The chemical nature of the repellent secretion of the African grasshopper, Zonocerus variegatus (Orthoptera: Pyrgomorphidae) reared on Acalypha wilkesiana L. and Manihot esculenta (Crantz) was analysed. It was found to contain alkaloids, glucose, proteins, free amino acids, trypsin-like proteinase, carbohydrases, lipase and the ions Ca2+, Mg2+ and K+ but not Na+ and (PO4)2-. Alkaloids were present in the secretion whether or not the insect was fed on plants containing alkaloids. Cyanide ions were absent in the secretion, even when Z. variegatus was fed exclusively on the cyanogenic Manihot esculenta. The amino acid and glucose contents were the same in grasshoppers reared on different plants. The protein content in the repellent secretion was constant, despite the fluctuations observed in the protein content of the haemolymph.

The effect of N, P and K fertilisers, measured as percentage leaf dry matter, was assessed on larval populations of Maruca testulalis (Geyer) (Lepidoptera: Pyralidae) recorded on cowpea, Vigna unguiculata, var. IT 82E-32 under natural infestation. The study was carried out during the 1987 long rains (March-July), at Abomey-Calavi's experimental farm. A factorial experiment with 9 completely randomised treatments in three replicates of N-P-K fertilisers was used. Phosphorus was applied at three levels (P0, P1, and P2) corresponding to 0, 40 and 80 kg of P2O5/ha respectively. Potassium was also applied at three levels (K0, K1 and K2) representing 0, 40, and 80 kg K2O/ha respectively. In all plots nitrogen was applied as 20 kg /ha of urea. All the fertilisers were spread on the soil on the day of planting. Fourteen sampling dates for flushing shoots, flower buds, flowers and pods were subsequently made 29, 33, 36, 40, 43, 47, 50, 54, 57, 61, 64, 68, 71 and 75 days after sowing (DAS) to evaluate the infestation rate by M. testulalis larvae. Sampling for. N, P and K contents in cowpea leaves was conducted 29, 47 and 61 DAS. As for interaction between P and K and the pest, only the averages of larvae from interaction P0 K0, P2 K0 and P0 K1 on the one hand, and those from the interaction of P0 K0, P0K2 and P0K2 on the other hand, were statistically, (P < 0,05) different. Multiple regression analysis showed that the content of N, P and K in cowpea leaves throughout the sampling period influenced by 40% the total variation of larval population of M. testulalis in the plant. The remaining 60% were due to other factors of experimental agrosystem. Application of N, P and K fertilisers to the cowpea and their assimilation by the plant are primarily aimed at increasing the plant vigour and grain yield. In contrast, the plant vigour induced by these nutrients leads to an increase in the larval population of M. testulalis in the plant and also to a decrease in the highest yields that can be expected from the use of these fertilisers. Therefore, an agrobiological competition takes place as a result of two inductive opposite effects inherent from fertilisation. In connection with this situation, the control of M. testulalis using fertilisers could be one option to maintain a buffer effect between the pest and the plant, thus therefore help in increasing cowpea yield.

Three field trials were conducted to determine the effect of various levels of resistance of South African sorghum hybrids on follow-up generations of Busseola fusca Fuller (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae). In one trial, plants were artificially infested with B. fusca larvae while the other trials were subjected to natural infestation of C. partellus. The number of damaged internodes and moth exit holes per stem were used to calculate a relative survival index which estimates the survival of larvae to the adult stage. A moth production index was calculated to estimate the role of a hybrid in area-wide suppression of stemborer populations. In the B. fusca trial, resistant and susceptible experimental hybrids produced 40 000 and 113 000 moths per hectare respectively, compared to 80 000 and 83 000 moths per hectare produced by the commercial hybrids. Larval damage to whorl leaves, assessed on a 1 to 9 scale, indicated leaf-feeding resistance of commercial hybrids to B. fusca ranging from susceptible to intermediate. Yield losses suffered by the hybrids in the B. fusca trial were greater than that suffered by a susceptible experimental hybrid, indicating susceptibility of South African hybrids to B. fusca. The evaluation of sorghum varieties for their potential to reduce stemborer populations should indicate their usefulness in integrated pest management systems.

