Seasonal incidence of the sorghum earhead bug, Calocoris angustatus Lethierry, was studied by sowing the crop once in 10 days, throughout the year during 1978 and 1979, as well as by sowing it at fortnightly intervals from early “kharif” to late “rabi” during 1979. The bug was found throughout the year except for a few weeks during March, April and May. The milky stage of the earhead was the most preferred stage compared to pre-flowering, a third flowering, flowering and ripening stages. The adults dominated during pre-flowering and a third flowering stages whereas nymphs dominated during milky and ripening stages. The computed seasonal indices were higher during August (230), September (222), October (224) and January (215) which coincided with blooming and milky stage of sorghum in general fields. Correlation studies between the bug population at the milky stage and maximum temperature indicated negative and significant (r = -0.2967) relationship, and positive and significant (r = +0.2727) relationship with relative humidity. Low incidence of bugs was observed on the crop sown during June.

Simple models can be used to study the effects of factors involved in trypanosomiasis transmission, provided rough parameter estimates are available. The models should also be tested against field data; more complex models are needed whichrelate prevalence to the sensitivity of the diagnostic method, and take account of age-dependent changes in host susceptibility.

The pupal parasitoid Xanthopimpla stemmator Thunberg oviposits in the pupae of the spotted stalk borer (or sorghum stem borer) Chilo partellus (Swin). The adult parasitoid emerges from the pupal case, killing it in the process. Ten mated females of the parasitoid had an average longevity of 30 days (maximum 37 days and minimum 22 days). The number of progeny produced ranged from 71 to 115, with an average of 84.5. The male:female sex-ratio of their progeny averaged 1.14:1. The maximum mean progeny production per day (mx) was 1.9. The innate capacity for increase was 0.131 per female per day; and the population multiplied 43.43 times in the generation time of 28.78 days.

A study of the noxiousness of the African white rice stem borer, Maliarpha separatella Rag carried out under controlled field conditions has revealed that the impact of this pest on the yield and its components is assessable. For mean infestation rates up to 68% during the period of highest sensitivity of a paddy rice culture (second half of tillering to panicle initiation), no significant decrease could be observed in the number of panicles, nor any significant increase in the number of white heads and the number of empty grains per hill. However, with increasing infestation rates, the number of immature panicles increased and the number and weight of filled grains per hill decreased. An explorative analysis of the infestation rate-yield loss relationship, showed that a sigmoid model describes this interdependence appropriately. The proposed economic injury level (EIL), is here considered more the result of an approach, which had as its goal the re-definition of the status of the pest than as an instrument of a chemical control programme with treatments based on an action threshold.

The diel activity patter n of Glossina austeni was studied on the south coast of Kenya, and in the laboratory. In the field, flies were sampled hourly by continuous catch from a standing vehicle, or by traps. In the laboratory, observations were made of the flies' take-off-responses to host odour at various times of the diel cycle, in a flight chamber. The results showed that G. austeni is day-active with some activity throughut the daylight hours, but with significant peaks occurring at 09.00–10.00h and between 14.00 and 17.00h, i.e. a roughly V-shaped pattern.

The reasons for assessing crop losses due to pests of cereals are reviewed; for making decisions in pest management based on costs and benefits, for allocating resources on the most important pests, and as a guide to how yield is lost. Crop yield is seen as a balanced system, with inputs and output. The methods of quantifying pest attack, measuring losses and the difficulties met are discussed: the interaction of losses, interplot interference, mixed crops, loss distribution and crop compensation. Surveys of loss are described, with examples.

Mites are known to live in a diverse number of habitats, but only recently have they been collected in large quantities from the tropical canopies, where they have a diverse feeding habit.

We studied the canopy oribatid mites from five localities of Mexican oak species. Foggings with a natural pyrethrum in aqueous solution were employed to obtain the arthropods living on the canopy of the oaks. Specimens were taken from two collections made in February and August of 1997.

The total number of mites obtained with the two foggings was 5824 specimens. Most of them (95%) were collected during the rainy season and only about 5% during the dry season. The Mesostigmata were represented by 194 specimens, Prostigmata by 849 and the Cryptostigmata (or oribatids) were by far the most abundant, with a total of 4781 specimens. This group represents only 3% of total mite abundance during the dry season and 97% during the rainy season.

Quercus crassipes harboured more oribatid mites during the dry and rainy seasons, and the most important mites in abundance and frequency were Camisia sp., Phauloppia sp. and Scapheremaeus sp.

A millet farm was divided into five treatment plots of three replicates. The population of the grasshoppers was assessed by flushing and the percentage leaf damage on the millet was estimated by visual grading of the defoliated area. Weeding discouraged oviposition and reduced the vegetative shelter and the population of the grasshoppers. The unweeded plots had high levels of defoliation and low grain yield of millet relative to the weeded plots. Oedaleus spp were the most numerous grasshoppers and probably caused the greatest damage on pearl millet. The common weeds on the farm were Brachiaria xantholeuca, Cenchrus biflorus, Ipomoea vagans and Mitracarpus scaber.

