Southern Sudan has tremendous agricultural potential, particularly in the high rainfall green belt of western Equatoria that borders the Democratic Republic of the Congo. A wide range of tropical and semi-tropical crops is grown there in a variety of complex cropping systems. Although a long civil war severely disrupted agriculture in the region, there is now hope that the recent peace accord will return stability and agriculture will remain a mainstay of a revived economy in western Equatoria. The environment supports crop production, but pests and diseases also thrive, although very little has been recorded about them. This article represents the sole record of an agricultural insect pest collection and disease notes assembled at Yei over several years in the early 1980s, but which were destroyed during the civil war. It is hoped that these notes will be useful in addressing biotic constraints to rehabilitation of agriculture in western Equatoria. Traditional methods of pest and disease management will be particularly important given the poor state of the economy, the need to produce crops for subsistence farming and the relative geographical isolation and poor communications that characterize southern Sudan. Le sud du Soudan offre d'énormes potentialités de développement agricole, en particulier dans la ceinture verte humide de la région Ouest de l'Equateur qui borde la République Démocratique du Congo. Une large gamme de cultures tropicales et subtropicales y est cultivée selon une grande variété de systèmes culturaux complexes. Bien qu'une longue guerre civile ait sévèrement perturbé l'agriculture de la région, il y a maintenant un espoir que les accords de paix récemment signés rétablissent la stabilité et que l'agriculture puisse constituer la base d'un renouveau économique dans l'Ouest de l'Equateur. L'environnement est favorable á la production agricole, mais également au développement des ravageurs et des maladies, bien que nous ayons très peu d'informations. Cet article constitue une source unique d'informations sur les insectes ravageurs et les maladies des cultures répertoriées pendant plusieurs années au début des années 80 dans la région de Yei, mais dont les notes ont été détruites pendant la guerre civile. On espère que ces notes seront utiles pour identifier les contraintes biotiques et permettre la réhabilitation de l'agriculture dans l'Ouest de l'Equateur. Les méthodes traditionnelles de gestion des ravageurs et des maladies seront particulièrement importantes compte tenu du mauvais état de l'économie, du besoin de produire des cultures de subsistance, du relatif isolement géographique et des mauvaises communications qui caractérisent le sud du Soudan.

The sweet potato whitefly Bemisia tabaci (Gennadius) is a pest of diverse agricultural systems worldwide, owing to its capacity to transmit viruses, both intraspecific and host-associated variations. In Ghana, it is the only known arthropod vector for cassava-infecting begomoviruses (Geminiviridae). Two genetic variants of B. tabaci, previously characterized by RAPD–PCR and subsequently reared on cassava and okra, were allowed access to five weed species in order to examine host preference and suitability: Amaranthus retroflexus, Chromolaena odorata, Desmodium tortuosum, Euphorbia heterophylla and Malvastrum coromandelianum. Overall, the duration of the life cycle ranged between 16.5 and 26.3 days and survival rates were 0–27.5%. The population from field-infested okra reproduced and developed to maturity on C. odorata, D. tortuosum and E. heterophylla. Both populations produced male and female progeny. Amaranthus retroflexus and M. coromandelianum were considered poor hosts for both populations, due to the low fecundity and survival of eggs, pupae and adults. The rearing host did not significantly (P>0.05) influence survival on subsequent hosts in either case. The host-restriction of the population collected from cassava was not corroborated here, based on the demonstrated ability of the Ghanaian cassava population to complete its life cycle on D. tortuosum and E. heterophylla. It was estimated that B. tabaci could achieve 13–22 generations per year in Ghana. Removal of C. odorata, D. tortuosum and E. heterophylla from the vicinity of susceptible crops is recommended.

The parasitic wasp Anisopteromalus calandrae (Howard) was released at six (5, 10, 20, 30, 40 and 50 pairs) densities to evaluate the effects of different introduction rates in controlling residual populations of the lesser grain borer Rhyzopertha dominica (Fabricius) in wheat grain stored in bulk in 46 m2 rooms. At the 50-pair density, the parasitoid suppressed 83% of R. dominica in June–July and 74% in August–September. At the 5-pair density, the numbers of F1 progeny per female were 44 and 51, during the first and second period, respectively while at the 50-pair release rate, only 6 and 7 individuals were recorded, respectively. In a second test, the effects of different materials used for storing were evaluated on both insects. Five hundred (500) grain-residing 20–22-day-old R. dominica larvae were mixed with 250g fresh wheat stored separately in each of five types of bags, i.e. jute, calico (Americana cloth), polypropylene, polythene, nylon, then exposed to 50 pairs of A. calandrae. The parasitoid suppressed host populations in all types of bags, except in those made of polythene. The highest percentage (69 and 81%) suppression occurred in calico bags during the June–July and August–September periods, respectively. The lowest suppression of 51 and 57% was observed for polypropylene bags during the respective periods. The parasitoid-induced mortality was positively correlated with the parasitoid density.