The circadian activity of adults of Smicronyx guineanus Voss (Coleóptera: Curculionidae) was studied in semi-field conditions. Pairs of weevils were observed on a 24-h cycle starting from 0800 to the following day at 0600 hrs for 21 days in cages containing Striga hermonthica (Del.) Benth (Scrophulariaceae) plants parasitising sorghum. Each female and male was observed every second hour. Occurrences of the various behaviours exhibited by the weevil were recorded. In decreasing frequency, the weevils were observed to be standing still, feeding, mating, walking, moving and foraging. In addition, the difference in time spent on the different parts of the host plant—classified into four groups: A- stem, leaves and bud; B- corolla; C- calyx; and D- sorghum, petiole, soil, capsule and cage—was highly significant (P = 0.0001,10 couples/days, n = 21 days). The weevil adults spent 46.8% of their time on the Striga inflorescence (bud, corolla and calyx). Striga plants were also stratified with respect to distance from the base and categories were designated as upper, central and lower parts. Smicronyx adults spent 85.2% of their time in the upper stratum, 9.8% in the central stratum and 5% of their occurrences were in the lower third of the Striga shoot. They were more active during daytime, suggesting that the best period of day to sample the weevils in the field is from 0700 to 1100 or from 1600 to 1800 hrs.

In a study to determine the costs of tsetse trapping in terms of construction materials, labour, transport and maintenance, two hundred forty-six traps used to control Glossina pallidipes in an area of 100 square kilometres at Nguruman, Kenya were evaluated from November 1990 to July 1992. The total cost of materials, labour and servicing per trap per year, was US$ 30.6 which, at that time was equivalent to 1071 Kenya shillings.

Diet change in the cotton stainers, Dysdercus cardinalis and D.fasciatus, occasioned by their migration from Gossypium hirsutum (cotton) to alternate hosts Sterculia rhynchocarpa and Adansonia digitata, was overall beneficial to their bionomics. Only the host Abutilon mauritianum appeared to possess antibiotic effects against the fecundity, fertility and longevity of the stainers. The occurrence in tropical natural ecosystems of both suitable and unsuitable hosts appears to constitute a vital and a viable stainer population-regulatory mechanism. Overall, D. cardinalis exhibited superior reproductive parameters on a variety of diets than did D. fasciatus. The latter apparently suffered profound negative effects on its bionomics when feeding on certain hosts.

In olfactometer assays, the predatory mite Amblyseius ciicumeris (Oudemans) recorded a significantly higher response to volatiles from chrysanthemum, Denranthemct morifolium plants infested with western flower thrips (WFT), Frankliniella occidentalis (Pergande) than to volatiles from healthy plants. This increased attraction was attributed to the presence of higher amounts of Germacrene-D in WFT-infested plants. In choice experiments using synthetic volatiles, the predator remained longer in the olfactometer treated with 50 ng Germacrene-D and made many entries at 500 mg.

Preferential attraction of WFT to healthy chrysanthemum flower buds was observed, and attributed to the significantly higher amounts of (E)-β-farnesene found in the buds compared to leaves and open flowers. This attraction peaked at 100 ng/μl (E)-β-famesene. In greenhouse experiments, blue sticky traps with 500 ng (E)-β-farnesene or 1000 mg p-anisaldehyde attracted 32.3% and 27.5% more WFT than the untreated controls, respectively.

The prospects of using Germacrene-D in improving the attraction of A.cucumeris to whole chrysanthemum plants and (E)-β-farnesene in monitoring WFT, are discussed.

