Biological control of insect pests in NE India

KI Singh / SM Haldhar *

The economy of the North Eastern States is mainly rural and agrarian. The region offers scope for cultivation of a wide variety of agricultural crops because of its diversities in topography, altitude and climatic conditions. The major crops grown are rice, sugarcane, potato, wheat, maize, ginger, cardamom, pulses, oilseeds, tea, flowers, fruits and vegetables. There are severe pest problems on several crops grown in this region.

The North Eastern region represents an important biodiversity hotspot, one of the 25 global biodiversity hotspots currently recognized. It is important to preserve this region and help conserve the biodiversity of the region.

Pesticide consumption pattern in the region indicates that Assam consumes 0.4 to 0.6 kg ha-1 and Meghalaya 0.3 to 0.4 kg ha-1. Data on the pesticide load in the environment indicate that substantial areas in Assam carry a pesticide loan of 7-10 kg sq. km-1 while in Meghalaya, Nagaland and Manipur it is 1.3 kg sq. km-1.

However, it is encouraging to observe that there has been a reduction in pesticide consumption in the last decade in most of the States. The need of the hour is to search for potential natural enemies of the major pests of the region and we can be sure the search would yield promising results.

It would be a folly and also counterproductive to resort to the use of chemical pesticides to check insect pests and diseases in the crops grown in this region, as they would indiscriminately kill the natural enemies along with the pests themselves. Indigenous natural enemies could effectively reduce pest numbers and conservation biological control could form the backbone of IPM for various pests.

There is a need to set up mass production units for the production of some biocontrol agents and the opportunity is there for rural youth and women to come forward and set up such units to help the farmers of the region.

Biological control in rice is an important crop occupying about 40 lakh hectares in the North Eastern States. Pesticide usage is minimal in the region on rice. Thus the natural enemy complex in the agro-ecosystems of all these States has not been adversely impacted. Conservation biological control, which is the recommended practice in rice, can easily be adopted in these States.

In the case of some pests like the rice yellow stem borer and leaf folder inundation biological control may also have to be adopted. Rice insect pests have had long, close associations with their natural enemies allowing stable relationships to develop.

Predator and parasitoid guilds recorded in rice ecosystems belong to ten orders and 57 families of predators and three orders comprising 40 families of parasitoids, indicating the great diversity and richness of the natural enemy community in rice. The interactions of such predators, parasitoids and insect pathogens are the cornerstone of modern integrated pest management programs in rice.

The collective importance of natural enemies to pest population regulation is clearly demonstrated by observing outbreaks of insect pests after the removal of natural enemy communities by a broad-spectrum insecticide. The rice plant can withstand and compensate for over forty percent tiller loss during the early vegetative stage without significant reduction in yield. This gives natural enemies the requisite time to colonize and build up their populations so that they are there in numbers large enough to suppress the pests when they appear.

Conservation biological control in rice is the modification of the environment or habitat in combination with judicious use of pesticides in order to conserve natural enemies and enhance biological control.

Environment management to enhance biological control has proven valuable in many settings and appears to be very important for rice insect pest management. Conservation biological control contains two elements: judicious use of insecticides and modification of the environment. Insecticides are more harmful to natural enemies than to pests.

There is extensive evidence that the destruction of natural enemies by broad-spectrum insecticides leads to reduced biological control and the subsequent resurgence of some pests. Insecticide overuse is most damaging early in the season. Such circumstances create outbreaks of secondary pest such as brown plant hopper and impair biological control of some key primary pests such as stem borers. Insecticides are generally being misused in rice. Preventive use of insecticides in rice is common and widespread.

Preventive use of insecticides is detrimental to biological control, pest management as a whole, the environment and human health. Judicious use of insecticides is essential of for natural enemy conservation and for the enhancement of natural biological control.

In order to conserve indigenous natural enemies and enhance natural biological control, the following strategies for insecticide use are recommended:
1. Preventive or calendar-based use of insecticides should be stopped.
2. Early season spraying during the first 40 days after transplanting should be avoided.
3. Selective insecticides should be used only when pest population density reaches a damaging level.
4. When using insecticides, use appropriate formulations in the right dose. Apply at the optimum time of intervention following proper application methods. Broad-spectrum hazardous insecticides should be avoided. If available, use rice varieties that possess host plant resistance to major insect pest.
5. Modification of environment: The immediate crop environment cab be internationally modified tofavor natural enemies.

