Host-plant resistance plays an important role in the insect-pest management either alone or in combination with other control methods. A number of sorghum genotypes showing varying levels of resistance to spotted stem borer, Chilo partellus Swinhoe have been identified using natural and artificial infestations. Major resistance mechanisms are antibiosis and tolerance, though some genotypes exhibit ovipositional non-preferences. There have been a number of factors involved in spotted stem borer resistance; a resistant genotype possesses either one or a combination of these traits. Progress has been made in developing borer resistant breeding lines with moderate yield and acceptable grain quality. Borer resistance is a quantitatively inherited trait governed by additive and non-additive genes. Epistatic gene effects are more pronounced under artificial borer infestation. Cytoplasmic effects appear to be present.

Studies on seasonal patterns of okra leafhopper, Amrasca biguttula biguttula Ishida were conducted for two years. Time series analyses were adopted for working out weekly seasonal index of okra leafhopper. Low incidence of leafhopper was recorded from June to mid-January. Results further revealed that incidence of leafhopper was highly correlated with minimum temperature. There was no discernible time lag for population increase of leafhoppers. Prediction of leafhoppers at different crop growth stages for various months of sowing was done using dummy variable technique.

Females of Bruchidius atrolineatus (Pic) lay their eggs in the fields on maturing or dry pods of their host plant, Vigna unguiculata. Under experimental conditions in the presence of maturing and dry pods connected with the plant, 80% of eggs are laid on maturing pods. The preference for maturing pods is observed in two generations of B. atrolineatus and varies with the age of females. In the presence of pods separated from the plant, 69% of eggs are laid on dry pods. These results show the importance of methodology during insect behavioural studies. In the absence of choice, reproduction of B. atrolineatus females is more stimulated with dry pods than with maturing ones. These experiments show that factors which influence the choice of the pods are probably different from those stimulating oviposition.

Laboratory and field methodologies for screening for resistance against Chilo partellus on sorghum and maize are reviewed in relation to the insect biology, plant phenology and insect-plant interaction. The value of field and laboratory techniques in achieving the goal to produce resistance varieties and hybrids is discussed. Recommendations for future work are made.

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.

In Acanthoscelides obtectus (Say) (Coleoptera, Bruchidae) several first instar larvae can use a hole made in the seed coat by a conspecific to enter the seed. The present study tests whether there exists different seed-coat piercing abilities related to the hatching rank. The hatching rhythm was found to be well synchronized with the periodic conditions. The hatching rank had no influence on the piercing behaviour. On the basis of these observations the hypothesis of a behavioural dimorphism as has been suggested in the literature may be rejected.

Hypoaspis solimani n. sp. was collected from compost from the farm of the Faculty of Agriculture, Cairo University, Giza, Egypt. Morphological characters of the different stages are described, illustrated and a key to the Egyptian species of Hypoaspis presented. H. solimani sp. n. was successfully reared on larvae of house fly, Musca domestica L. and vinegar fly, Drosophila melanogaster Morgan, and the two soil fungi, Macrophomina phaseoli and Fusarium oxysporum. The two kinds of prey proved to be the favoured diet, accelerating development and increasing female longevity and fecundity.

Spraying of diflubenzuron at 100 g a.i./ha after spike emergence (10–15 cm from flag leaf) was more effective against early larval stages of millet spike worm, Heliocheilus (=Raghuva) albipunctella De Joannis, than spraying the crop at female flowering or at the milky grain stage.

Observations of the diurnal resting behaviour of Glossina longipalpis and Glossina fusca congolensis were carried out at Ele forest, Oke-Ako between September 1975 and May 1976 both inclusive. The two species of tsetse were observed resting most frequently on underside of stems and branches with diameter range 1–60 mm. Some G. fusca congolensis rested vertically. Whether resting vertically or obliquely, this species always rested with head pointing downwards. More than 95% of G. longipalpis and G. fusca congolensis rested between the heights of 20–240 cm. Preferred resting objects included shrubs, young saplings, climbers and, during high temperatures, bases of tree trunks.

For control purposes it is suggested from the above information that a discriminative and selective spraying of the area be planned for the late dry season and early rains when fly populations are more concentrated and individual flies tend to rest at lower heights. The spraying which should be directed to the undersurface of resting objects will help to reduce the risk of trypanosomiasis at the Oke-Ako cattle ranch.

Results of 7 years' experiments conducted in South China indicated that root-zone application of systemic insecticides effectively controlled nearly all the potential insect pests of rice—the yellow stem-borer, the striped stem-borer, the pink borer, the rice leaf folder, the rice gall midge, the brown planthopper, the greem leafhopper, the rice thrip and the rice weevil. Altogether, 16 compounds have been evaluated for the control of various species. Applications of carbofuran mixed with derivatives of nereistoxin (padan, thiocyclam or dimehypo) in the root-zone were found to be most effective against the major insect pests. The merits and demerits of root-zone applications has been discussed in this paper.

Anatomical features of cowpea (Vigna unguiculata) associated with stem and pod wall resistance to the legume pod borer, Manica testulalis, were studied. The anatomical microenvironment of the area immediately post the stem epidermis seems to impose severe limitation to larval movement and feeding within the tissue. Collenchyma cells in both 21-day old TVu 946 and IT82D-716 stems form a network of closely knit interlocking cells with a few intercellular spaces. Significant differences (P < 0.05) were observed in the distance between the epidermis and collenchyma cells of the slightly raised (convex) and concave portions of TVu 946 and IT82D-716 stems. TVu 946 had a smaller stem diameter than IT82D-716 stem. Distance between epicarp and mesocarp tissues of 7-day old TVu 946 and IT82D-716 pod wall did not show any significant difference. Similarity in cell and tissue arrangement and the absence of strengthening tissues in pod wall could be some of the most important constraints responsible for their vulnerability to larval damage.

