The biology of two African sweetpotato weevil species, Cylas puncticollis and C. brunneus (Fabricius) (Coleoptera: Apionidae), was studied in laboratory experiments carried out at 27 ± 1°C, 45 ± 5% RH, and a 12 h photophase. Cylas puncticollis females lived longer than C. brunneus (141 ± 10 and 92±12 days respectively), developed faster (egg to adult 20–28 days, and 32–41 days respectively) and had a lower oviposition rate (1.10 ± 0.04 and 1.53 ± 0.06 eggs per female per day respectively). The total egg production per female (average 101), sex ratio (1:1) and proportion of eggs surviving to adulthood (average 89%) were similar for both species. The intrinsic rate of increase was higher for C. puncticollis (0.553 per 10-day period compared to 0.521 for C. brunneus). Under field conditions C. brunneus will benefit from its higher oviposition rate during periods of favourable conditions for sweet potato weevils, like dry spells which expose tubers for egg laying. Cylas puncticollis will benefit from its longer longevity during less favourable conditions, as females can survive extended periods when no oviposition sites are available and then resume egg laying when conditions improve.

The effects of egg clutch size on development and survivorship of the larger grain borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) on maize were measured in the laboratory using single grains of the white maize variety, TZSR-W, at 30 ± 2°C and 70 ± 5% RH. Varying numbers of P. truncatus eggs (1, 2, 4, 8, or 16) were introduced into a hole drilled into a single maize grain. Destructive sampling was used at regular intervals to obtain data on immature developmental parameters, the location of immatures within the grain and the weight and sex of any emerged adults. First instars fed mainly on the floury endosperm tissue whereas the second and third instars preferred the germ tissue. Mortality due to competition was highest in first instars. At high initial densities (> 4 per kernel), some P. truncatus larvae reduced competition by moving out of the grain. A maximum of 6 adults emerged from a single grain. The mean number of adults that emerged per grain for initial egg densities of 8 and 16 were 3.3 and 3.5, respectively. Prostephanus truncatus adult weight at emergence was not significantly influenced by initial egg density except in the case of clutch size 16. The sex ratio of emerged adults was also unaffected by competition, and was always 1:1. Complete developmental period within grains ranged between 28 and 32 days.

A wide variety of Hemiptera species are found on the leaves of palms in humid tropical zones. Many of them are highly polyphagous, and generally once adult, only accidentally end up on palm leaves, on which they can nevertheless feed. Other hemipterans spend the whole of their developmental cycle on palms, and some seem to live on palms alone. Most of the Hemiptera have no economic impact on their hosts, since their population levels are rarely high enough to cause significant damage. However, some Heteroptera: Coreoidea and Homoptera: Coccoidea species can be very damaging primary pests. Others amongst the Homoptera: Fulgoroidea, Cicadelloidea and Heteroptera: Pentatomoidea transmit serious diseases that have decimated oil palm and coconut plantations, for example coconut lethal yellowing in Africa and the Caribbean, and oil palm and coconut trypanosome diseases in Latin America. Lastly, some Heteroptera: Pentatomoidea and Reduvioidea species are natural enemies of lepidopteran caterpillars.

Various trap designs were tested in Congo in order to assess their cost vs. effectiveness for the control of human trypanosomiasis vectors. These preliminary trials indicated that it is necessary to compare the different trap designs in several African countries. Furthermore, studies on the attractiveness of locally available fabrics must be carried out in order to make traps taking into account the sizes of locally available fabrics. At present, the ‘Vavoua’ trap is sail the most efficient but further investigations need to be carried out to reduce the cost of new traps without significantly affecting their efficiency. The ‘black/blue/black’ screen can be used successfully by rural communities in Congo for tsetse control.