Isolates of Beauveria bassiana (Balsamo) Vuillemin, Paecilomyces farinosus (Holm ex SF Gray) Brown and Smith and Verticillium lecanii (Zimmermann) Viegas were evaluated for their pathogenicity to adults, eggs, first and third instars of silverleaf whitefly, Bemisia argentifolli (Bellows and Perring) (Homoptera: Aleyrodidae). Conidial dilutions were prepared in 0.05% Tween® and leaves treated by immersion in these suspensions. Assessments of nymphal infection were made 2, 3, 5, 7, and 10 days post-treatment. Infection rates in adults and eggs were made 14 days post-treatment. All isolates were pathogenic to nymphs and adults. None of the isolates were pathogenic to eggs. Isolates L3444 (P. farinosus) and L3009 (B. bassiana) were the most pathogenic to first instars and adults with LC50 and LC90 values of 7.3 × 104 and 3.1 × 106 conidia/ml, and 1.3 × 106 and 1.0 × 107 conidia/ml, respectively. Isolate FR20 (V. lecanii) was the most pathogenic to third instars with LC50 and LC90 values of 4.8 × 103 and 7.4 × 105 conidia/ml, respectively. Results imply that L3444 and L3009 are the most efficient isolates, based on their pathogenicity to first instars and adults. Results are discussed in relation to using fungi for management of silverleaf whitefly in greenhouses.

The influence of three cultivars of Sorghum bicolor (L.) on the activity of the fungus Metarhizium anisopliae on the stemborer Chilo partellus was investigated in the field and laboratory. Fungal activity in the field varied with the plant cultivar and the inoculum concentration. Larvae fed on different cultivars and inoculated with the fungus in the laboratory did not vary in their susceptibility to the pathogen. However, time to 50% mortality (LT50) of the larvae was shorter in cultivar IS 1044 than in cultivars ICS 3 and ICS 4. Compatibility of the fungus with cultivars is therefore an important consideration when using fungi for the biological control of stemborers.

The influence of gibberellic acid (GA3), a plant growth regulator (PGR), on the protein, total lipid, total carbohydrate, glycogen and trehalose contents of the banana fruit fly, Zaprionus paravittiger (Godbole and Vaidya) (Diptera: Drosophilidae), was investigated by feeding 63-h-old larvae on artificial diet containing 1000, 2000 and 4000 ppm GA3 for 30 and 50 h. The maximum increase in the protein content was recorded for the 1000 ppm GA3 treatment. Significant decreases in the total lipid and total carbohydrate contents were recorded at 1000 and 2000 ppm while the 4000 ppm treatment significantly increased their levels. Glycogen content was significantly decreased by all the tested GA3 concentrations. The possible reasons for the observed changes in these biochemical components are discussed.

Gas-liquid chromatography was used to analyse the saponifiable and unsaponifiable fractions of petroleum ether (PE) extracts of neem fruits and leaves. Both fractions, as well as a crude PE extract, were assayed for biological activity against third instar cotton leafworm, Spodoptera littoralis.

In neem fruits, eighty-eight percent (88%) of the saponifiable matter consisted of saturated fatty acids, while 12% was composed of unsaturated fatty acids. In the neem leaves, the corresponding proportions were 62 and 38%, respectively. Unsaponifiable matter of both fruits and leaves contained varying amounts of hydrocarbons and sterols. All the tested extracts demonstrated significant larvicidal effects against leafworm larvae. They also prolonged larval duration, caused malformations of the resulting pupae and significant adverse effects on the fecundity of resulting adults.

