During the last decade damage to stone-and pome-fruit orchards in Israel caused by bark beetles has increased. We present data on injury by Scolytus amygdali Geur. and S. rugulosus Muller to nine rosaceous fruit trees of Prunus spp., Malus silvestris, Pyrus malus, Cydonia oblonga and Eriobotrya japonica in 6 major regions in Israel. Approximately 64 and 18% of the sampled areas planted with stone- and pome-fruits, respectively, were damaged by bark beetles. The heaviest damage occurred on apricot, almond, peach, plum and cherry. Most of the area planted with stone fruits, and large areas planted with apple and pear, were damaged by bark beetles. The most widespread beetle damage occurred in the central mountain range and the southern coastal region, with approximately 96 and 92% of the sampled area damaged, respectively and the least occurred in the northern mountain range. Stone fruits are more susceptible to damage by bark beetles than apple and pear, while quince and loquat are virtually resistant. The level of damage appears to be influenced by grove management, host plant resistance to Capnodis spp. (Coleoptera: Buprestidae), climatic conditions and conditions in plots neighbouring the orchard.

We monitored abundance, population dynamics and damage impacts of the leucaena psyllid Heteropsylla cubana Crawford (Homoptera: Psyllidae) in a maize-leucaena agroforestry system. The abundance of local ladybird beetle predator populations were also evaluated. The studies were conducted between June 1993 and November 1995 at Mtwapa and Amoyo in coastal and western Kenya respectively. Alley-cropping leucaena with maize had no effect on the abundance of the leucaena psyllid or its coccinellid predators. Therefore, neither the ‘resource concentration’ hypothesis nor the ‘enemies’ hypothesis corroborated for the psyllid-leucaena system within the spatial scale of this study. Psyllid populations were generally much higher at Mtwapa than at Amoyo, suggesting possible environmental effects on population growth. Psyllid populations were influenced by weather (mainly rainfall) and availability of suitable shoots. New growth of young shoots following rainfall encouraged psyllid abundance as long as weather conditions were not extreme. Though population of the generalist ladybird beetles was correlated with that of its psyllid prey, beetles did not appear to have significant effect on prey populations.

Populations of surface-living Collembola of a 5-year-old fallow were monitored with pitfall traps before and after clearing of vegetation, after ploughing and harrowing and during the different growth phases of cowpea (Vigna unguiculata L. Walp.) with and without weed-control measures. Overall, 8 genera of Collembola were identified in the study site. Songhaica nigeriana was the most abundant species in the study site before clearing. After clearing, the relative abundance of the different genera of Collembola was altered and after ploughing and harrowing, fewer species were recorded. After ploughing, Songhaica nigeriana, Dicyrtoma, Cryptophygus and Sminthurinus spp. were not obtained in the study site. During the vegetative growth phase, Collembola populations remained low in the herbicide-treated plots. The community structures of Collembola varied among the treatments, and temporal changes in the relative abundance of the different genera of Collembola were observed.

The blue biliverdin pigment in the haemolymph of Schistocerca gregaria Forskål (Orthoptera: Acrididae) was shown to be associated with all the stages and ages of the solitary-reared (solitarious) insects, irrespective of their origin or diet. The pigment was absent or present in very small quantities in the crowd-reared (gregarious) insects. The ratio of absorbance at 460 nm and 680 nm, the former representing the λmax for the carotenoid pigment and the latter for the biliverdin, provides a clear-cut index for partitioning the phases. The mean value of the index for the gregarious group fell in the range 3.69 to 4.78. That of the solitarious group ranged from 0.64 to 1.67. The absorbance ratio at 460/680 nm appears to represent a simple and convenient means of differentiating the two phases of the desert locust, Schistocerca gregaria.