Participatory trials on the use of a mycoinsecticide based on spores of the entomopathogenic fungus Metarhizium flavoviride were carried out to control grasshoppers on farmers' plots at Gouré, Niger. The study was conducted in collaboration with the natural resources management project financed by Africare. From a fallow area of about 800 ha, six plots of 5 ha each were selected. Three of these plots were treated with M. flavoviride, strain IM 330189, while the three remaining plots served as controls. An emulsion of the fungus was prepared with 50 g of dry spores mixed with paraffin and ground oil at a ratio of 7:3. This formulation represents a concentration of 2.5 × 1012 spores per litre. The mycoinsecticide was applied at the rate of 2 litres/ha with a Micron ULVA sprayer. Immediately after spraying and three days later, two batches of 50 L4 and L5 Oedaleus senegalensis larvae were collected per plot and each batch kept in a separate cage. One of the two cages was kept in the experimental plot, whereas the second one was taken to the station, in order to follow the grasshoppers' mortality. Cages were checked daily for two weeks starting from the day of fungus application, and insect mortality recorded. Dead insects were transferred into Petri dishes with moistened filter paper to allow the fungus to sporulate from the cadavers. Grasshoppers kept in cages suffered 80% mortality, 12 days after application. Reduction in grasshopper population density between treated and untreated plots was significantly different, but did not convince farmers, as full grown L5 larvae had emerged as adults and began migrating. However, cadavers collected from cages containing insects from treated plots allowed farmers to follow how the fungus sporulates and contaminates healthy grasshoppers. Farmers were interested in the product but were reluctant to buy a slow-acting insecticide.

Larvae of Cirina forda (Westwood) (Lepidoptera: Saturniidae), a popular food insect in the southern parts of Nigeria were raised in the laboratory on cut foliage as well as on a growing Vittelaria paradoxa tree at the University of Ilorin, Nigeria. Comparative observations were made on the insect's biology and behaviour in both rearing systems in order to ascertain if the larvae could be reared in captivity on cut foliage. Egg eclosión began 24–48 hours after egg-laying and lasted 10 days. First instars initially aggregated after egg hatch, then migrated in single file to feed after approximately 12 hours after emergence. The first and second instars fed as an aggregate, while the third and subsequent instars fed separately. The first two instars did not exhibit any defensive response when disturbed, but the subsequent four instars emitted a green fluid which may act as a repellant to potential predators. High mortalities were suffered by the first and the penultimate instars. Results have shown that Cirina larvae could be easily reared artificially on V. paradoxa to serve as source of food for humans.

In experiments to select a character for identifying larval instars in Sesamia calamistis and Eldana saccharina, body length, body width and head capsule width were measured in populations reared on artificial diet. Seven instars were found in S. calamistis and 5 in E. saccharina. For both species, body length was determined to be the best characteristic to distinguish instars because it was easy to measure and had the smallest error.

A laboratory study of the dietary preferences and duration of food plants in the gut of Zonocerus variegatus was carried out using three plant species, namely Manihot esculenta, Vernonia amygdalina and Chromolaena odorata. Whole or cut up plants were offered to the grasshopper in the experiments. Overall, whole V. amygdalina was the preferred diet of Z. variegatus, while the insect ate cassava pieces better than whole plant. Chromolaena odorata was the least preferred diet of the three. The duration of the food plant within the insects' gut was shortest for V. amygdalina, which was consumed all at once soon after being offered to the insects. The insects consumed cassava in two successive sessions and C. odorata in three. The total time spent eating was similar for V. amydalina and cassava, which were significantly shorter than that spent eating C. odorata. Evidently, V. amygdalina could serve as a good bait plant for Z. variegatus. However, its status as a human food plant precludes its use as a bait followed by chemical control; it may be used with, for example, fungal biocides such as Metarhizium.

The biological activity against Boophilus microplus of extracts of the berries, bark, leaves and twigs of Pimenta dioica was examined and compared with that of eugenol, methyl eugenol and four commercial acaricides, namely dimethoate, farnesyl methyl ether, carbaryl and diazinon. The berry essential oil was more effective at inhibiting oviposition and causing mortality of the ticks than all the extracts, the commercial acaricides and methyl eugenol. At a dose of 1.0 mg/g it was 33, 12, 6, and 3 times as effective in inhibiting oviposition as the non-polar extracts of the leaves, bark, twigs and berries, respectively. The potency of the berry essential oil is attributable to eugenol, a phenyl propanoid derivative, which accounts for over 65% of the oil content.

The relationship between axil age and water-holding capacity on the presence and age of immatures of Aedes (Stegomyia) simpsoni (Theobald) complex (Diptera: Culicidae) in cultivated banana, Musa spp. (Musaceae), Colocasia esculenta and Xanthosoma sagittifolium (Araceae) during the rainy and dry seasons at different locations in Uganda is presented. On Masa spp., higher, younger axils were found to contain more water than older Ones. In some seasons these axils held more immatures of Aedes simpsoni complex than the lower, older axils of the plant. On C. esculenta and X. sagittifolium plants, the middle and lower axils held more water, and had a greater abundance of larvae and pupae. There were generally no significant differences (P > 0.05) in the mean age of larvae and pupae found in axils of different ages.

