Comparative field studies were conducted during the rainy and dry seasons at the Mbita Point Field Station of ICIPE in southwestern Kenya, to investigate the pattern and rate of dispersal of Aphis craccivora on aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cowpea cultivars in relation to key weather factors. The effects of the dispersal trends on crop performance and aphid population dynamics were analysed. Treatments consisted of initial aphid releases at the north, south, west, east and centre of test plots and uninfested controls maintained on plants for 22 days. Parameters recorded included: pattern (direction of spread of aphids) and rate (number of aphid-infested plants at a given time) in test plots; crop growth and yields and associated factors such as incidence of sooty mould and plant mortality, and aphid density and associated factors, including the incidence of natural enemy species, particularly coccinellids. Dispersal was fastest when releases were made in the west, north and centre of plots, and resulted in adveVse effects on ICV-1 growth and yields. Infestations of ICV-12 did not significantly affect crop performance. There was an apparent direct, positive relationship between wind direction and pattern of spread of aphid infestations, but this pattern was more apparent during the rainy season, when wind speeds were higher, than during the dry season. The incidence of natural enemy species correlated with the spread of aphid infestations, while the abundance of coccinellids correlated with aphid density.

Aphis gossypii is one of the major pests of cucumber grown in greenhouses in the coastal areas of Morocco. A population dynamics study showed that A. gossypii populations might reach very high levels in June, causing economic damage to cucumber. The proliferation of A. gossypii on cucumber arises mainly from infestations by flying winged adults. Factors regulating the fluctuation of population of the species are discussed.

The host plant spectrum of Aphis gossypii Glover (Hemiptera:Aphididae) was assessed from 1991 to 1994 in the cotton-growing zone of northern Cameroon. The aphid is generally present on cotton (Gossypium hirsutum L.) and okra (Abelmoschus esculentus (L.) Moench) during the rainy season. During the dry season on the other hand, A. gossypii is observed on a very wide range of plants (63 families, 192 genera and 302 species). During this season, all types of plants, especially legumes, dry-season crops and various types of trees, are colonised. From the representativeness of the sampled plant species within the cotton zone of Cameroon, it is concluded that a part of the A. gossypii population survives the dry season in the Sudano-Sahelian African zone, thus forming numerous reservoirs scattered among plants and in very varied habitats.

The termite species Psammotermes hybosloma Desneux and Anacanthotermes vagans (Hagen) foraging in the desert ecosystem of Kuwait preferred to consume dried leaves of Tamarix aphylla (L.) and Rhanterium epapposium Oliv. over the other plant species tested. This preference varied with season. The termites consumed more food during summer than winter, with the highest consumption being recorded in September, the time of the year when the food plants dry up and can be readily cut into fragments which are carried by workers to the underground nest. These results indicate that the contribution of termites to the removal of desert vegetation is less than that of other soil fauna.

Termite damage to annual crops on smallscale farms was surveyed in eight areas in southern Malawi during 1989/90 to 1991/92. The most frequently grown crop was maize, followed by pigeonpeas, Phaseolus beans, cotton, cowpea and groundnuts. Twenty-seven species of termites were found attacking crops. The most numerous and widely distributed were several species of the Macrotermitinae, including Ancistrotermes latinotus, four species of Macrotermes, four species of Microtermes, three species of Odontotermes and Pseudacanthotermes militaris. All species damaged maize but only a few damaged bambara, cassava and banana. The damage appeared to be more frequent in dry areas than in wet ones.

A survey for laccase, an enzyme involved in phenol oxidation, was carried out in 23 termite species from three different feeding guilds. In soil-feeding (6 species) and wood-feeding (7 species) termites, laccase activity was not detected. In contrast, all the fungus-growing termites (10 species) tested showed laccase activity. The symbiotic fungi (conidia) and fungus combs showed higher activity than the termites themselves in 6 species: Macrotermes bellicosiis, M. miilleri, Odontotermes sp., O. sp. aff. interveniens, Pseudacanthotermes spiniger and P. militaris. Fungus combs always had the highest laccase activity. The absence of laccase activity in soil-feeding and wood-feeding termites is discussed. The presence of laccase activity in both termites and Termitomyces constitutes novel information relevant to the degradation of phenols.

In this study, Coccinella septenipnnctata was efficient in controlling Aphis gossypii populations on cucumber in the greenhouse. This efficiency was a function of the predator/prey ratio and the initial aphid density at the time of release of the predator. Prey density had a large influence on the fecundity and establishment of this coccinellid in the greenhouse.