Eggs and larvae of the bollworms Earias spp. followed a uniform distribution on G 27, LD 133, LD 230 (Arboreum) and F 414 (hirsutum) cotton varieties in Ludhiana (Punjab). Clump distribution of Earias eggs and larvae on the four cotton varieties may result from environmental heterogeneity. Although Earias gravid females laid maximum eggs at the top (41–50 cm) plant canopy mostly, examination of the whole length of the plants is suggested for sampling Earias on the four varieties.

Sample sizes of 10 plants in arboreum and seven in the hirsutum variety resulted in reliable estimates of population at 5% risk level. Injured fruiting bodies and larval numbers were significantly and positively correlated.

The eggshell fine structure of a lepidopteran pest of mulberry, Amata passalis F. (Lepidoptera: Amatidae), was investigated using scanning electron microscopy. The micropylar rosette around the micropyle, shell imprints, aeropyles and regional differentiation were studied. The surface of the amatid eggshell had a highly decorated chorion with structural difference at the anterior and posterior poles. The micropylar structure was at the anterior pole of the spherical eggs (488 ± 0.595 mm in diameter), opposite to its side of attachment to the substratum. The micropylar rosette measured 51.20 ± 0.52 mm in diameter and was formed of 15–19 petal-shaped primary cells. The micropylar opening into the micropylar canal was 3.76 ± 0.52 mm in diameter. The entire surface of the chorion had a reticulate pattern of pentagonal and hexagonal cells, each of which was boarded by 3 to 6 aeropyles of similar size (0.36 ± 0.008 mm in diameter).

The effects of climate on the diurnal biting pattern of Simulium damnosum s.s. were measured at Jos Plateau, Nigeria. Rain in the hours prior to the catch inhibited morning activity by lowering the temperature and light intensity, and raising the humidity. Under shade there were no remarkable fluctuations in the light intensity, and no obvious peaks in activity; in sunny places, activity was bimodal, with a small morning peak and a pronounced afternoon one. The fastest changing climatic factor relative to an increase in the biting activity of flies was light intensity; followed by temperature.

The leucaena psyllid, Heteropsylla cubana, was studied under constant temperatures ranging from 21.5 to 35.0°C. Total mean development time was 11.2, 9.6 and 8.1 days at 21.5, 25.0 and 30.0°C respectively. For these temperatures, the mean number of eggs laid was 532.3, 758.3 and 374.7 with hatch rates of over 90%. At 35.0°C, a mean of only 4.5 eggs/female were laid in 24 h, egg hatch (9.0%) was very low and nymphs did not complete their development. Nymphal survival was only 65% at 30.0°C, compared to 84.2 and 87.6% at 21.5 and 25.5°C, respectively. Adult longevity was highest at 25.0°C; females outlived males at all temperatures. Age-specific life table statistics are given for the three temperatures. The calculated intrinsic rates of natural increase (rm) at 21.5, 25.0 and 30.0°C were 0.226, 0.293 and 0.324 respectively. Relative humidities in the range of 25 to 84% did not affect egg hatching, nymphal survival, or adult emergence of H. cubana.

The life cycle and development of Zonocerus variegatus (variegated grasshopper) from southern Benin was studied at the International Institute of Tropical Agriculture (IITA) Benin Station, from March 1992 to August 1994. Hoppers of the 1st to the 5th stage were collected from uncultivated fields in the Atlantic Province and placed in cages and their development evaluated by counting the number of insects in each stage every two days until the adult stage. Mating and the number of egg pods were also recorded. The study showed that Z. variegatus has only one generation in southern Benin, running from September/October to July/August. Hatching occurs between September/ October and February/March. Zonocerus variegatus females can oviposit up to five times and the interval between ovipositions varies from 14 to 32 days. The variegated grasshopper has an egg diapause and egg hatching is not synchronised. These observations explain the almost perennial presence of the variegated grasshopper in southern Benin.

A tsetse-control trial was carried out in a primary forest habitat on Unguja Island of Zanzibar to assess the effect of insecticide-impregnated blue cotton screens on a population of Glossina austeni Newstead. In November 1991, screens were deployed at densities of 45–70 per km2 and the fly population was monitored monthly using sticky panels. Both female and male daily catches were not affected during the initial five months after screen deployment, but the physiological age distribution of female flies shifted significantly towards younger groups. Females were more influenced by the screens than males. The fly population was very low after the long rainy season, but increased to pre-control levels three months after the flooding of the forest floor. Thereafter, male and female apparent densities decreased, and 78–91% and 98–99% suppression was obtained for males and females respectively at the end of the 18-month intervention period. While effective control of G. austeni using blue cotton screens was shown to be feasible, it required a high deployment density and a long intervention period.

The effects of gamma irradiation from a 60Co-source on Glossina palpalis palpalis (Robineau-Desvoidy) were established in laboratory tests. Dose-response data indicated that fecundity was reduced by about 95% following exposure of late stage puparia or young adults to 11–13 krad in air and 15–18 krad in a nitrogen atmosphere. None of the treatments had a detectable influence on the viability, mating behaviour, inseminating capability or competitiveness of the adult males.