Three designs of pheromone-baited flight trap for the larger grain borer, Prostephanus truncatus (Horn) were compared in a daily-trapping trial in Ghana. Japanese-beetle (JB)-type traps, composed of a funnel surmounted by a cross-vane, captured two to three times more beetles than delta- and box-type sticky traps, which are currently the most commonly used designs. Japanese beetle traps have now been adopted by the Ghana National Trapping Network for P. truncatus. The higher efficiency of the JB traps has led to the discovery of the borer in two important maize-growing areas which had previously recorded zero catches using sticky delta-type traps. Analysis of correlation between replicates suggested that JB traps were the most consistent of the three trap designs (r = 0.88). The mode of entry of P. truncatus adults into different trap types, which may explain variations in catches from the different traps, is discussed.

Competition between Dermestes maculatus Degeer (Coleoptera: Dermestidae) and Necrobia rufipes Degeer (Coleoptera: Cleridae) in Clarias gariepinus (Burchell), was studied at four population levels (16,30,48 and 60), three moisture-content levels (12,15 and 20%) and three temperatures (20, 27 and 32°C). Experiments were carried out using adult insects of both species in mixtures of equal and unequal numbers. Interspecific competition between N. rufipes and D. maculatus was found to have an effect on the population growth of both beetles but to different extents. The intensity of competition is dependent on temperature, moisture content and the initial density ratio. Using the replacement series approach, it was predicted that at high adult population and moisture content, N. rufipes becomes extinct and D. maculatus dominates a mixed culture. At a temperature of 20°C, D. maculatus outcompetes N. rufipes while at 32°C, both species co-exist. This observation possibly accounts for the low occurrence or absence of N. rufipes relative to D. maculatus in commercial dried fish in areas with temperatures of 20 to 30°C.

A basic study of the behavioural responses of the harvester termite, Hodotermes mossambicus (Hagen) to poison baits was undertaken. Laboratory trials revealed that the collected baits were not incorporated into the termite nest food stores. The baits were never eaten because the nest-bound larval caste selects the food to be consumed by the entire colony, from the material collected by the foraging caste. Moreover, field observations have shown that the commercial bait, Kamikaze®, bears no resemblance to the grass collected by the termite foragers. This study revealed that observations of foraging and feeding behaviour of the termites are necessary before designing control measures.

Studies were conducted from 1993–1995 at Samanko, Mali, on rearing and pheromone trapping of Busseola fusca Fuller (Lepidoptera: Noctuidae), and on the insecticidal effect of extracts of Jatropha curcas (Euphorbiaceae) on B. fusca and Sesamia calamistis Hampson (Lepidoptera: Noctuidae). A technique for mass rearingof B.fusca larvae on a chickpea and sorghum leaf-based meridic diet was developed, requiring about 10 g of diet per larva. An average of 7.3 successive generations were obtained per year. Pupal and larval mortalities were less than 15%. Oviposition was obtained on artificial substrates, with a fecundity of 300–500 eggs per female. Laboratory tests were conducted with diets in which extracts of nuts of J. curcas had been added. A 100% larvicidal effect was obtained with B. fusca and S. calamistis at 0.01% and 1% crude oil concentration respectively, and with 0.025% of the phorbol ester fraction on S. cahmistis. Trapping experiments using traps made of aluminum trays baited with synthetic pheromone showed that B. fusca male moths flights could be satisfactorily monitored. An improvement of traps and/or pheromone effectiveness is, however, necessary before their use as a control method.

Studies were conducted using a water-based trap baited with the synthetic female sex pheromone to gain further understanding on the effect of trap height and spacing in relation to crop height on catches of males of the millet stemborer, Coniesta ignefusalis (Hampson) (Lepidoptera: Pyralidae). Regardless of crop height, catches were greatest at trap heights of 0.10 and 0.50 m when the traps were stacked vertically. When traps were sited singly at 50 m spacing there was no significant difference in catches at the different heights. When trap spacing was varied from 50,15, 5,1 to 0 m, male moth catches in traps increased at lower trap heights, regardless of crop height. Comparison of catches in light traps and pheromone-baited traps showed a significant positive correlation. These findings have implications for both monitoring and development of millet stemborer control systems through mating disruption and mass trapping.

