Larvae of the Caribbean fruit fly, Anastrepha suspensa Loew (Diptera: Tephritidae) parasitized by the wasp, Biosteres longicaudatus Ashmead (Hymenoptera: Braconidae), were topically treated with diflubenzuron (Dimilin®), a chitin synthesis inhibitor, at 100, 500 and 1000 ppm. Each dosage was initiated during the parasite's egg stage, each of four larval stages and the pupal stage (pharate pupa + pharate adult). Adults emerging from all immature stages treated with the two higher dosages were significantly (P < 0.05) fewer than the controls. Developmental stages, in decreasing order of susceptibility to diflubenzuron were: egg, first instar, pharate adult, pharate pupa and larval stages two to four. Abnormally developed ovipositors occurred in some adults which emerged from eggs, pharate pupa and pharate adults that were treated with the two higher concentrations. Such females were unable to successfully locate and parasitize hosts. Females with normal ovipositors which emerged from treated eggs and pharate adults were able to find and attack hosts but had significantly fewer eggs in their ovaries and oviposited less than the controls. The F1 eggs laid by these females developed normally and survived to adulthood with no apparent abnormalities.

The behavioural process by which a mosquito finds a potential host organism is mediated by olfactory receptors on the insect's antennae. Lactic acid (LA) is a host-related odour common to all potential hosts. On the antennae of the female are two LA-sensitive neurons; one of these is excited by LA but the other is inhibited by LA. Furthermore, the sensitivity of the LA-excited neuron is correlated 1:1 with the presence of host-seeking behaviour such that when host-seeking behaviour is inhibited following a blood meal, the sensitivity of the LA-excited neuron is markedly decreased. The inhibition of host-seeking behaviour and the decrease in LA-sensitivity are induced by a hemolymph-borne factor released during oocyte maturation. The source of this factor is the fat body of blood-fed females, which requires a vitellogenic ovary for its production and/or release. The combined activity of the two types of LA-sensitive neurons together with the shift in sensitivity of the LA-excited neuron from a range where host levels of LA are present to a range exceeding LA levels expected from a host are sufficient to account for the inhibition of host-seeking behaviour following a blood meal.

The phytochemical ptumbagin, isolated from Plumbago zeylanica L., was applied in 2 and 5 μl doses of 0.1% concentration on the surface of Dysdercus koenigii F. adults and its effect on the haemocytes of the bug, studied by transmission electron microscopy. All the five haemocyte types viz. the prohaemocyte, plasmatocyte, granular haemocyte, oenocytoid, and the adipohaemocyte are affected within a period of 24–48 hr. The effect begins with an acute state of vacuolization of the cells and a gradual destruction of the organelles, followed by dissolution of the plasma membrane and passing out of the internal organelles, like the mitochondria and the endoplasmic reticulum. This phenomenon is responsible for a consistent elimination of the haemocytes from the blood, leading to lowering of the resistance and mortality of the insects.

Epidinocarsis lopezi proved to be an efficient biological control agent of the cassava mealybug (CM), Phenacoccus manihoti, despite apparently low parasitization rates. Laboratory experiments indicated that its killing power at higher temperatures was two to three times higher than the per cent mummy formation suggested. Following an attack by an E. lopezi female some CM hosts were killed through host feeding and some through successful development of the parasitoid larva, processes which both benefit the parasitoid. If the host was found unsuitable, no egg was laid, and the CM survived the attack. Other CM died from the wasp attack without forming a mummy. This mortality is attributed to mutilation and unsuccessful larval development of E. lopezi. Most ovipositions induced a defence reaction by the host that lead to melanization. This process involved mainly wound tissue, sometimes partial encapsulation of the tail end of the parasitoid larva, and infrequently complete and fatal encapsulation of the parasitoid larva.

Simple methods for production of all life stages of the banana weevil on its natural diet, banana rhizome and pseudostem are presented. Their effectiveness, labour demands and applicability for different purposes are discussed. The most effective method for the production of eggs, pupae and adults is the utilization of the rhizome part of suckers, whereas larvae are easier to recover from pseudostem. The hatchability of the eggs produced is high.

