This paper reviews and analyses literature on the effect of plant species diversity on crop pests. It is observed that populations of several crop insect pest species are depressed under conditions of plant species diversity. The factors responsible for this depression are: parasites, predators, masking, camouflage, repellency, less colonization, resource concentration, unfavourable microclimate, physical obstraction and trap cropping. Natural enemies account for more than half of the cases where the pest population was claimed to be regulated in the weed-diversity systems. However, under conditions of crop–crop diversity, natural enemy action accounted for less than a third of the cases reviewed. It is further observed that most of the reviewed crop–crop diversity systems were of annual crops. It is therefore concluded that under conditions of annual cropping natural enemies are probably of lesser importance than other regulating factors.

The anterior aorta is rich in axons and axonal endings originating from the nervus corporis cardiacum (NCC) and the corpus cardiacum (CC). Neurosecretory granules in the NCC axons are small compared to large granules synthesized in the CC. Vesiculation of the secretory granules into clusters of small vesicles occur both in NCC axonal endings and axon-like processes from the CC, suggesting that both types of secretions are released into the haemolymph.

Synapses occur between the NCC axons and cardiac muscle cells, as well as with cell processes from the CC, suggesting that some of the neurohormes from the NCC axons may function as neurotransmitters. The CC consists of large neuron-like cells, that synthesize an intrinsic secretion; it also contains a neuropil of NCC axons and CC cell processes. There is no evidence of a separate storage and release lobe in the CC. No synapses occur between the axons and cell processes or with the cell bodies. The CC cell processes have their endings in the aortic wall where they make synapses with NCC axonal endings and where they most likely release their material. It is suggested that in Glossina: (a) the aortic wall has taken over the neurohaemal role of the CC whose function otherwise remains that of synthesizing an intrinsic hormone; and that (b) the activity of the CC to synthesize and/or release its intrinsic secretion is most likely controlled in the aortic wall via a neurotransmitter substance.

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.

Effects of temperature on female longevity, fecundity and fertility of the sorghum shootfly, Atherigona seccata Rondani, were investigated. The longevity, preoviposition and oviposition periods, eggs per female per day, mean eggs per female and fertility (per cent eggs hatched), for the shootflies maintained at constant temperatures of 20, 25 and 30°C and alternating temperatures of 30°C (photophase) and 20°C (scotophase) referred to as 20–30°C were determined. At lower temperature (20°C), the longevity, preoviposition and oviposition periods were prolonged considerably, while daily egg production, mean fecundity and fertility were decreased. Higher temperature (30°C) had the reverse effect on preoviposition and oviposition periods as well as daily egg production. There was a significant positive correlation between the pupal weight and the number of eggs laid by the fly at 20°C. Egg mortality increased with advance in maternal age. The rate of increase in egg mortality was faster at 30°C than at lower temperatures.

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.

Phenology of Arboreum varieties: G 27, LD 133 and LD 230 differed from Hirsutum, F 414 under unsprayed conditions in Ludhiana. Protection to Arboreum varieties at seedling stage against grasshopper and to bolls formed between 1 August to 15 September against bollworm damage was found necessary. In Hirsutum variety, F 414 bolls formed between 16 August to 15 September needed maximum protection from bollworm damage.

At vegetative phase, jassid population was positively correlated with the leaf size and negatively with number of gossypol glands and leaf thickness, and that of whitefly was positively correlated with number of leaves per plant. Six plant morphological characters: number of leaves, squares, bolls, vegetative and reproductive branches and shoot pubescence-affected bollworm infestation significantly and the effect was related to and varied with the age of the plant. Anthocyanin pigment was not detected in any plant part in the four cotton varieties. At vegetative and reproductive phases, gossypol, total phenols, condensed tannins, leuco-anthocyanins and flavenols in leaf, shoot and boll per se did not influence insect pest infestations under field conditions. The parasite population was not related to pest infestations throughout the plant growth. Prédation rates, however, on pest populations seemed to be considerable. Sclereids and lignified cells affected penetration of first instar Earias vittella larvae into bolls.

Incidence of okra stemfly, Melanagromyza hibisci Spencer in India was high (40–60%) in winter months, i.e. during October, November, December and January sowings. Mean maximum and minimum temperature that prevailed 30 days after sowing had significant negative correlation with percentage main stem damage. Carbofuran, phorate, quinalphos and aldicarb, applied at 1 kg per ha reduced damage to main stem at the seedling stage but could not control subsequent damage to petioles. Eurytoma sp., a parasitoid on M. hibisci, had a high density-dependent relationship with its host, and played a significant role in keeping it under control.

A new 6a-hydroxylated pterocarpan, named hildecarpin, has been isolated from the healthy roots of Tephrosia hildebrandtii. It has been assigned the structure (−)-3, 6a-dihydroxy-2-methoxy-8, 9-methylenedioxypterocarpan on the basis of its spectroscopie data, optical rotation and chemical transformations. Hildecarpin has exhibited insect antifeedant activity against the legume pod-borer Maruca testulalis, an important pest of the cowpea (Vigna unguiculata), and antifungal activity against Cladosporium cucumerinum. This finding suggests that the pterocarpan phytoalexins formed as a result of microbial infection of the cowpea plant may constitute a basis for induced resistance in the plant against M. testulalis.

Studies on the effect of various diets on development, longevity and fecundity of Oxycarenus gossypinus were conducted in the laboratory at temperatures of 25–33°C. The mean periods of nymphal development when reared on seeds of okra, kenaf, roselle and cotton were 15.5, 15.7, 15.8 and 18.1 days, respectively.

Mated males lived longer and in decreasing order on okra (59.2 days), roselle (57.5 days) and kenaf (57.3 days) than on cotton (43.5 days). Mated females also lived longer on okra (41.4 days), kenaf (40.1 days) and roselle (39.3 days) than on cotton (32.5 days).

Mated females reared on okra seeds laid significantly the highest mean number of eggs per female per day (15.05 ± 0.87 eggs). But the mean number of eggs oviposited when fed on seeds of kenaf (12.9 ± 1.01 eggs) and roselle (10.9 ± 1.18 eggs) was not significant.

In the Chitwan valley, Nepal, Chilo partellus preferred maize and sorghum over rice, teosinte, finger millet and sugar-cane. Infestation on young maize plants produced “dead hearts” and on older plants reduced growth and sometimes prevented cob formation. The yield reduction in some maize cultivars reached 60% and stem infestation levels reached 98%. Borers produced “dead hearts” in young and “whiteheads” in older rice plants.

The egg, larval and pupal periods from April through September lasted 4–5, 16–41 and 4–8 days, respectively. A complete generation took 28–48 days under summer field conditions and 192–233 days from October to May. Of the one egg, four larval and two pupal parasitoids, all hymenopterans, which were reared from C. partellus, the two most important were Trichogramma chilonis (70% egg parasitism) and Apanteles flavipes (30% larval parasitism).

A positive mean correlation was observed between engorged larval weight and unfed nymphal weight. Similarly, positive linear correlations were observed between engorged nymphal weight and unfed adult weight, between unfed female weight and engorged female weight and between engorged female weight and egg batch weight. Positive linear correlations were also observed between scutal length and weight of unfed adult ticks and between the duration of survival and unfed weight of adult ticks at both 43 and 85% r.h. and 28°C. At 43% r.h. and 28°C, small ticks lost water faster than larger ones. At 96% r.h. and 28°C the small ticks also gained water faster than larger ones. For the sizes tested, all the male ticks were comparable in their ability to fertilize normal females, but the smallest females were incapable of reproduction.