Stem anatomy is considered to be an important factor in stem resistance to M. testulalis, but this does not appear to be the case in pod wall resistance.

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.

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.

Studies were conducted to compare adult longevity, number of host eggs parasitized and temporal pattern of oviposition of four species of Trichogramma, T. brasiliensis Ashmead, T. chilonis Ishii, T. minutum Riley and T. japonicum Ashmead. Parasitoids were reared on eggs of Corcyra cephalonica St. at 27 ± 2°C and 60 ± 5% r.h. With the exception of T. chilonis, females lived longer than males. The only thelytokous species, T. brasiliensis had the highest longevity and fecundity. However, T. chilonis was observed to lay more than 50% of its eggs on its first day of emergence. Of the four species, T. japonicum exhibited the shortest longevity and lowest fecundity.

Insects have evolved a potpourri of mechanisms for manipulating the allelochemicals that fortify their preferred host plants. A concatenation of physiological and biochemical events frequently follows the ingestion of a toxic natural product and can eventuate in a variety of fates for the compound. A particular allelochemical may be absorbed, metabolized, and sequestered, whereas the fates of concomitant natural products may be very different. Some compounds may be directly excreted in the faeces and their concentration will thus mirror that in the plant. In other cases, selective absorption and sequestration combine to biomagnify minor constituents so that the concentration of these sequestered compounds in insect tissues diners drastically from their concentrations in the host plants.

The acridid Romalea guttata is utilized in this paper as a paradigmatic insect which eclectically processes ingested allelochemicals from a wide range of host plants. This generalist herbivore is eminently suitable as a model because it feeds on plants containing a veritable pharmacopoeia of toxic compounds. The proven sequestrative potential of its defensive glands further qualifies R. guttata as an excellent candidate for determining the fates of toxic phytochemicals. An analysis of this insect's processing strategies for the compounds ingested after feeding on catnip (Nepeta cataria) reveals that for R. guttata variety is the spice of herbivorous life. The results of this investigation persuasively demonstrate that each insect species—and the phytochemical mixture that it ingests—must be regarded as a unique evolutionary case that constitutes a distinctively idiosyncratic phenomenon.

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.

The spatial distribution of the eggs and larvae of Anaphe venata Butler within canopies of its host, Triplochiton scleroxylon K. Schum situated at Araromi Village northeast of Ibadan was determined. Sampling branches of T. scleroxylon once in a spiral from base of canopy upwards was sufficient in determining the distribution of eggs and larvae of A. venata. Although the differences in the mean count of egg masses and larval groups in the lower, middle and upper canopy levels were not significant, the highest percentage of egg masses and larvae occurred on the tips of branches in the lower canopy. Sampling studies on the developmental stages of A. venata may therefore be done at the lower canopy level for best precision. Eggs and larvae are aggregated while the larval dispersion on the host suggest photo-positivity. The use of mounted, motorised elevators is proposed in order to enhance efficiency of sampling and avoid destructive sampling.

The toxicity of dursban, reldan and abate were tested against the larvae of Culex pipiens L. and Aedes aegypti (L.), in addition to evaluating effect of two bacterial toxins (Bacillus thuringiensis H-14, and B. sphaericus 1593) against C. pipiens larvae.

The synergistic effects of bacterial toxin-insecticide combinations were calculated and the new LCp-lines were determined by using a sublethal toxin dose of B. thuringiensis and B. sphaericus in combination with the three tested insecticides against Culex pipiens larvae, which was the most tolerant mosquito species.

Bacterial toxins potentiated the three used insecticides at different levels of potentiation, depending on the chemical structure of the insecticide used.

The flight phenology of the stem borer, Chilo partellus (Swinhoe) at the ICIPE's Mbita Point Field Station (MPFS) and on a nearby farmer's field was monitored using pheromone traps. The relation between pheromone trap catches of males and sorghum plant age, infestation, larval/pupal population density and sorghum cultivars used was examined. At MPFS C. partellus males were caught throughout the year in pheromone traps. Fluctuations of trap catches indicated that the pest completes two main generations on each of the long and short rain sorghum crops. On farmers' fields, males continued to be caught in large numbers after harvest, implying that the pest continues to breed on the sorghum stalks and tillers. Significantly lower observed catches of males occurred only on one (MB-3) of the eight different sorghum cultivars, during the period of 2–6 weeks after plant emergence. In general, positive correlations were observed between the number of males caught in pheromone traps and larval pupal population density, males and percentage plants infested, and males and plant age. However, the pheromone trap appeared to be less effective under high population density, particularly during the flight of the second generation moths, due to competition between pheromone trap and wild females. But the flight phenology as monitored by pheromone traps appeared to reflect major events in population development of C. partellus. Pheromone traps would be useful in detecting C. partellus and for monitoring its flight phenology.

Spatial dispersion of the nymphs of the jassid, Amrasca biguttula biguttula (Ishida), and the adults of the whitefly, Bemisia tabaci Genn. on F414, a Gossypium hirsutum variety, was systematic in Ludhiana (Punjab). Both the jassid and the whitefly displayed no definite pattern along the height of the plant, though a maximum number of whiteflies were recorded at middle canopy (21–40 cm from bottom). Sample sizes of 10–15 plants, selected in a statistically linear fashion represented populations of jassid nymphs and adult whitefly on all four varieties. Sampling jassid nymphs by visual counting and whitefly by split-cage were the most suitable sampling methods for local cotton growers among the various methods compared.