Cassava varieties resistant to the cassava green mite, Mononychellus tanajoa (Bondar) ( Acari:Tetranychidae) have been reported in many parts of Africa where the pest has been introduced. However, the resistance mechanisms have not been identified. Laboratory studies on biology and feeding behaviour of cassava green mite were carried out at the International Institute of Tropical Agriculture (IITA), in order to determine whether this resistance is mainly due to pubescence.

Cassava pubescence was found to have no antibiotic effect; both pubescent and non-pubescent varieties were preferred by the mite for oviposition, food and shelter. In addition, pubescence does not afford a mechanical barrier to cassava against green mite infestation.

One hundred forty-nine Anopheles gambicie s.l. and 260 A. funestus were collected from the field in Namawala, Tanzania in June 1994. The mosquitoes were dissected and examined for plasmodium oocysts using two microscopic techniques and the polymerase chain reaction (PCR) method. The oldest and simplest technique, the saline test, detected oocysts in 94 out of the 97 mosquitoes found to have oocysts by the more sensitive merbromin stain and PCR techniques. The saline test was found to be a sensitive and reliable field technique for detection of large Plasmodium oocysts in mosquitoes. The merbromin staining technique was as sensitive as PCR, detecting even small oocysts.

The dispersal characteristics of a population of 124 marked adult individuals (62 males and 62 females) of the armoured ground cricket (AGC), Acantliophis speiseri Brancsik (Orthoptera: Tettigoniidae, Hetrodinae), released at the centre of a circular study site, were investigated using the capture-mark-release-recapture method for five successive days. The 110 m-diameter study site comprised five grass-trap annuii (each 1 m wide) spaced at 10-m intervals from the centre.

The frequency curve of numbers derived from recapture data for day 1 departed from normal (Kurtosis = 2.7), indicating that the released AGC population was heterogeneous in its dispersing behaviour. A comparison of mean numbers of recaptures from grass-traps per quarter portion of the study site revealed no drift in the dispersal of the population (P > 0.05), though differences in the variances of the recapture frequencies indicated a tendency towards non-random movement in the AGC population.

The population covered a mean distance of 24.47 m in the first 24 h following release and the rate of dispersal changed daily in the five-day study. The implications of the dispersal characteristics observed in this study to future design of control strategies for the pest in Zambia are discussed.

Two types of failures of attack by the top borer, Scirpophaga excerptalis Wlk., and their relation to sugarcane resistance to deadheart formation were studied in 164 genotypes of sugarcane for three years at two locations, viz., Karnal (Haryana State) and Chakia (Bihar State) in India. Attacks were unsuccessful either because of failure of neonate larvae in the mid-rib to reach the spindle (Type 1) or failure of older larvae in the spindle to reach the meristem (Type 2). Type 1 failure was frequent (19.2 to 26.7 %) while Type 2 was rare (2.9 to 5.1 %) among the genotypes. Larval dispersal and mortality were influenced by several factors related or unrelated to resistance and occurred concurrently in the same genotypes. This led to variation in larval mortality even among genotypes with the same levels of Type 1 failure. Those genotypes (Co 1223, Co 1224, E 276, Co 7224, Co 745, E 128, Co 62235, E 132, E 50, CoS 767 and CoJ 67) that had high scores of both Type 1 failure (14 to 18) and larval mortality (13 to 17) had the lowest percentages of deadhearts (11.8 to 24.4%).

Type 2 failure was not related to resistance; the highly resistant genotypes, Co 1223, Co 1224, E 276, Co 62235, E 132, CoS 767 and F133, showed no Type 2 failure. Furthermore, genotypes IA 3017 and Co 7322 which had the highest Type 2 failure scores of 9 and 12 respectively, had 61 and 36% deadhearts respectively. It is concluded that Type 2 failure may be caused by larval mortality in the spindles due to diseases and/or asphyxiation by accumulated rain water.

Tannin extracts of two sorghum, Sorghum bicolor (L.) Moench. cultivars, BKS5 and BTX 623 were assessed for their bioactivity against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and the angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), in whole wheat flour pellets, and against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in whole wheat flour at three treatment levels. The number of adult progeny was reduced and number of days to emergence increased by tannins extracted from both sorghum cultivars at all treatment levels. However, the effects were not significant in all cases. In a short-term (25 days) feeding test using S.oryzae adults, the presence of sorghum tannins from cv. BKS 5 in the pellets significantly reduced feeding by the insects.

