BIOLOGICAL CONTROL OF INSECT PESTS OF AGRICULTURAL AND FORESTRY IMPORTANCE

One of the major constraints in increasing the productivity of agricultural crops and timber yielding forest trees, is the damage caused by pests. A pest may be defined as ” any organism detrimental to man or his property in causing damage of economic importance”. It may also be defined as ” A species which because of its high numbers is able to inflict substantial harm to men, domestic animals or cultivated plants”. The pest is a broad term which includes organisms from various distinct groups like insects. Nematodes, Weeds, Rodents, birds and disease causing microbes. Out of them, insects and disease causing microbes, cause enormous damage to eco-momically important plants and plant products.

There are about one million insects, known out of which pests are about 15,000 and only 300 of them are of economic importance. These insect pests damage valuable plants of agriculture and forestry importance. Mention may be made of three insect pests one from agriculture and two from forestry.

Heliothis armigera
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Hubner syn.Helicoverpa armigera Hubner of Lepidop-tera; Noctuidae, is perceived by both farmers and researchers
I to cause serious losses to the crops. It is reported to darri’age 60 cultivated plant species and atleast 67 other species in 39 / families across Asia, Africa and Australia.lt is a polyphagous / pest and is commonly called as gram pod borer, tomato fruit I borer, cotton boll worm, American bollworm and is widely distributed. In India the ICRISAT surveys of farmers field reveal that the annual loss of major pulses like chickpea and pigeon pea exceeds $300 million per year and losses in other legumes, cotton, cereals and other crops add substantially to that total. The damage potential of H. armigera is so great that an average infestation of one larva per plant of pigeon pea can cause a yield loss of 1015 kg/ha. In Jowar, yield loss of 18-26% and in tomato 40-50% loss has been reported. Out break in the incidence of American Bollworm had reached in epidemic proportion in some districts of Andhra Pradesh and Punjab causing huge losses to cotton during 1987-88 as a result of which many farmer committed suicide. Recently, in 1993, winter proved to be worst for cotton growers of Panjab, Haryana and Rajasthan. Against expected 50 lakh bales of desi and American var. of cotton this year the yield is expected to be down by 15 lakh bales, which means a net loss of Rs.1000 crores and also loss in revenue to the state governments.

Teak (Tectona grandis), one of the most important timber yielding plant, is widely grown in the forests of Madhya pradesh, Maharashtra, Tamilnadu, etc. Its cultivation is one of the most important aspect of economy of this state of M.P. Teak suffers heavily from two lepidopteran insect pests which cause serious damage to the foliage, thus reducing the quality and yield considerably. Hyblaeapuera commonly known as teak defoliator, is a serious pest of teak whose larvae eat up whole of the leaf except midrib and thicker veins which is responsible for about 44% of loss of wood increment. Defoliation of teak foliage is followed by infestation by Eutectona machaeralis,
commonly called as teak skeletonizer, whose caterpillar eat
only the mesophyll leaving a network of veins. The growth oi
the plant is completely checked due to loss of photosynthetic
region.    \.

Conventionally, insect pests are being managed by the ( use of chemical insecticides. The indiscriminate use of insecti-  ] cides has done potential harm to the ecosystems. Dr. Ross Hall, a noted chemist and environmentalist of Canada stated   i that to-day we live in a sea of chemicals which are posing many problems.

As a result of serious problems of chemical insecticide 1 application, an awareness has developed not only among environmentalists but also among consumers, Governments and common public and now this method of pest control has not been acceptable. Sophisticated, alternative, non-chemical, pest management systems are being developed to reduce total pesticide load on the environment. One of the most significant non-chemical method of pest control is known as Biological control.

Biological control may be defined as

“The action of parasites, predators and pathogens in maintaining another organisms density at a lower average than would occur in their absence”.

Biological control is a broad term in its true sense and pathogens are a part of such control measure. Pathogens or disease causing microbes occur every where and insects too suffer from them. A number of microbes including fungi, viruses, bacteria, protozoa and nematodes are causing diseases in insects naturally, thus managing their population at a level. Sometimes the insect diseases occur in epidemic form involving a large population of insects.Such microbes can be exploited for control or management of insects pest and the system is called as microbial control. There are many advantages of using microbes for managing insects pests -
They are highly specific, thus safe to nontarget organisms.
Absence of insect resistance.
They can be easily integrated with other control measures.
They can be easily produced in large scale and their application is cheap and easy.
They have no residual activity in environment.
They occur naturally.
HPwever, there are some drawbacks also -
1 Killing time may be more as they require an incubation period.
2. Production of some microbes which are obligate in nature may be expensive as they require living host for multiplication.

It is hoped that in coming years both these limitations may be overcome with the help of biotechnology. Microbial agents may be produced in large scales, formulated and applied in a variety of ways depending upon the characteristics of entomopathogen, the pest and the crop -
(i)    Introduction: An exotic organism, is introduced in to an area where it becomes established and maintains the density of the insect population below the economic threshold.

(ii)    Augmentation: This is the strategy of increasing the density of a native entomopathogen within the insect population to maintain the pest density at an acceptable level.

(iii)    Inundation: This is an insecticidal approach. The microorganisms are propagated in the laboratory and applied in the same manner as an insecticide to pests at critical periods of the lifecycle of the pest for short term suppression of pest numbers.

(iv)    Integrated Pest Management (IPM) This strategy involves the simultaneous or sequential use of several control methods in managing insect populations. This includes use of entomopathogen,low doses of insecticides, cultural methods, other parasites, predators, etc.

Now-a-days, there has been increased emphasis on investigating the use of entomopathogens as a complete or partial alternative to chemical insecticides in the developed countries like USA, USSR and UK etc. Many commercially prodxrced microbial insecticides based on either viruses, or bacteria or fungi are available in these countries under several trade names.

A microbial preparation and formulation for use in insect control programme is called as microbial insecticides.
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