S2 line and S2 test-cross recurrent selection procedures were initiated to improve the resistance of a maize (Zea mays L.) population to the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae). Thirty-five selections developed from the population were evaluated for resistance to the stemborer in western Kenya. Resistance was rated according to leaf feeding (LF), stem tunnelling (ST) and deadheart formation (DH) following artificial infestation with first-instar C. partellus. Larval establishment and growth were also assessed. The reduction in foliar damage ratings, percentage stem length tunnelled, and percentage of plants showing deadheart after one cycle of recurrent selection were 4.38 %, 74.80 % and 13.92 %, respectively. A very low larval establishment on all the selections was attributed to their resistance to C. partellus attack. Results from this study indicated low levels of larval growth and development. It is concluded that antibiosis was the type of resistance mechanism against C. partellus in the maize populations investigated and that more cycles of selection are required to significantly shift the gene frequencies for resistance.

Laboratory experiments on the role of humidity, density and species of prey were conducted in order to better understand the ecology of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae), a predator introduced into West Africa to control the larger grain borer, Prostephanus truncatus. Developmental time of T. nigrescens was very similar among individuals exposed to 30,40, 70 and 90% relative humidity at 30°C, although survivorship varied. At optimal temperature and humidity larvae fed only first-instar Sitophilus zeamais as prey took longer to develop and weighed less at emergence, than those raised on first-instar P. truncatus. Larvae feeding on Tribolium castaneum took longer to develop with only 10% surviving to the adult stage. None of the larvae offered Gnatocerus maxillosus as prey survived. In an analysis of prey consumption rates, no T. nigrescens larvae survived on one P. truncatus first-instar larva per day; 50% survived on two per day, and almost 90% survived on five larvae per day. In an analysis of density effects on T. nigrescens reproduction and survivorship, there was no difference in the number of Fl offspring at T. nigrescens:P. truncatus ratios of 15:300,30:300,60:300 or 90:300, suggesting that the lowest predator: prey production ratio was the most efficient one.

The effects of diet on quantitative nutritional indices were measured in fifth-instar female nymphs of the grasshopper, Euprepocnemis plorans. Analysis of the main and interactive effects of feeding on the host plants lupine (Lupinus termis), horsebean (Vicia faba) or clover (Trifolium alexandrinum) and some of the plants' allelochemicals indicated that nymph performance was adversely affected by the hydrogen cyanide (HCN) and quinolizidine in horsebean and lupine respectively. Assimilation of clover was higher than of lupine or horsebean. Relative growth rate (RGR) was significantly higher in grasshoppers fed on clover than in those fed on either lupine or horsebean. Relative consumption rate (RCR) was in the order lupine > clover > horsebean. The efficiency of the digested and ingested food conversion were significantly lower in grasshoppers fed on lupine or horsebean than those fed on clover. The duration of the fifth instar was in the order horsebean > lupine > clover. Grasshoppers fed on horsebean or lupine lost weight during the experiment, with a greater weight loss recorded in those fed on horsebean. Grasshoppers contained the highest concentration of haemolymph proteins when fed on clover. Short-term feeding on lupine and horsebean resulted in 10 and 20 % mortality respectively, and nymphs that died on a horsebean diet were malformed.

Topical application of crude ethanol extracts (CEs) of the leaves of 43 of 51 Jamaican plants produced varying degrees of multiple acaricidal effects on engorged Boophilus microplus Canst., including mortality (M), inhibition of oviposition (IO) and inhibition of embryogenesis (IE). Acaricidal indices (AI) ranged from 50 to 100 for the CEs of 29 plants, 38 to 47 for 9 plants and from 0 to < 25 for 13 plants. The most active CEs, in decreasing order of activity (AI values in parentheses) were those of: Simarouba glauca (100), Symphytum officinale (99), Nicotiana tabacum (95), Hibiscus rosa-sinensis (93), Ervatamia divaricata = Ricinus communis (82), Salvia serotina (80), Stachytarpheta jamaicensis (79), Blighia sapida = Ocimum micranthum (76), Spigelia anthelmia (75), Cycloptis semicordata (74), Mormordica charantia (71), Bontia daphnoides (69), Azadirachta indica (68), Capsicum annum = Catharantus roseus = Petiveria alliacea (66), Gliricida sepium (64), Lippia alba (62), Cuscuta americana = Erythrina corallodendrum (61), Piper amalago (60), Cannabis sativa = Cecropia peltata (58), Dioscorea polygonoides (56), Artocarpus altilis (53), Crotalaria retusa (51), Citrus aurantium (50).

