Fourth instar larvae of laboratory-reared, Ctenocephalides felts and Xenopsylla. brasiliensis were exposed to 50% neem seed kernel extract (NSKE) for periods varying from 30 min to 24 hr. Mortality of larvae was observed from exposure periods of 2 hr and above in both species. At 24 hr exposure, 95.3% and 94.7% of C.felis and X. brasiliensis respectively were killed. LT50s were approximately 6 and 10.5 hr for C.felis and X. brasiliensis respectively. It was generally concluded that neem seed kernel extract was potentially larvicidal against the two flea species and that it could be effectively used for controlling the insects by properly dusting the latter's breeding sites with appropriate concentrations of the extract.

Deltamethrin (IR, 3R)-3(2,2-dibromovinyl)-2, 2-dimethylcyclopropane carboxylate of (S)-alpha-cyano-3-phenoxy-benzyl, was observed in the field in Zambia to offer a better residual effect against adult Rhipicephalus appendiculatus of up to 7 days post-treatment during a high infestation pressure period than on organophosphorus (OP) acaricide. A group of 20 cattle sprayed with deltamethrin wash of approximately 0.005 w/v at 14 days intervals carried an average of less than 12 ticks per head by the 7th day post-treatment, whereas two groups of 20 cattle each, dipped weekly in an OP at 0.05% w/v had an average of over 60 ticks per head. In a theileriosis infected area 14 days' treatment with deltamethrin would probably be unsuitable for disease control during high infestation period, but 7–10 days would probably yield better results than those likely to be obtained with OPs.

The larvae of Mussidia nigrivenella Ragonot, attack various fruits; it is the main maize cob borer in Ivory Coast. The development of attack during the cultivation, the behaviour of larvae in the field, the spatial distribution of eggs and larvae, the mortality of pre-imaginal instars and the annual fluctuations of populations are considered in this paper. This insect may represent an economical problem for seed producers in the south of the savannah area of Ivory Coast where its density exceeded 14 insects per cob, at harvest in 1984, whereas the risk of cob damaging by Mussidia nigrivenella appears to be very weak in the north and west of this region.

An experiment to examine the effects of different plant spacings on cowpea insect numbers and yields was undertaken at two sites in Nigeria. Two varieties, viz. Tvx 3236 and IT84E-1-108 were planted under field conditions at three different plant spacings. Plant spacing did not affect the number of Ootheca beetles, pod-borers, flower thrips and pod sucking bugs. Yield differences were not significant for the spacing regimes and there were no interactions between spacings and insect numbers for yields. Thus, plant spacing may not be an important control tactic in the management of the key cowpea insect pests in Nigeria.

Intensive investigations of genetic variation within and among populations of the whitefly, Bemisia tabaci, are under way in Israel and in Colombia. A polymorphic esterase (EST), which seems to be controlled by a Mendelian locus, has two alleles in sufficiently high frequencies to be useful as a genetic marker. The analysis of more than 10,000 individual adult whiteflies shows genetic differences among localities in the frequencies of the fast (F) and slow (S) alleles. These differences seem to be related to the intensity of insecticide use against the whitefly. The frequency of F is high in unsprayed areas and in control laboratory populations, but is close to zero in heavily-sprayed agricultural areas. The frequency of Fon cotton in agricultural areas is high in winter and spring, but decreases dramatically in the summer (coincidental with the onset of pest-control activities on cotton). A similar temporal pattern on untreated Lantana may be due to migration of adults from agricultural fields. There was no indication of differentiation of populations on different host plants. In Colombia, the difference in EST patterns in different States are very pronounced, suggestive of geographical races. Small samples from Florida, California and Kenya indicate that B. tabaci in different countries may be genetically distinct.

Several tsetse control campaigns have been carried out in Senegal. During the 1970s a ground spraying campaign was carried out in the Niayes region (relic of Guinean forest infested with Glossina palpalis gambiensis, Vanderplank, 1949). At the beginning of the 1980s, the chemical control was strengthened by use of screens and biconical traps. As a result no fly has been caught in the region since 1983.

An assessment of the second method, done in Kolda (south of the country), has shown a reduction rate of 98% against G. palpalis gambiensis.

The elegant grasshopper, Zonocerus elegans Thunberg, occurs in large numbers in Kilosa district during the dry season June to January and attacks a wide range of wild and crop plants. Its impact as a pest of crop plants becomes more noticeable from the middle of the dry season when the hoppers are well advanced and the only alternative food available are vegetables in backyard gardens and river valleys. The grasshopper damage continues throughout the vuli (short) rains until the end of the oviposition period in January, thus limiting the production of green vegetables in the district. A study on the biology and ecology of the pest in Kilosa district with emphasis on short term control strategies was started in 1987. Spot spraying with insecticides to kill the early instars was found to be effective, but area-wide implementation was necessary to prevent re-invasion of cleared areas.