Field experiments on reduced application doses of Metarhizium anisopliae var. acridum (I 91 609: Zonocerus variegatus strain) were carried out in 1996–1997 in southeastern Benin and central Ghana. The first experiment, which took place in southeastern Benin, consisted of ULV applications of an oil based formulation of M. anisopliae on 1-ha plots of cassava, at the rates of 1 × 1011, 4.65 × 1011 2.5 × 1012 and 1 × 1013 conidia/ha. In a second experiment carried out in central Ghana, the application doses were reduced by increasing the space between spray tracks. Treatments were applied at 5, 10 and 20m track spaces, corresponding to doses of 2.5 × 1012, 1.25 × 1012 and 0.625 × 1012 conidia/ha, respectively. After application, samples of L4–L6 larvae and adults of Z. variegatus were collected using sweep nets and their mortality monitored in small cages. Zonocerus variegatus population density was monitored at three-day intervals over a 21-day period. In southeastern Benin, analysis of survival time, resulting from the first sampling, did not reveal any significant difference between the various dose treatments. In central Ghana, for treatments at different doses and track spaces, there was no difference between 5 and 10m track spaces, corresponding to 2.5 × 1012 and 1.25 × 1012 conidia/ha. But the 1.25 × 1012 conidia/ha treatment at 10 m-track space reduced the application time by half (17 min instead of 34 min).

Encarsia sp. is the main solitary endoparasitoid developing on the larvae of the cotton whitefly Bemisia tabaci (Gennadius), in western Burkina Faso. The biological control potential of this parasitoid is currently under investigation. Studies of some population parameters and biological control assays have been undertaken in the laboratory and greenhouse. Encarsia sp. can develop on the four larval stages of B. tabaci obtained in our study conditions, 7 to 15 days after oviposition. The highest rates of parasitism were recorded on the third and fourth larval stages of B. tabaci. The duration of Encarsia development was shorter on the third and fourth than on the first and second instars. The emergence rate of the F1 generation was high (>80%) and seemed not to be related to the different host stages. The sex-ratio favoured females (6:1). Encarsia adults have a relatively short lifespan (<5 days) and males live twice as long as females. In experimental cages, parasitism levels fluctuated over time, and significantly increased with the number of parasitoids introduced. This study constitutes an important advance in assessing the potential of Encarsia sp. for biological control of B. tabaci in cotton crops in Burkina Faso.

Cotesia flavipes Cameron (Hymenoptera: Braconidae) was introduced in Uganda in 1998 for the biological control of the old association cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). However there is little information on whether this parasitoid will attack new association Lepidoptera, which in turn may have implications on its efficacy on Ch. partellus. This study investigated the incidence of introduced Co. flavipes on Ch. partellus, and new association lepidopteran species and associated effects on its efficacy. Parasitism levels for Co. flavipes in several locations varied between 13.7–34.8% and 1.5–18.8% on Ch. partellus and new association hosts, respectively. Implications for biological control of stemborers in Uganda are discussed.

The three races of the honeybee Apis mellifera Linnaeus in Kenya (A. m. scutellata, A. m. monticola and A. m. litorea) differ from each other with respect to size, cubital index and abdominal colour banding pattern. These differences were used to assess the extent of interbreeding and hybridization between the races. This was verified on the basis of selected morphometric traits. Bee samples were collected from traditional log hives in seven geographical locations throughout Kenya ranging from lowland Mombasa in the coastal region to the highland Kinangop ranges. The length and width of the right forewing, length of proboscis, right antenna and right hindleg were measured, and the cubital index was computed for each specimen. The bees were classified according to size and colour banding pattern. Data analysis indicated there was hybridization among the three races of A. mellifera in Kenya due to swarming and migration under seasonal pressure.

Total and differential haemocyte counts following starvation and feeding resumption, ventral nerve cord transection, and brain implantation followed by methoprene application and 20-hydroxyecdysone injection were studied in Danaus chrysippus (Linnaeus) larvae. The results revealed that initial starvation and transection of the ventral nerve cord before the fifth abdominal ganglion in fifth instars of D. chrysippus led to a reduced total haemocyte count, on the one hand, and to a higher variation in percentage of different haemocyte types, on the other. While feeding resumption, brain implantation and 20-hydroxyecdysone treatments reversed the effect of starvation and nerve cord transection, methoprene application produced a decline in total number of haemolymph cells.