The relationship between seasonal numbers of outbreaks of African armyworm (Spodoptera exempta) in Kenya and Tanzania, and early season rainfall in source areas has been examined using records for 21 seasons. Significant inverse relationships were found between numbers of Kenya outbreaks and early season rains in the Kisumu area, and between numbers of Tanzania outbreaks and early season rains in the Morogoro and Mtwara areas. Total Kenya and Tanzania outbreak numbers were significantly inversely related to early season rainfall for 8 areas combined. These results suggest that early season rainfall totals, either from specific likely source areas or countrywide, could be used in January to give a seasonal forecast of likely numbers of armyworm outbreaks during the rest of the season. Seasons with more than average numbers of outbreaks often follow poor early season rains and visa versa. Further work is needed to establish biological causes of this apparent relationship.

Effect of fluctuating and constant temperatures on different population growth parameters of Chilo partellus (Swinhoe) infesting sorghum was studied in the laboratory. On the basis of intrinsic rate of natural increase (rm) values, the optimum constant and fluctuating temperatures for the multiplication of this pest was 30 ± 1°C and 31.0 to 35.8°C, respectively. But the favourable range of temperature varied from 27.5 to 30.0°C under both constant and fluctuating temperature conditions. Mean length of generation (T) at this range of temperature varied from 38 to 41 days. It seems that Chilo partellus may not persist at or above 40°C and below 20°C, as the rm values at these temperatures were negligible or zero. This information can be used in working out the strategy for controlling Chilo partellus.

The use of fish meal and detergent water has been shown to be simple, economic and reliable for sampling of shootfly populations. Various mixtures of fish meal with other ingredients were evaluated. The most potent mixture was fish meal-yeast-ammonium sulphide, but generally fish meal alone was adequate and the most readily available attractant. The attractance of fish meal was found to be related to its degradation; it increased from the first to the third or fourth day, and then decreased. The chemicals responsible for the attractance of fish meal have yet to be identified, but in all probability they may be the amines resulting from biodegradation of the meal.

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.

Lepidopteran stem borers account for heavy losses in cereals in areas where they are prevalent throughout Africa. Microsporidia, especially Nosema sp. may be developed for use in the management of this group of insect pests. Studies carried out so far show that the application of Nosema spores may increase yield up to 34% in sorghum when the plants are infested with Chilo partellus eggs and sprayed with the pathogen, and up to 80% in sorghum infested with borer larvae.

The procedure for spore production is simple, and may easily be adapted for small scale industrial production by local or regional communities and organizations. In trials aimed at the mass production of Nosema sp. for the management of C. partellus, a yield of 109 spores/larva has been attained. If this production level can be maintained, then a system that produces only 6000 larvae/day would yield enough cadavers for preparation of 6000 1 daily. At the rate in which the pathogen suspension is applied as foliar sprays in the field, this would be sufficient to treat 5373 ha. If widely adopted, use of microsporidia would revolutionize cereal stem borer management in the tropics.

A high level of resistance to chlorpyrifos has been detected in Culex quinquefasciatus larvae from Dar es Salaam. To study the impact of this resistance on the routine anti-larval spraying programme with this chemical, pit latrines, cess pits and soakage pits were examined regularly after spraying. Larvae were eliminated immediately after spraying, but in most cases they re-appeared about 2 weeks later. Bio-assays with susceptible and resistant larvae in water samples from the pits showed that in most cases there would have been sufficient insecticide residue for at least 10 weeks to kill a susceptible population, but resistant larvae could survive in the water from about 2 weeks after spraying. Chemical analysis showed that the water was toxic to resistant larvae so long as it contained about 0.02 mg/l chlorpyrifos. These observations might have suggested that the routine spraying programme every 10 weeks would be having very little impact on the population now that resistance has evolved. However, in fact, adult densities in houses in a year with spraying on schedule were much less than in years when many sprayings were missed owing to shortage of supplies. Thus the regular spraying programme still apppears to have a beneficial effect.

A total of 2256 germplasm accessions, 3000 advanced generation breeding lines and 150 released varieties of rice were screened under artificial infestation in the greenhouse. Among these, 15 new germplasm accessions, 50 breeding lines derived from 16 crosses and 15 released varieties were resistant. Antibiosis was the predominant resistance mechanism; antixenosis affecting oviposition was noted in 33 resistant varieties. Biochemical composition of a set of resistant varieties along with susceptible checks, revealed that nitrogen content of seven test varieties was significantly higher than that of the susceptible checks, while in other six varieties it was lower than the checks. Similarly, eight of the resistant varieties had considerably higher percentage of polyphenolic compounds in basal stem portion, but seven other cultivars showed significantly lower concentration as compared to susceptible checks. Thus, it was apparent that there was no clear trend among the resistant cultivars as a group in relation to quantitative differences of chemical components analysed.

