Insecticidal δ-endotoxins of Bacillus thuringiensis, Cry IA (a, b and c) were prepared from over-expressing cells of Escherichia coli and bioassayed against the third instars (6-day-old) of the spotted bollworm, Earias vittella Fabricius (Lepidoptera: Noctuidae), using artificial diet. The median lethal concentration (LC50) values were calculated for 6 days of exposure to δ-endotoxins. Cry IA(a) was found to be the most toxic (LC50 141.2 ng/cm2) followed by Cry IA(a) and Cry IA(b) with LC50 values of 224.5 and 300.5 ng/cm2 respectively. A highly significant reduction in larval weight took place in the surviving larvae treated with sub-lethal doses of the insecticidal crystal proteins.

The influence of host presence, age and mating on calling behaviour of the female spotted bollworm, Earias vittella, was studied under a 14L:10D photoperiod. Onset of calling was earlier in the presence of a host and 93% of the females initiated calling in its presence on day one after emergence, compared to 67% in its absence. A majority of the females initiated calling during the 10th hour of the first scotophase and thereafter the initiation shifted to earlier hours as age advanced. Females generally called longer in the presence of a host. The mean time spent in calling, from the 1st to the 10th day increased from 56 to 152 min in the absence of a host, and from 77 to 234 min in its presence. Most of the females resumed calling after mating, but the mated females exhibited a significant reduction in calling performance when compared with the virgin 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.

Earias vittella (Fabricius) feeds on some malvaceous plant species, but has never been reported to attack Thespesia populnea Cav., even though this plant belongs to the same family. The factors responsible for the failure of E. vittella to establish on T. populnea were, therefore, studied. When whole fruits or fruit pericarps of this plant were provided as larval food, larvae failed to develop and none of them pupated. However, on developing seeds of these fruits, larval growth and development were normal and comparable to those of larvae reared on developing seeds of the most favoured host plant, Abelmoschus esculentus Moench. Ether extracts from fruit pericarps exhibited antifeedant and antibiosis activity against this insect. Ether as well as ethanol extracts affected oviposition to some extent. In a choice situation, significantly less eggs were laid on treated than on untreated okra fruits. However, in a no-choice situation most of the eggs were laid on treated okra fruits.

Artificial diets were formulated and evaluated for their suitability to rear the spotted bollworm, Earias vittella, a major pest of cotton and okra. The most satisfactory diet consisted of maize semolina 11%, wheat bran 4.6%, soybean powder 2.4%, yeast 1.4%, salt mixture 0.9%, ascorbic acid 0.3 %, cellulose 0.9 %, agar 1.8%, water 76.7% and preservatives. The insect was reared on this diet for 10 generations without any adverse effect on its development and reproductive potential.

The susceptibility of 23 cotton genotypes to spotted bollworm, Earias vittella, was studied under natural infestation during 1977 and 1978 rainy season at Delhi, India. There were substantial differences in bollworm damage and larval population in different genotypes. Damage in shed squares and bolls was higher than in green bolls picked up from the plant. The damage/larval population in the less susceptible cultivars (Hindiweed, XG-15, HR-26 # 8XH · HG-6-IN and Sanguineum) was lower than in the susceptible check (BJR) and the trial mean. The differences in susceptibility were more pronounced at the moderate damage levels and that the damage in less susceptible cultivars increased or decreased according to the insect pressure.

There were significant differences in the gossypol, tannins, moisture, phenols and sugar content among the genotypes tested. Gossypol, tannins and moisture content of bolls and squares were negatively correlated with bollworm damage and larval population. Free phenols showed negative, but lower correlation coefficients with bollworm damage. Sugars contributed towards susceptibility while nitrogen content of bolls did not show any effect on bollworm damage. The less susceptible cultivars had higher amounts of gossypol and tannins. Some genotypes showed ovipositional non-preference because of smooth leaves.

Many factors appeared to influence the genotypie susceptibility to spotted bollworm, of which gossypol, tannins and ovipositional non-preference (due to smooth leaves) were the major factors. Gossypol and smoothness are genetically inherited and can be manipulated through crop improvement. The rating of the number and size of pigment glands on the calyx tubes and hairiness on the under surface of leaves can be used as important marker characters in breeding for spotted bollworm resistance.

The oviposition behaviour of spotted bollworm, Earias vittella Fab. was studied on 23 cotton genotypes under field and laboratory conditions. There were substantial differences in the number of eggs laid on different genotypes. More eggs were deposited on the bolls compared to leaves and squares. The relative oviposition preference differed under the field and laboratory conditions in the case of some genotypes. Leaf hairiness was significantly and positively correlated with number of eggs laid both under field and laboratory conditions. The effect of oviposition on varietal susceptibility appeared to be modified through other factors, such as gossypol and tannins. However, oviposition non-preference was one of the important resistance mechanisms in some cotton genotypes.