Field experiments were carried out at Coimbatore, Tamil Nadu State, India, for four consecutive years (1990–94), to monitor the seasonal activity of Cotesia flavipes Cameron (Hymenoptera: Braconidae), a larval parasitoid of gramineous borers, including the sugarcane shoot borer (Chilo infuscatellus Snellen), sugarcane internode borer (Chilo sacchariphagus indiens (Kapur) and sorghum stemborer (Chilo partellus Swinhoe) (all Lepidoptera: Crambidae). The highest levels of parasitism (0.0–17.9%) were recorded on Ch. partellus followed by Ch. sacchariphagus indiens (0.0–8.3%) and Ch. infuscatelliis (0.0–1.1%). The parasitoid was collected in Ch. partellus and Ch. sacchariphagus indiens in all the four study years, whereas it was not observed in Ch. infuscatelliis during 1993–94. Parasitism rates in Ch. partellus were positively correlated with minimum temperature and afternoon RH. In Ch. sacchariphagus indiens, parasitism levels showed significant negative correlation with minimum temperature. Parasitism rates in Ch. saccharipliagus indidus larvae collected during harvest from seven sugar factory areas of Tamil Nadu State were lower in 1992–93 (0.0–1.8%) and higher in 1993–94 (0.0–3.2%) than those recorded at Coimbatore in the corresponding period (December-March). Cotesia flavipes was the only larval parasitoid recorded from the borers both at Coimbatore and the seven sugar factory areas surveyed in Tamil Nadu.

A tsetse-control trial was carried out in a primary forest habitat on Unguja Island of Zanzibar to assess the effect of insecticide-impregnated blue cotton screens on a population of Glossina austeni Newstead. In November 1991, screens were deployed at densities of 45–70 per km2 and the fly population was monitored monthly using sticky panels. Both female and male daily catches were not affected during the initial five months after screen deployment, but the physiological age distribution of female flies shifted significantly towards younger groups. Females were more influenced by the screens than males. The fly population was very low after the long rainy season, but increased to pre-control levels three months after the flooding of the forest floor. Thereafter, male and female apparent densities decreased, and 78–91% and 98–99% suppression was obtained for males and females respectively at the end of the 18-month intervention period. While effective control of G. austeni using blue cotton screens was shown to be feasible, it required a high deployment density and a long intervention period.

Experiments on the effects of KK-42, an anti-juvenile hormone imidazole derivative, on the rearing and reproduction of Bombyx mori L. were carried out in a hot, wet summer in West Bengal, India. A single dose of 3 μg KK-42/larva induced precocious metamorphosis in a bivoltine hybrid (KPGB × P5) race of B. mori when applied topically to freshly moulted (less than 1-h old) fourth instars, and increased their rearing performance over control tetramoulters. However, cocoon and shell weights, shell ratio and filament length were reduced by the anti-JH treatment. Final body weight and head capsule width of the treated fourth instars were significantly higher than those of the controls. Bivoltine trimoulter males also showed good capacity for mating with multivoltine Nistari females. The possibility of obtaining three-way multi-bi hybrid eggs during the wet part of summer in a tropical climate is discussed.

The aim of the present study was to determine, by a field experiment, whether the seasonal variations in the levels of cyanide and rutin in the phloem, secondary compounds potentially implicated in cassava resistance to the cassava mealybug (Phenaccocus manihoti), could be influenced by different kinds of soil fertilisation (manure, NPK, KC1, lime, mulch). It was found that mean cyanide and rutin contents varied significantly with season, soil treatments and infestation. For each soil treatment, the highest contents of these compounds on uninfested plants was registered in the main dry season (Jul-Aug) for cyanide and at the end of the dry season (Jul-Aug) and beginning of the rainy season (Oct-Nov) for rutin. The infestation factor induced an increase in cyanide and rutin contents for 43 combinations of period and soil treatment among 48 in total. For cyanide content (phagostimulant function in mealybug), this increase appeared significant at the end of the rainy season (Apr-May) and in the main dry season (Jul-Aug) for control and KC1 fertilisation. For rutin content (an unfavourable substance for the insect) significant increase was induced by infestation in each period for manure and mulch and especially in the main dry season (Jul-Aug) and at the beginning of the rainy season (Oct-Nov) for other soil treatments. Concerning the seasonal variations in the level of rutin, these results showed that mulch and manure are the best fertilisers to increase cassava resistance against mealybugs.