When irradiated males were combined in varying ratios with untreated males and females, increasing numbers of sterile males resulted in a considerable reduction in pregnancy stages beyond the egg stage, an increasing proportion of parous females with an empty uterus due to expulsion of a dead embryo after embryonic arrest or due to ovary blockage and an increasing percentage of females with a degenerating egg in utero.

Remating of inseminated females with fertile males during the period when most of them had emptied their uterus (day 14–20) after embryonic arrest, had no noticeable effect on the sterility rate.

A most important consequence of recurring embryonic death was a detectable imbalance between intra-uterine and ovarian development. Some aberrations can be used as additional criteria for monitoring the effectiveness of sterile males released in the field.

Females irradiated in the pupal or adult stage displayed a normal receptivity and insemination rate and survived distinctly longer than untreated controls. Moreover, they built up abnormally abundant fat bodies and showed multiple mating scars (restricted to the palpalis group species) and completely atrophied ovaries.

It is postulated that the release-recapture and examination of the reproductive tract of irradiated females during an advanced stage of sterile release vector control operations would give evidence of mating that could expose the existence of relic wild populations, particularly when the natural tsetse population has been reduced to, levels below the threshold detectable by conventional techniques.

This paper discusses insect behaviour and host plant resistance under single-plant species resistance and plant population resistance. Under single-plant species resistance, the effects of repellents, surface texture, shape and colour to insect behaviour are briefly reviewed and discussed. The effects of plant species diversity and plant density on insect behaviour are discussed under plant population resistance. Where possible, this discussion is illustrated with examples from recent behavioural studies on the weevil, Sitona lineatus L.

Nauclea diderrichii (De Wild and Th. Dür.) (common name Kusia and trade name, Opepe) is an evergreen tree found throughout the tropical rainforests of West Africa. It is heavily exploited for its timber and listed as vulnerable on the IUCN Red List of Threatened Species. The shoot borer Orygmophora mediofoveata Hamps, which attacks the nursery stage, has hampered attempts to establish N. diderrichii plantations in Ghana. This study examined the potential of four insecticides to protect N. diderrichii seedlings from O. mediofoveata attack and damage. Four insecticides–Pyrinex (chlorpyrifos), Dursban (chlorpyrifos), Cerox (dimethoate) and Golan (acetamiprid)–were applied to four-month-old N. diderrichii seedlings growing in full sunlight and under shade (80% of normal light), to evaluate their effects on incidence of attack, survival, severity of damage and growth. Insecticide treatment and light conditions had variable effects on the damage and growth of the seedlings after six months of evaluation. Seedling survival was not significantly influenced by the insecticide treatment. Percent survival of insecticide-treated seedlings did not differ significantly from that of control seedlings in full sun; however, under shade survival of treated seedlings was significantly higher than control seedlings. Nonetheless, control seedlings in full sun had higher survival (92.5%) than those under shade (62.5%). Insecticide-treated seedlings in full sun had lower incidence of shoot borer attack than those under shade. In full sun, dieback incidence following shoot borer attack was significantly lower for insecticide-treated than control seedlings. Growth in height and girth of seedlings was influenced positively by both insecticide and light, with girth especially being significantly lower under shade conditions. Currently, N. diderrichii seedlings are typically raised under shade; however, this study shows that raising seedlings in full sun with insecticide application could result in faster and better growth.

The colony foundation and development, and pattern of young and established nests of Odontotermes obesus and O. wallonensis were investigated. Swarming of alates of both the species occurred during pre-monsoon (April/May) and continued throughout the wet months. After pairing, alates of both the species selected sites in crevices of the soil or in loose soil for the foundation of a colony. The active construction of the mound was observed during the cool hours of the day in rainy months.

The young nests of O. obesus was conical-shaped with one or more conical turrets, whereas it was dome-shaped with one or two domes like turrets in O. wallonensis. In young colonies, the fungus combs were aggregated in the central cavity and the royal chamber was situated beneath usually at the centre. The established nests of both the species were extended by addition of vaults, galleries, runways, etc. The mound nest was extended in vertical direction in O. obesus, whereas it was extended horizontally in O. wallonensis.

Twenty-one insecticides were tested for acute toxicity by surface film contact method against the grasshopper, Zonocerus variegatus (L.) in the laboratory. Decamethrin, cypermethrin, lindane o, o-diethyl(p-methyl sulfinyl) p′-phosphorothioate, and dieldrin were highly potent. Moderately potent insecticides were propoxur, bioallethrin, telodrin, isodrin, heptachlor and rotenone. A toxic symptom common to all potent insecticides in the female was the opening and closing of ovipositor valves which remained wide open at death. Five insecticides—dieldrin, telodrin, p, p′-DDT, chlorobenzilate, DMC and chlordimeform induced cannibalism among the treated females.

Mating and oviposition of Earias vittella was studied in the absence or presence of the host (okra fruit) or the host odour. When the host was accessible, there was a significant increase in the frequency of copulation, the number of spermatophores transferred and the number of eggs oviposited. Availability of host odour, instead of the host, gave similar results. Further, in general, the number of eggs oviposited by a female was significantly correlated with its mating frequency.