A study on the digestive carbohydrates complex was carried out in adult Zonocerus variegatus (Orthoptera: Pyrgomorphidae) to determine the status of the cyanogenetic glucose ingested by the grasshopper feeding on cassava. Two groups of adult Zonocerus were used. One group had been starved for 48 hours immediately prior to the experiment while the other had been fed continuously. After dissection, 10 to 15 portions of intestinal tracts (i.e. foreguts, caeca, midguts, hindguts) and 20 to 30 salivary glands were respectively crushed, centrifuged and dialysed for 24 hours in distilled water. The distillates obtained from different parts of the digestive system were used for determining the osidasic activities. Twenty-three substrates; i.e. 5 oligosaccharides, 10 synthetic heterosides and 8 soluble polysaccharides were selected for measuring the activities of the enzymes. Results showed that Z. variegatus has a wide range of enzymes whose activities differ according to different portions of the gut. The mid- and hind guts are the most active parts of the digestive tract but amylase activity was higher in the salivary glands. The Zonocerus variegatus osidase complex is characterised by the following proprieties: (a) high oligosaccharides activities on α-glucopyrones (maltose, saccharose) and on β-glucopyrones (cellobiose); (b)varied heteroside activities with α-glucosides and linamarase very active; (c) amylase activity very high, and hemicellulase and cellulase activities very low. In Zonocerus, starvation increases maltose hydrolyse but it does not affect other oligosaccharide activities. On the other hand, starvation reduces most of carbohydrases activities. The origin and consequences of the linamarase activity in the insect gut are also discussed.

The total number of eggs laid by Callosobruchus rhodesianus (Pic.) and Callosobruchus maculatus (F.) females in the presence of single and mixed species populations of males at different densities were counted. Increasing male density significantly reduced the realised fecundity of C. maculatus but not C. rhodesianus females. In the presence of C. maculatus males, however, the number of eggs laid by C. rhodesianus was greatly reduced. The reduction in egg laying and observations on mating behaviour indicates direct physical interference between weevils and competition for mates. An adequate number of beans were provided so competition for oviposition sites by females was unlikely. The ability of C. maculatus to inhibit oviposition of C. rhodesianus is suggested as one reason for its superiority over the latter when the two species compete for limited resources.

In quantitative feeding experiments, larvae of Grammodes stolida (Fab) consumed significantly more of mature leaves than young and senescent leaves of Lannea coromandelica (Houtt). The maximum leaf consumption was by the third instar. The amount of food consumed by the penultimate and final instars comprised 72.6% of the total larval consumption. Food utilisation indices, namely approximate digestibility (AD), efficiency of conversion of ingested food (ECI), and efficiency of conversion of digested food (ECD) showed a significant decrease during the second larval stage. The bionomics of the moth were studied in relation to its survivability and reproductive potential on Lannea coromandelica which appears to be a potential host which the pest could colonise during periods of non-availability of other crop hosts.

The effect of hexaflumuron, a chitin synthesis inhibitor, on the mating success of three species of vector mosquitoes, namely Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi, was investigated. The three species were exposed to concentrations giving 5% and 50% inhibition of emergence (EI5 and EI50, respectively) at the fourth instar and to 0.005 and 0.05 mg/1 hexaflumuron at the pupal stage. Emergent adults were allowed to mate with each other and with their untreated counterparts. Reduction in mating (evaluated as % insemination) was highest in Ae. aegypti exposed at the larval stage. Mosquitoes exposed at the pupal stage to 0.05 mg/1 hexaflumuron showed higher reduction in mating than those exposed to 0.005 mg/1. The effect of hexaflumuron appeared to be cumulative, resulting in a 78–80% reduction in % insemination when treated males were mated with treated females, compared with untreated males mated with untreated females.