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.

The histopathological changes caused by Bacillus thuringiensis var. entomocidus HD-635 in the cotton bollworm, Heliothis armigera, have been investigated using electron microscopy. Death of the larvae due to infection was a gradual process involving a sequence of symptoms. Most of the histopathological changes that occurred on the fourth day after treatment with B. thuringiensis were mainly localized in the midgut, where the epithelium was greatly affected losing its integrity; the peritrophic membrane and microvilli were degenerated; and the musculosa was also affected. Other associated effects were observed in the integument, nerve ganglion, fat body cells, tracheoles and Malpighian tubules. In the integument, the exo- and endocuticles were clumped with an obvious separation from each other. An obvious degeneration of the nerve cells surrounding the second abdominal nerve ganglion as well as the neurilemma of the nerve fibres occurred. Vacuolization of the fat body cells, degeneration of their nuclei and destruction of the membraneous sheath surrounding these cells occurred. Tracheoles showed excessive cellular hypertrophy with disintegration of its mitochondria. The Malpighian tubules showed a reduction in their lumen, with nuclei degeneration and nuclear chromatin clumping. Uric acid crystals were released in the lumen of the tubules and a rupture was observed in some parts of the microvilli. A rapid phagocytosis occurred in the haemocytes. The plasmatocytes and granular haemocytes phagocytosed the bacteria. The counts of haemocytes were at a minimum and bacterial numbers at a maximum on the fourth day after feeding the larvae on B. thuringiensis-contaminated diet.

The biology of the sorghum shootfly, Atherigona soccata Rondani, was studied at the Corn and Sorghum Research Centre, Thailand. The preoviposition period is 3–5 days long. The females deposited a mean of 238 eggs with an average incubation period of 3 days. The larval development required an average of 7.8 days, and the pupal stage was 7.1 days long. The adults were reared with ordinary sugar, yeast and water. The females lived an average of 30 days and the males 20 days.

Carbofuran granular formulation is still the leading product for the control of the shootfly at the Research Centre. The application rate in the seed furrow is 0.45–0.60 kg a.i./ha with a row spacing of 75 cm. Furadan® 30ST, an emulsifiable formation of carbofuran, can also be used as a seed dressing at a rate of 20 cm3/kg of seeds. Counter®, another soil systematic insecticide, has been found effective in controlling the sorghum shootfly.

A modification of the ICRISAT trap for the sorghum shootfly is described. The trap may be effective in reducing the fly population.

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.

When males of Tribolium castaneum (Herbst) substerilized with 35, 40 or 50 Gy of gamma irradiation (I) were added to untreated (U) pairs of adults at I : U ratios of 1:1, 2:1 and 5:1, the percentage of hatched eggs was increased by increasing the dose administered to males, as not expected, at equal flooding ratio. The calculated degree of competitiveness showed that males irradiated with the lowest dose (35Gy) were more competitive than males irradiated with the highest dose (50 Gy). However, increasing the ratio of irradiated males with 50 Gy to 10 or 20 increased, accordingly, the competitiveness value. The results also indicate that if an equal number of irradiated males and females with 50 Gy, which had given 99.16 % sterility, were placed with untreated pairs of adults at different ratios (1:1, 5:1, 10:1, and 20:1), the effectiveness was more promising. Moreover, the data further suggest that the effectiveness was enhanced when the ratio of irradiated males and females was increased. Thus, the presence of sterile females along with sterile males in the stored products appears to dilute the effectiveness of normal males, which otherwise would mate with normal females.

The ability of three anti-juvenile hormone agents (AJHAs) to prevent the juvenile hormone dependent phase of larval-pupal transformation has been investigated. Neck-ligated post-feeding last instar larvae of Spodoptera mauritia were treated topically with different doses of a juvenile hormone analog (JHA) or the AJHAs, tetra-hydro-4-fluoromethyl-4-hydroxy-2H-pyran-2-one (FMev), ethyl-4-[2-(tert-butyl carbonyloxy)butoxy] benzoate (ETB) and ethyl-[E]-3-methyl-2-dodecanoate (EMD). Untreated ligated larvae or those treated with acetone survived for 12 ± 1 days without showing any sign of pupal cuticle secretion. On the other hand treatments of ligated larvae with different doses of JHA induced pupation. Among the three AJHAs tested treatments of ETB promoted pupation. Treatments of ligated larvae with lower doses of EMD induced the formation of larval-pupal intermediates whereas those treated with higher dose moulted into either pupae or larval-pupal intermediates. FMev-treated larvae exhibited a complete inhibition of moulting and metamorphosis. In order to study whether AJHAs would prevent the JHA induced pupation, neck-ligated larvae were treated simultaneously with different doses of AJHAs and 1 μg JHA. Co-application of JHA with different doses of EMD induced pupation in majority of the ligated larvae and thus appears to a certain extent to counteract the effects of treatments of same doses of EMD alone. Co-application of JHA with different doses of ETB elicited pupation in all the surviving ligated larvae. To a large extent co-application of JHA with different doses of FMev failed to induce pupation. The significance of the findings is discussed in the context of the mode of action of these AJHAs.

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.

Teneral nulliparous tsetse Glossina pallidipes were infected with virus-like particles by two pathways: haemocoelic microinjection, and oral feeding with a micropipette. Samples of tsetse were dissected every 3 days; and at 22 days post-infection, cumulative per cent infection was 44.4 and 31.3% for microinjection and per os infection, respectively. Natural virus-like particle infection in the population was 3.6%. Thus the infectious nature of virus-like particles was established, together with two possible pathways of infection.

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.