Soil samples collected from six localities in Pakistan—Peshawar, Quetta, Loralai, Sibi, Lahore and Sheikhupura—were screened for insecticidal Bacillus spp. Bacillus coagulane, B. megaterium and B. alvei, which constituted 50%, 33% and 17% of the Bacillus isolates respectively, were isolated and their toxicity was evaluated against larvae of the house fly, Musca domestica (Diptera: Muscidae). The most toxic bacterial isolate of the three was B. alvei (98.7% mortality) and the least toxic was B. megaterium (89.3% mortality). Extracts of experimental larvae showed the presence of strains of the respective species of Bacillus in all cases, indicating that the observed mortality in the house flies was caused by the Bacillus species.

Studies of cocoa tree genetic resistance to attack by Scihlbergella singularis (Haglund.) (Hemiptera: Miridae), have so far been based on field observations of cultivar performance. Although this approach was useful in guiding breeding programmes, observations on tree crops are time-consuming (3–4 years) and labour-intensive. Thus a standard laboratory microassay method based on a study of the mirids’ dietary preferences was developed to quantify the attractiveness of cocoa trees to mirids under controlled conditions, with reproducible results.

A dual approach was taken to establish relations between laboratory data and field observations: preliminary cultivar sorting of both clones and hybrids in the laboratory, by microassays was combined with an eight-year observation programme in two different ecological zones in Ivory Coast: on the shores of a lagoon (Bingerville) and under thinned forest in Basse Côte (Divo). In Cameroun only clones from IRA field station at Nkoemvone were tested by microassays.

After three successive sets of field observations, a comparative analysis of the results revealed close correlations between cultivar responses in microassays and those observed in the field.

Cultivar responses to mirids revealed that there are two performance groups within the planting material selected, viz., in increasing order of attractiveness, Forasteros (upper and lower Amazon cultivars) and Trinitarios.

In Cameroon, microassays revealed behavioural polymorphism amongst the cultivars tested: plants of the same origin can react very differently to mirids as it was the case for the local trinitarios SNK group.

The microassay technique is quick and easy to use, and is effective for the early selection of mirid-tolerant plant material.

In laboratory studies on the nymphal and adult performance of the cotton stainers Dysdercus cardinalis and D. fasciatus (Pyrrhocoridae: Hemiptera) on seeds of five different host plants, two categories of hosts with significantly (P < 0.05) different biological effects were identified. Gossypium hirsutum L., Ceiba pentrandra Gaertn and Sterculia rhynchocarpa (K. Schum) were found to be suitable hosts (category A) while Adansonia digitata L. and Abutilon mauritianum (Jacq. Medic.) were unsuitable (category B). Category A hosts that grew in the wild appear to serve as perennial breeding reservoirs for the cotton stainers and thus play a significant role in initiating and perpetuating their infestation of adjacent cotton crops. The converse appears to be true for category B hosts, whose long-term effect would be to gradually decrease the population of the cotton stainers.

Investigations were conducted in six farm fields (1.5 to 3 ha each) in Burkina Faso with objectives to (1) study adult Smicronyx spp. (Coleoptera: Curculionidae) population dynamics during Striga hermonthica (Scrophulariaceae) seed-pod production, (2) assess the impact of different population levels of Smicronyx spp. on St. hermonthica capsule production and, (3) estimate Smicronyx female reproductive success in seed-pod galls. A Univac portable sampler was used to sample adult Smicronyx spp. and St. hermonthica densities were assessed using aim2 metal quadrat. Fifty St. hermonthica shoots per field were sampled each week. Before the emergence of St. hermonthica, Smicronyx adults were found on nearby Striga éspera (Willd) Benth. fields. Striga hermonthica shoots produced on average ca. 24 seed capsules each, while each female Smicronyx galled from 12 to 32 seed pods. Seed-pod galling alone was not sufficiently high to be considered as a successful reduction factor for St. hermonthica seed production in natural conditions. Smicronyx spp. adult population levels decreased during the St. hermonthica capsule production period. Increased population levels of Smicronyx spp. resulted in higher percentages of St. hermonthica seed-pod galls, suggesting that a ugmentative techniques, if used as part of an integrated control programme could be a worthwhile strategy.