Helicoverpa armigera (Hübner)

Helicoverpa armigera is widely distributed in India and attacks a variety of cultivated and wild plants throughout its distribution range. On pulse crops, it is much more serious in the states of Karnataka, Maharashtra, Andhra Pradesh, Tamil Nadu, Orissa, Punjab, Gujarat and Uttar Pradesh. On grain legumes, it causes serious damage to pigeonpea, chickpea, pea, mungbean, urdbean, lentil, soybean and cowpea. Apart from pulses, it has been recorded as a serious pest of cotton, maize, sunflower, tobacco, tomato and other vegetables.

The insect prefers to lay eggs on the inflorescence of the plants. The young larva feeds on tender leaves, buds, flowers and subsequently it bores into the pods and feeds on the seeds with its head and part of the body thrust inside, the rest remaining outside. A single larva may destroy 30-40 pods before it reaches maturity.

The eggs hatch in 3-4 days. The larva completes its development in 18 to 25 days. The pupae which are formed in an earthen cell in the soil, give rise to moths in 7 to 14 days. In the laboratory, H. armigera is multiplied on chickpea-based semisynthetic diet. Pupae of H. armigera can be separated by the distance between the genital and anal pore which in females is more than double of that in the male. In addition, in the female pupae, on either side of the genital pore, a ‘V’ shaped depression or fold extending up to the tenth segment is visible. Other supplementary characters are the average length of genital and anal pores and abdominal length which can also be observed with an ordinary hand lens.

The culture of H. armigera is started by collecting the adults in light traps (inclusion of adults collected in light traps to the laboratory culture helps to increase the vigour of the culture). Helicoverpa larvae could also be collected on a large scale from its host crops in endemic areas for initiating the culture. Nucleus culture can also be obtained from the established laboratories.

The material obtained from the above methods is reared in the laboratory in aseptic conditions and the healthy progeny is selected and established.

The production plan starts with the availability of 550 pairs of adults every day which will yield 22,000 eggs daily. The adults are kept @ 100 pairs in each oviposition cage. Each cage consists of a cylindrical iron frame (50 cm h x 30 cm diameter) having two rings and with a white or black cloth enclosing the frame. A circular plastic mesh (on which cotton swabs soaked in water and honey solution are placed in small containers) rests on a support 5 cm above the base of the frame. The cloth cover is open at both ends with a 20 cm vertical slit in the centre which can be closed with a zip or cloth clips. The cloth cover enclosing the frame is tied with rubber bands at both ends and contains the moths. It is placed on an enamel or aluminum tray (40x40x5 cm) with a 3 cm thick sponge at the bottom soaked in water. Even in summer months the temperature inside the cage is maintained at 26°C and humidity at 60-90%.

The eggs are laid all over the inner surface of the cloth cover. The cloth with eggs is removed daily. The cloth containing eggs is surface sterilized in 10% formalin for 10 minutes, the eggs could also be surface sterilized by 0.2% sodium hypochloride solution for 5-7 minutes and treated with 10% sodium thiosulphate to neutralise the effect of sodium hypochlorite) rinsed in distilled water five times for about 10 minutes and eggs collected using a washing machine. The eggs are later placed on paper toweling under laminar flow hood for drying.

The dried cloth pieces containing eggs are kept in 2 litre flasks containing moist cotton. Flasks are plugged with cotton wrapped in muslin cloth and the bottom of the flask is wrapped with aluminum foil.

The larvae are reared on a semisynthetic diet. The composition and cost of diet for rearing larvae is as follows

390 ml of water is mixed with fraction 'A' of the diet in the blender which is run for two minutes. Fraction 'B' is boiled in the remaining 390 ml water. Fraction 'A' and 'B' are mixed and the blender is run again for 1 minute. Finally, fraction 'C' is added to the mixture of 'A' and 'B' in water and the blender run again for 1 minute. Formaldehyde solution is added in the end. The diet is poured as per the requirement either on the nylon mesh for rearing upto 5-7 days old larvae or in tray cells for rearing the larvae above 5-7 day old or poured into sterilized petriplates and allowed to solidify. It could be stored in the refrigerators upto 2 weeks (As over 13.3 kg diet has to be prepared daily large sized waring blenders (industrial type) have to be used; the quantity of diet ingredients has to be calculated accordingly).

The positively phototropic larvae are removed from the top of the aluminium foil wrapped flasks with a fine sterilized camel hair brush and then transferred to the diet.

220 larvae are transferred to diet impregnated on nylon mesh and placed in 25 em x 14 em x 11 em ventilated plastic containers.

100 such containers are maintained daily for 5-7 days. A total of 800 (700 + 100) containers are required.

Starting with 22,000 eggs with an estimated 5% mortality in egg stage the total larvae available is 20,900. Taking 10% mortality upto first 5-7 days the total larvae available for transfer to the trays will be 18,810 out of which 80% will be utilized for virus production i.e., 15,048 and 20% for continuation of host cultures i.e., 3762 larvae.

Diet requirements for the young larvae upto 5- 7 days at 2 gms/larva will be 4.18 kg.

Diet requirement for 15,048 5-7 day old larvae to be utilized for Ha NPV production at 4 gms / larva will be 6.02 kg.

Daily average diet required for rearing the field collected larvae for augmenting the nucleus stock will be about 1 kg.

Twenty per cent larvae which are sent to host culture unit start pupating when they are 18-19 days old and the pupae are formed within 2-3 days. The pupae are harvested from the diet and are surface sterilized by 0.2% sodium hypochlorite solution, washed and neutralized by 10% sodium thiosulphate, washed thoroughly and dried by rolling over blotting paper. The pupae are sexed and placed over moist sponge in adult emerging cages similar to oviposition cages.

The egg, larval, pupal and adult stages of H. armigera last 3-4, 18-20,7-8 and 7-9 days. The oviposition period of the females is about 5 days.

Cost of production (1993 price index) of Helicoverpa with all infrastructure available by engaging contractual workers. (This includes diet cost, electricity charges and labour charges).