The use of incompatible males (IM) of (A) mating type to suppress the Iraqi (B) strain of Ephestia cautella, when the release ratio was 80:1:1 (A males: B males: B females, respectively), brought about a highly successful protection of uncovered loose dates against infestation with (B) strain in a simulated date store. Surprisingly the protection effect of IMs lasted for 230 days which commercially covers almost the whole period of date storage.

Since strain A males are believed to compete poorly against wild strain B males, the competitiveness of F1 males was measured in order to determine if they might be promising candidates for subsequent trials of the control of E. cautella by the release of incompatible males.

Urticating spicules of Hylesia moth of Guyana (H. metabus Cramer = H. urticans Floch et Abonnenc) are produced by trichogen and tormogen cells which form a monolayer hypoderm similar to that which produces scales. Urticating spicules are interpreted as modified scales.

The development and morphometrics of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) were studied on cassava and a description was made of the different nymphal instars and oter biological characteristics. The nymphal instars were distinguished using easily recognisable morphological characteristics. Abnormally developing individuals were also easily recognised. Regression analysis was highly significant between the length and width of nymphal instars modelled collectively indicating two-dimensional growth at least across three nymphal stadia. Males were smaller than females on the basis of body length, wing width and width of the abdomen. The insects showed better development on a Colombian cassava variety as compared to an African variety, Ebwanateraka from Uganda, and consistently showed a higher proportion of males than females (2.33: 1) for early-emerging individuals. Mean developmental period on both varieties was 22 days and the first instars accounted for the major part of the developmental period which ranged from 19 to 29 days. The mean number of eggs/female/day was 4.89. The actual events of first instar eclosion, which can last up to approximately five minutes, were described. The intervals of honeydew flow to the vasiform orifice lasted a minimum mean time of 20.8 seconds and a maximum mean time of 123 seconds.

A water–oil based pheromone trap was used to monitor seasonal population changes of Coniesta ignefusalis Hampson in millet-based cropping systems at Samaru, Zaria, Nigeria for three consecutive seasons (1997, 1998 and 1999). Daily meteorological data were obtained from the Meteorological Unit of the Institute for Agricultural Research, Samaru, Zaria, for the monitoring period. Two population peaks were observed in early August and September in 1997 and 1998. The first population peak in August 1997 was earlier and bigger than the one in 1998. A delayed emergence of the insects was observed in 1999 when only one population peak occurred and this was smaller than those in 1997 and 1998. Using step-wise multiple regression analyses, the relationship between pheromone trap catches of male moths and weather factors was assessed separately for each year to determine which of the weather factors contributed most to the insect population changes. Solar radiation in the preceding 10 days and minimum air temperature in the preceding 40 and 50 days explained 84.9% of the variance in population changes and flight activity of male moths in 1997. Wind direction and speed in the preceding 20 and 60 days respectively accounted for 80.6% of the variance in 1998, while maximum air temperature and relative humidity in the preceding 40 and 20 days respectively explained 99.9% of the variance in 1999. The functional regression equations developed involving these weather factors adequately predicted the changes in each year.

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.

Field experiments were conducted to investigate the attractiveness of fish bones to predatory ants in a maize agroecosystem. The fish bones were applied crushed in shallow furrows together with dry maize stalks, or broadcast on the soil surface at 3 application rates: 0, 40 and 80 kg/ha; subsequent reduction in termite attack on maize plants was then assessed. Burying the fish bone powder caused higher ant nesting (10–78 %) than surface broadcasting (12–39 %). Attractiveness of the fish bones and the predatory efficiency of the ants against termites in maize was also highest with a dose of 80 kg/ha (1.0 kg/plot) causing higher nesting of ants (>90 %) and 54 % lower termite damage to maize plants compared to control plots. Dose responses indicated significant relationships between amount of fish bone powder applied and termite activity and also between termite damage and maize yield. The mechanism by which the ants are able to protect maize against termite damage may be twofold: direct kill as a result of their predatory action and termite avoidance of maize plants with ant nests. Further studies are required to assess the potential benefits of an integrated use of this technique with other non-chemical options for termite control in maize, such as intercropping.