Habitat management should be aimed at providing environmental requisites to natural enemiessuch as: alternative hosts or prey; complementary foods – honeydew, pollen, nectar; over-wintering or off-season shelter; modified climate – windbreak. Some habitat management activities that have a positive influence on the abundance of the natural enemies of rice insect pests.

Vegetated rice bunds support many herbivore species (including a few pests) and many species of natural enemies. They can be a very important source of natural enemy colonization in rice fields just after planting. Rice bunds are important sources of biological control agents of arthropods. Bund vegetation provides alternative and supplementary food for predators and parasitoids.

The importance of bund fauna on the early arrival of spiders for biological control of BPH has been demonstrated experimentally. Bunds also provide shelter for natural enemies at critical times during harvesting, land preparation and between seasons. Puddling (tillage in presence of water) can have drastic effects on natural enemy populations.

Many natural enemies take shelter on the rice bunds at puddling and the presence of vegetation on the bunds greatly increases their survival. Generally, grasses and other vegetation in habitats adjacent to rice fields serve as habitats of natural enemies and also provide supplementary and complimentary food, over- wintering, or off-season habitats. Some cultural practices seriously affect natural enemies.

These include: burning of rice stubble and/ or straw; trimming of non-rice vegetation from rice bunds prior to tillage (puddling); destruction of vegetation on the field during fallow periods; strictly synchronous rice planting over a large area. From plant nutrient and natural enemy conservation points of view, it is better to incorporate crop residues into the soil rather than burn them.

If burning is essential then it should be done in heaps rather than burning residue spread all over the fields. In many countries insect predatory birds, toads and frogs are caught in rice fields for consumption. Conservation of insect predatory birds frogs and by preventing capture from the rice environment canalso enhance biological control of rice insect pests.

For effective biological control method used against rice stem borers (Scirpopha-gaincertulas and S. innotata) is the use of parasitoid. The majority of parasitoids belong to the orders hymenoptera and Diptera. Trichogramma, the egg parasitoid under order hymenoptera parasitizes on eggs of more than 200 insect pests of rice, sugarcane and cotton. T.chilonis and T.japonicum are the two predominantly used species in India.

The present work was conducted in the farmer’s field with an aim to evaluate the performance of T.japonicum, in comparison to chloropyriphos and Azadirachtin against rice stem borer (S.incertulas and S.innotata). Trichocards containing sterilized eggs of T.japonicum were taken from the State Bio Control Laboratory, Guwahati, Assam for this trial. The cards were used in the paddy field before emergence of the adult parasite.

T.japonicum @50000 ha-1 were released eight times at weekly interval starting from 30 days after transplanting of paddy. The release of Trichogramma was coincided with the egg laying period of rice stem borers. Each Trichocard were cut into 6 pieces and evenly kept over the entire field by fixing them to the inner side of the leaf of the plants by using stapler. Trichocard were stapled in the morning hours and just before emergence to avoid predation.

Paddy ecosystems are richly endowed with natural regulatory mechanisms to take care of the insect pests and entomopathogens are one of the major groups among the natural enemies. Of the eleven insect pathogens reported to attack stem borer, Bacillus thuringiensis is the major one. Against leaf folder, eighteen fungal, two bacterial, two viral pathogens and two entomo-pathogenic nematodes have been reported.

Among the entomopathogens reported on plant and leafhoppers, the fungi, Pandora delphacis, Metarr-hizium-flavoviridae, Beauveria bassiana, Erynia radicans, Entomophthora, Entomo-phagaaulicae and Fusarium sp. have shown promise. Though the natural action of entomopathogens against the pests has been well documented and reported their inherent ability to naturally regulate the pest populations below the economically damaging levels, has not been evident.

Biopesticides were also developed as key components of integrated pest management (IPM) programs, mainly as a means to reduce the load of synthetic chemical products that are being used for control of pests. The biopesticides used so far fall into two major categories viz., microbial pesticides and botanical pesticides (Ranga Rao et al., 2007).

Microbial pesticides contain a microorganism (bacterium, fungus, virus, protozoan or alga) as the active ingredient which is relatively specific for its target pest(s). The most widely known microbial pesticides are derivatives of the bacterium Bacillus thuringiensis (Bt) which produces a toxin protein that is harmful mainly to lepidopterans. Rath (1999) found that BTK II and Dipel 3.5% were more effective than Delfin 85% and Biolep.

It is also observed that Bioasp, Biolep, Biotox, dipel and Delfin @ 2000 g a.i. ha-1 were as effective as standard chlorpyriphos @ 250 g a.i. ha-1 against leaf folder.

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