Tomato bollworm, the major insect in tomato farming of Nepal

                                                                       Sushil Nyaupane,MS Entomology,AFU,Nepal
Introduction
I have seen tomato bollworm as the major threat for tomato growers in Nepal. In Bajhang district, far-western region, the tomato bollworm is seen as the major insect pest in tomato which is significantly reducing the production of tomato and its quality. Farmers of tomato are not very aware about this problem in most of the areas of Nepal. So, effective information about tomato bollworm and its management methodology should be provided to the farmers.
Tomato bollworm is the highly polyphagous pest species because it feeds on many species of plants like chick pea, pigeon pea, cotton, tomato, maize, tobacco,okra,sunflower and some wild species of fruits.This insect is becoming widespread and generally this is found up to sub-tropical region of Nepal.

Fig. Helicoverpa armigera(tomato bollworm) in fruit of tomato

Life cycle
The egges are deposited generally on the upper side of leaves, flowers, bracts, buds and other reproductive parts also. The eggs are 0.5 mm in diameter and generally takes 2 to 5 days to hatch. The color of egg is white to brown.Larval period is 13-22 days and there are 6 stages of larval development. The color of larvae is green and sometimes yellow to red brown.The pupae takes 10-15 days to develop in the soil and in some species like cotton, larval stage is inside the boll also.Their color also ranges from dark brown to red brown.The adult also varies in color i.e. from reddish brown to whitish green-brown. Adult female bollworms are able to lay fertile eggs profoundly in suitable environment.
Nature of damage
They are voracious feeders so their nature of damage is substantial in production of tomato.The caterpillars bore into the fruits and feed on inner content and makes hole on the fruit so that its quality also deteriorates substantially. The nature of damage also depends upon the season and parameters of environment.
Natural enemies
Spiders,ants, lacewings and some bugs feed on bollworm eggs and larvae.There are more common parasitoids like trichogramma, telenomus etc. which are egg parasitiod. Larval parasitoid feed on larvae suchas microplitis, netelia, heteropelma etc.The nucleopolyhedrosis virus HaNPV and the fungus disease caused by Beauveria bassiana is also important enemy of tomato bollworm.
Management
1. Good cultural practices helps to reduce pest population like deep ploughing,crop rotation and avoidance of ratooning.Tolerant varities can be grown and maize and cowpea can be grown in borderstrips.Weeding is also necessar to check the growth of larvae of bolloworm and disposition of soil by wintertillage is regarded as good practice to kill larvae.
2.Pheromone traps are effective for management of bollworm and for its monitoring also.
3.Biological control :
The tomato bollworm can be checked by releasing egg parasitoids like Trichogramma chilonis@150,000/ha from 45 th day onwards at 10-15 days interval.
Releasing of predators like Chrysoperla can suppress the insect population.
Use of Nuclear polyhedrosis virus@ 250 larval equivalent/ha from 35-60 day of crop stage.
Application of Bacillus thuringiensis var. kurstaki@1kg/ha. when larvae are young.
Application of fungal pathogens like Beauveria bassiana, Metarhizium anisopliae has good result under humid condition.
Neem based bio-pesticides like nemarin, need seed kernel extract are very effective.
4. Chemical control
To control this insect various insecticide like cypermethrin, deltamethrin chloropyriphis etc. are recommended.
References:
G.C., Y.D.&K. Siegfried.2013.Crop pests of Nepal and their management.Nepal
http://www.atlasagro.com/documents/Technical brochure_BP1.pdf

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