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Practices to increase activities of natural enemies

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1. Certain weeds in rice environment are infested with insects that alternatively support rice pest parasitoids in off-season. Nanophyes sp. on Ammania baccifera L. a weed in rice fields have been identified as a reservoir host supporting parasitoids like Neanastatus cinctiventris Girault on gall midge, Trichomalopsis sp. on Pelopidas mathias (Fabr.).

2. Besides, predating directly on rice pests, spiders support certain parasitoids that also attack rice pests.
Paraphylax sp. and Trichomalopsis sp. parasitizing eggs of spiders have also been recorded as egg parasitoids of Oxya sp., a grasshopper on rice.

3. Trichomalopsis sp. and Elasmus sp have been recorded on the chysomelid beetle Lema. sp. a leaf feeder on Commelina sp. a common weed in the irrigation channels and rice fields. Midges on the grass host Paspalum sp., Cynodon sp. and Mnesihia sp. have been identified as reservoir hosts of gall midge parasitoids.

4. Presrvation of such reservoir hosts may be encouraged to conserve the parasitoids.
Intercropping of crop plants like mustard and alsi etc. provide nectar to the parasitoids and support their population.

5. Flowers of certain ornamental plant, Lantana sp. are also visited by scelionids and trichogrammatids for nectar. Some times certain varieties support more natural enemies than other varieties.

6. On several occasions parasitoid population reaches its peak only after the pest population has reached its peak indicating delayed density dependence.

7. Early inundative release of the specific parasitoid under such situation proves beneficial. Some of the factors that adversely affect the activities of natural enemies are indiscriminate or prophylactic use of insecticides, cannibalism, hyper parasitism and the fragile rice ecosystem.

8. Insecticides, therefore, should only be used as a last resort. Between spray and granular formulations the latter is found to less toxic to parasitoids.

9. Practice of seedling root dip @ 0.02% chlorpyrifos for 12 hours before transplanting prevents early stage pest infestation and does not disrupt the activity of natural enemies. Alternatively use of botanical products and biopesticides does not reduce parasitoid population. Organic farming may be encouraged for a eco-friendly exploitation of bio-components operating in the rice field.

9. Conservation of existing natural enemies and maximizing their impact seems more important than introduction of new ones.

10. Using more selective insecticides, applied at the best time and only when needed, alternatively application of botanical insecticides more safe to natural enemies, provision of hibernacula, shelter, pollen and nectar producing plants, reservoir hosts or weed hosts in the rice environment are some of the methods available.

11. Efforts to educate farmers in recognizing natural enemies and the beneficial role played by them are important as the role played by the parasitoids remain unnoticed. Utilization conservation of natural enemies in situ in the rice ecology is the most practical option available for promotion of natural biocontrol.

12. One of the important approaches for this is to stop unnecessary use of insecticides as a prophylactic measure or even when the pest population is below economic injury level in particular, against foliage feeders like leaffolders and internal feeders like YSB at vegetative stage of the crop.

File Courtesy: 
CRRI
Photo Courtesy: 
CRRI
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