Scanning electron microscope (SEM) micrographs of aedeagi and pygofer processes of some Cicadulina spp. are presented for the first time. They should assist in the identification of Cicadulina spp. by entomologists who are not trained in taxonomy, and who work in national research programmes in Africa without access to well-equipped libraries and reprint collections, that offer ready access to the original descriptions of Cicadulina spp. A number of national maize research programmes recently initiated studies on Cicadulina leafhopper biology, behaviour, ecology and mass rearing for resistance screening to streak virus and all of them face the problem of species identification. This report summarizes widely scattered publications and provides new illustrative information to assist in the identification of Cicadulina spp. by national scientists in Africa.

Entomopathogens have been isolated and developed for the control of various lepidopteran, coleopteran, dipteran, hymenopteran, homopteran, and even acarine pests. Among the orthopteran pests, the acridid defoliators are important in Africa, and the periodic outbreaks of the desert locust, Schistocerca gregaria; red locust, Nomadacris septemfasciata;migratory locust, Locusta migratoria migratorioides and brown locust, Locustana pardalina; as well as numerous grasshoppers, cause extensive crop losses. Laboratory and field tests carried out on control of locusts and grasshoppers using microorganisms have shown that there are key candidates which could be used for the management of these acridid pests.

Regular field surveys were carried out in 2 week intervals in 1986 and 1987 to determine population density, species composition, migration activity of Cicadulina leafhoppers and their infectivity with maize streak virus (MSV) in different ecological locations of southeastern Nigeria: mangrove swamp forest (IITA and RIART station at Onne), deltaic swamp forest (RSUST, Port Harcourt), seasonal swamp forest (Iriebe) and high forest zone (NCRI, Amakama near Umuahia).

Population density was always low during dry season, significantly lower in the rain forest zone and higher in the swamp forest, rapidly rising in the second rainy season in all ecological zones and reaching its maximum before the rains finally stopped. Sharp increase in the population density in Nov. and Dec. may indicate mass migration activity of Cicadulina leafhoppers from already dry areas of adjacent Guinea savanna at that period.

Six species of Cicadulina were collected from most of sampled areas. C. ghaurii was the predominant species in 1986 and 1987, averaging 55.9% for all locations and periods. Its portion was higher in the mangrove swamp forest (Onne) than in the high forest zone (Amakama). The predominance of other species declined in the order: C. triangula (18.2%), C. mbila (17.2%), C. arachidis (5.9%), C. similis (2.8%) and C. hartmansi (0.1%). In absolute values, the portion of individuals out of the total number of leafhoppers collected was for C. triangula 53.7%, C. ghaurii 25.5%, C. mbila 17.3%, C. arachidis 2.3%, C. similis 1.1% and C. hartmansi0.1%. A high population of C. triangula occurred only in the relatively short period in Nov.-Dec, especially in Iriebe and was correlated with the rapid increase of Cicadulina densities in all sampled areas; a high migration activity of C. triangula and C. mbila was confirmed.

Incidence of MSV in the surveyed farmers' field varied between 0–22% in the first rainy season (1987) and 12–25% in the second rainy season (1986). The portion of Cicadulina adults already infected with MSV under field conditions and capable of transmitting MSV to the susceptible maize seedlings varied from 3.3 to 23.3%, with higher values for leafhoppers collected at the end of the second rainy season.

By means of the GM (1, 1) modelling of grey system theory, the authors built the predicting models of Tryporyza incertulas (Walk) occurrence tendency with a computer, based on the insect pests occurrence data accumulated for 26 years from Feng Cheng county:

model I x(t + 1) = 71.2131e0.1136t - 68.2131

model II x(t + 1) = 58.2206e0.1254t - 55.2206

Tests indicated that the two models are valid, and if we use the models to predict the damage by Tryporyza incertulas in the year in which the damage by Tryporyza incertulas is serious, the results would contribute to the control of borers in the area in practice.

The economic injury level (EIL) of the maize stem borer, Chilo partellus (Swinhoe) was determined by artificially infesting maize (cv. Katumani) plants at three different growth stages; viz, 20, 40 and 60 days old plants with varying densities of newly hatched larvae; viz, 2, 4, 6, 8, 10 and 12 per plant constituting the borer population. The grain yield data obtained from the infested and the protected plants showed that maximum yield reduction and stalk damage occurred to the 20-day old crop, while there was insignificant larval effect on yields for the 60-day old crop. Regression analyses gave a significant linear equation (y = a + bx) which estimated the yields per plant at different infestation levels and these were used to calculate the economic injury level at each stage. The resultant EIL was 3.2 and 3.9 larvae/plant for 20- and 40-day old plants, respectively.

The banding patterns of six soluble enzymes of a Sogatella furcifera Horvath population from Sri Lanka, maintained in glass-houses on rice variety TN 1 at University of Wales, Cardiff, were studied. Crude homogenates of macropterous adults of both sexes were analysed, using polyacrylamide electrophoresis. The following enzymes showed activity and were stained: esterase (EST), lactate dehydrogenase (LDH), phosphoglucomutase (PGM), hexokinase (HK), glucose-6-phosphate dehydrogenase (G-6-PDH) and malic enzyme (ME). Number and relative mobility of bands varied between enzyme systems.