Walp) are the major grain legumes grown in the semi-arid areas of Kenya. Heavy losses in grain yield occur due to their vulnerability to a large number of insect pests in the field as well as damage by weevil during storage. Aphids, thrips, pod-borers and pod-sucking bugs are common insect pests to both pigeon pea and cowpea. Pod fly mostly attacks pigeon pea, and apion beetle is a serious pest of cowpea. Use of chemical control in the semi-arid areas is expensive and beyond the reach of the small-scale farmers. Work on development of less susceptible or tolerant crop varieties has been initiated at the National Dryland Farming Research Station (NDFRS) at Katumani. Results of preliminary screening against major insect pests are reported in this paper.

The sources of resistance against aphids and thrips in cowpea, were received from the International Institute of Tropical Agriculture (UTA), Nigeria, and information on their reaction to these insects under field conditions has been discussed. In pigeon pea, resistance against pod-sucking bug, which appear to be of the antibiosis type, has been identified in the early maturing group of the local germplasm. Implications of breeding for insect resistance and pest management in the two crops are discussed.

The relative resistance of rice varieties to Maliarpha separatella was studied during 1981 and 1982 long rain seasons. The observations covered the laying of egg masses, tiller infestation, incidence of “whiteheads” and, in some cases, the grain yield.

The results indicated that the varieties BG 34™8 and BG 90™2 received the highest egg masses per plot which apparently caused “whiteheads”. The remaining 10 varieties only indicated moderate response. The 1982 long rain season under no control and carbofuran 5G application regimes showed reduced tiller infestation only in BG 90™2 and Basmati 217. The five tested varieties did not show any marked difference in tiller infestation under the two regimes. Hence, BG 90™2 and Basmati 217 showed some susceptibility of M. separatella, while the rest of the varieties remained moderately resistant.

Moth population varied according to the growth stages of the rice crop in the field, with the peak occurring during the booting to maturation stages.

Observations of the diurnal resting behaviour of Glossina longipalpis and Glossina fusca congolensis were carried out at Ele forest, Oke-Ako between September 1975 and May 1976 both inclusive. The two species of tsetse were observed resting most frequently on underside of stems and branches with diameter range 1–60 mm. Some G. fusca congolensis rested vertically. Whether resting vertically or obliquely, this species always rested with head pointing downwards. More than 95% of G. longipalpis and G. fusca congolensis rested between the heights of 20–240 cm. Preferred resting objects included shrubs, young saplings, climbers and, during high temperatures, bases of tree trunks.

For control purposes it is suggested from the above information that a discriminative and selective spraying of the area be planned for the late dry season and early rains when fly populations are more concentrated and individual flies tend to rest at lower heights. The spraying which should be directed to the undersurface of resting objects will help to reduce the risk of trypanosomiasis at the Oke-Ako cattle ranch.

The information available on the genetics, breeding, and utilization of host plant resistance to 14 of the most important species of maize stem-borers complex, their biology, and the damage done to the crop is presented.

The components necessary for implementing a programme for breeding for resistance to stem-borers in maize include: a colony of the pest(s), the capability to mass rear them, uniform artificial infestation methods, an array of the available maize germplasm or related species, rating scales and evaluation methods that permit identification of genetic resistance, knowledge of screening and breeding methods, and the personnel and resources to execute the programme.

The paper having emphasized the importance of each component, concludes with a discussion of several HPR programmes and the breeding methods being used in various areas of the world, to develop and utilize resistance to one or more maize pests, as a proven method for gaining increased management control over these pests.

Losses of stored seed to insects in the tropics have reached levels of major concern. Synthetic insecticides, while effective, are generally very expensive for small fanners. The efficacy of two plants, Hyptis spicigera and Cassia nigricans, used by farmers to control insect infestation in stored cowpeas was determined. The oviposition and hatching of bean weevils (Acanthoscelides obtectus), under controlled environmental conditions, were reduced following treatment with EtOH extracts (1 g plant material 1 ml EtOH) at low application rates with EC50 between 0.3 and 14 μl extract/g bean. Further field studies are proposed to determine if such natural products can be further exploited to reduce stored legume losses.

A large pond, up to 2000 m2 area, adjacent to the sea at Jimbo, near Vanga, on the south coast of Kenya was studied for salinity and the presence of mosquito larvae 1980–1981. Rainfall peaked in November–December 1980 and again in March–May 1981, while salinity of the pond-water fluctuated inversely from dryness in February, more than 100% seawater equivalent in months before main rains, to below 13% seawater after the onset of rain in March.

Five types of mosquito larvae occurred in the pond: Aedes albocephalus mostly at 21–30% salinity (range 13–30%); Culex sitiens mostly at 31–40% salinity (range 13–54%); Culex tritaeniorhynchus and Culex thalassius mostly at 41–50% salinity (range 13–50%) and the Anopheles gambiae complex from 13 to 54% salinity, at least those at higher salinities being Anopheles merus. No larvae were present when salinity surpassed 54% through evaporation, or fell below 13% after rain. The most reliable way to limit or control these pest and vector mosquitoes at Jimbo would be to drain the pond into the sea after rainfall, so that mosquito populations could not increase by breeding sequentially, while salination proceeds.

The American bollworm, Heliothis armigera Hüb. is the major cotton pest in Tanzania. The commercial cotton varieties have the ability to compensate for early loss of fruiting points caused either by physiological stress or by bollworm damage; and therefore early sowing, together with a blanket spraying regime, is recommended to minimize the damage caused by this bollworm. To extend this integrated approach, studies to incorporate Heliothis -resistant characters, viz. frego bract, nectariless, high gossypol and glandless into the Ukiriguru cotton varities, were started in the early 1970s and are still in progress. To date, frego bract has given consistently good results; and intensive work is under way.

The induction of resistance in the urban pest mosquito, Culex quinquefasciatus, to chlorpyrifos and chlorfenvinphos and the cross-resistance spectra of these selected lines to propoxur and a number of organophosphate insecticides was studied. Distinct genetic factors governing intermediate (R1) and high (R2) levels of larval resistance to organophosphates were found to be allelic according to the single locus, multiple aliele hypothesis. Adults were less susceptible to malathion and fenitrothion after larval selection with chlorpyrifos, but the degree of resistance was found to be much less than that in the larvae. The implications of these results for the control of C. quinquefasciatus in Dar-es-Salaam, Tanzania, is discussed.