A method of formulating granules from an acetone extract fraction of the fruit of Melia volkensii, a Kenyan tree known to possess insecticidal properties, was developed. The granules were tested for toxicity to third and fourth instars of Aedes aegypti L. Some acute physiological effects were observed within 24 hours of adding the granules to water as larval food. A mortality of 95% was achieved on various developmental stages of the mosquito after 12 days, with only 5% adult emergence being recorded.

In leaf disc choice assays and topical application experiments, the neem (Azadirachta indica) limonoids azadirachtin, salannin, deacetylgedunin, gedunin, 17-hydroxyazadiradione and deacetylnimbin were found to be potent antifeedants and growth inhibitors to the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Azadirachtin was most potent in both respects. Gross dietary utilisation (efficiency of conversion of ingested food) of H. armigera was also decreased following topical application as well as after treatment in the diet. Growth inhibition in topically treated H. armigera may be primarily attributed to decreased food intake. The antifeedant and growth-inhibitory effects of the neem limonoids are discussed.

Laboratory studies were conducted to assess the toxicity and growth-inhibitory activity against Aedes aegypti larvae, of the crude acetone extracts of Polygonum senegalense (Meissn.) leaves, its flavonoid component 2',6'-dihydroxy-4'-methoxydihydrochalcone and the internal tissue flavanol quercetin. The first two showed significantly high insecticidal and growth-inhibitory activity even at low concentrations, whereas quercetin was toxic only at concentrations above 7μg/ml.

Effects of adult nutrition were investigated by measuring female longevity, body weight, fertility and ovariol yield in the grasshopper, Euprepocnemis plorans reared on 3 different host plants. Rearing the insect on lupine (Lupinus termis) and horsebean (Vicia faba) caused significant reduction in fertility and ovariol yield of its first and second pods compared with those reared on clover (Trifolium alexandrinum). Resorption bodies were significantly higher in the ovariols of females fed on L. termis and V.faba. Diet also affected longevity and body weight. Fecundity was highest in females reared on T. alexandrinum. Significant reduction in haemolymph protein was noted in females reared on L. termis and V. faba. Nitrile (allylcyanide) significantly reduced the approximate digestibility (AD), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD), inhibited nymphal growth, increased food consumption and decreased its assimilation. Feeding grasshoppers on T. alexandrinum treated with 125–250 μ mole/g resulted in various degrees of malformation and death.

Tick populations were monitored between October 1991 and September 1992 at monthly intervals on 10 Boran (Bos indicus) heifers at Didtuyura ranch, Yabelo district, Ethiopia. Twelve different tick species in four genera were identified from a total of 16 026 specimens collected. Of all the ticks collected, Rhipicephalus spp. constituted 84.7%, Amblyomma spp. 9.9%, Boophilus spp. 4.8% and Hyalomma spp. 0.24%. The ventral parts of cattle were found to be the most favoured feeding sites for most of the ticks collected. The size ranges of the standard ticks collected were 4–8 mm; 9–16 mm; 4–8 mm and 8–13 mm for R. pulchellus, A. variegatum, B. decoloratus and A. gemma, respectively, while their respective male to female sex ratios were 2:1; 3.2:1; 1:5.4 and 2.6:1. Packed cell volume (PCV) values of blood samples taken from 600 cattle were monitored monthly during the study period. There was a reduction in PCV during the dry season of the year but generally the values were within the normal range of 32–40%. The parasites causing anaplasmosis, babesiosis and theileriosis (T. mutans) were detected by microscopic examination of blood smears and serologically (ELISA) at seroprevalence rates of 94.68%, 77.19% and 30.9% respectively.