Electrophoretic studies of Guatemalan blackflies, Simulium ochraceum, the main vector of Central American onchocerciasis, were performed using isozyme patterns. A total of six larval and adult populations originating from four localities (a non-endemic area, Finca La Ruda, a low-endemic area, Finca Rincon, and two high-endemic areas, Finca Brote and Finca Recreo) were analyzed. The enzymes examined were adenylate kinase (AK), alkaline phosphatase (ALP), glucose phosphate isomerase (GPI), hexokinase (HK), isocitrate dehydrogenase (IDH), leucine aminopeptidase (LAP), malic enzyme (ME), and phosphoglucomutase (PGM). Of these, six enzymes, AK, ALP, HK, IDH, LAP, and ME showed no variation either within or among populations. GPI and PGM were found to be highly polymorphic in all of the six populations. χ2-test for fit to Hardy-Weinberg equilibrium (HWE) revealed that the distribution of the phenotypes of the two polymorphic enzymes was not significantly out of the HWE. A verages of values of proportion of polymorphic loci (P) and heterozygosity per individual (H) of the six populations were 0.234 and 0.084, respectively, each of which was similar to the values reported for different groups of organisms (Nei, 1975). Genetic diversity among populations was measured by FST and GST and both parameters showed that the non-endemic population from the Finca La Ruda (Dl) was greatly differentiated genetically from the other five populations. Estimates of genetic distance (Nei, 1975) showed that the Dl population was furthest from the other populations.

Laboratory reared populations of Spodoptera exempta (Wlk.) had higher net reproductive rate and capacity for increase on maize, Zea mais L. and star grass, Cynodon dactylon (L.) Pers. than on Kikuyu grass, Pennisetum clandestinum Chiov., Guinea grass, Panicum maximum Jacq. and Setaria plicatilis (Hochst.) Hack. These parameters were greatly influenced by the larval mortality, but in all cases they were greater than one demonstrating that S. exempta populations can multiply on all the host plants tested. Since no populations with stable age distributions are known for S. exempta the net reproductive rate is more appropriate than the capacity for increase in estimating its population growth.

The developmental, oviposition, and mortality rates for the polyphagous earwig Diaperasticus eryihrocephala Olivier feeding on pollen and Ephestia kuehniella Zeller eggs were measured at constant temperatures of 18, 25 and 32 °C. The developmental period for D. erythrocephala required 533 degree-days (DD) above a threshold of 6.7 °C. Egg and larval development rates increased with increasing temperature, with the shortest developmental period being recorded at 32 °C. However, egg and larval mortality and larval malformation rates were significantly higher at 32 than at 25 and 18 °C. Over a period of 60 days, females laid an average of 26.5 eggs at 25 °C and none at 18 °C. Based on the results obtained, it is concluded that of the three temperatures, 25 °C is the most suitable for the laboratory mass rearing of D. erythrocephala.

Results of research on biology of Thinophilus guineensis Coul. et Neg. (Diptera, Dolichopodidae) confirm the importance of predaceous feeding behaviour of some other species of Dolichopodidae such as Medetera fisch, Hydrophorus fallen, Sciapus fatten, Diaphorus meigen, etc. Larval mortality of some pests (mosquitoes, blackflies, scolytes, etc.) reach 83 to 99%.

These species, because of their extraodinary ubiquity and their biocoenotical importance, could well be used in biological control programmes of vectors of pathogens affecting man and other animals or pests in agroforestry.

A spreadsheet computer model of the benefits and costs of tsetse control has been developed. It aims to provide a sufficiently standardized framework for setting these out so that widely different situations can be compared. For this purpose, the main variables are grouped into four categories: cattle production system, disease impact on productivity, tsetse control costs and stocking density (represented by cattle in the area before control and those transferred into the area subsequently). The model covers direct benefit due to changes in productivity resulting from reduced mortality, morbidity and drug use and indirect benefits due to transfers of cattle into the area and the increased use of work oxen. A series of runs of the model based on a cattle production system oriented towards draught power production is used to illustrate how the model can be used to define the conditions under which tsetse control is likely to be economically viable.

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.

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.

Sexual receptivity was investigated in female Ghssina morsitans morsitans Westwood after mating. The degree of insemination and duration of copulation could affect sexual receptivity when females mate with immature males. However, matings with mature males showed no effect. The “jerking phase” appears to be an important mechanical factor in female post-mating refractory behaviour.

The dwarf variety of coconut, Cocos nucifera L. (Palmae), was found to be eaten by the larvae of the African armyworm, Spodoptera exempta (Wlk.). The comparison of the armyworm infestation on the leaves of the coconut seedlings and the adjacent grass species revealed lower larval density and growth rate on coconut seedlings. This observation suggests that a small population of the African armyworm can survive and develop on the leaves of the dwarf variety of coconut.

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.

Mobility of tsetse flies is influenced by various factors including the search for a blood-meal. Field observations on the feeding behaviour of tsetse are difficult. The use of bait animals for experimental purposes may indicate food sources but not host selection under natural conditions. Availability and density of a particular potential host species in a tsetse habitat can influence the feeding habit of the latter. Flies are capable of adapting to new host species in the absence of the usual ones. Host selection might be due principally to availability of host(s) and not based on true preference. Tsetse flies respond to visual stimuli from moving objects. Their shape, colour and size are important factors eliciting visual response. Whether these factors are distinguished separately or in combinations is not clear. Odour emanating from live hosts causes up-wind olfactory response towards the source(s), resulting in actual landing on test targets even when the hosts are out of sight. The components of odour have not been isolated. It is therefore doubtful if host selection can be associated with odour, as this might imply that tsetse can differentiate the odours of the different potential hosts. The difficulties in ascertaining true host selection by tsetse are discussed to stimulate further investigations.