Impact of different insecticides on pest natural enemy and neutral complex in rice ecosystem
Loading...
Files
Date
2004
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Department of Agricultural Entomology, College of Agriculture, Vellayani
Abstract
Investigations were carried out during the second crop season of 2003-2004 at CSRC, Karamana, to assess the status of pests, natural enemies and neutrals in the rice ecosystem and to evaluate the efficacy of different insecticides on these organisms.
The results revealed that pests dominated in the rice ecosystem followed by predators, neutrals and parasitoids. The sizeable population of pests recorded were Cnaphalocrocis medinalis (Guenee), Leptocorisa acuta (Thunberg), Hydrellia philippina Ferino, Oxya chinensis (Thunberg) and Nephotettix spp. Predators were present in fairly good number. Parasitoids and neutrals were comparatively less. The neutrals observed in the study came under the family Chironomidae, Culicidae, Tanyderidae, Otitidae and Sciomyzidae. Arthropod population showed a fluctuating trend and the highest population of pests, predators, parasitoids and neutrals were at 45, 30, 60 and 15 DAT respectively.
Chlorpyrifos 50 EC + cypermethrin 5 EC was the most effective and persistent insecticide in suppressing C. medinalis. It effectively suppressed the other pests also and the persistent toxicity against them was comparatively less. It was toxic to the beneficial organisms; with shorter persistence on predators and parasitoids and the effect on neutrals was same as in carbaryl and monocrotophos.
Acephate was found to be equally effective as carbaryl against C. medinalis and H. philippina. The other pests were also suppressed with the insecticide but the persistent toxicity was less. The insecticide was observed to be toxic to predators and neutrals and safe to parasitoids.
Highest toxicity of imidacloprid was observed on Nephotettix spp., and was same as that of monocrotophos. The insecticide was found to be equally toxic to C. medinalis, H. philippina and L. acuta and the toxicity was less persistent on O. chinensis. It was toxic to all the three groups of beneficial organisms and toxicity was for a shorter period. Carbofuran granule showed immediate toxic effect only to neutrals and the delayed toxicity was exhibited on Nephotettix spp. and L. acuta. The granule was observed to be safe to predators and parasitoids.
Azadirachtin suppressed the population of pests effectively and the effect was for a shorter period. This botanical insecticide was comparatively lower in toxicity to predators, parasitoids and neutrals. Among the insecticides tested, Bacillus thuringiensis var. kurstaki showed lower percentage mortality of C. medinalis, H. philippina, O. chinensis and L. acuta and no toxic effect on Nephotettix spp. This insecticide was safe to parasitoids and less toxic to predators and neutrals.
The overall effect of these insecticides on the total population of four groups of arthropods showed that all the insecticides significantly suppressed the population of pests and predators. Acephate and Bacillus thuringiensis var. kurstaki were safe to parasitoids while azadirachtin and Bacillus thuringiensis var. kurstaki were less toxic to neutrals.
The grain and straw yield recorded and the percentage abundance of the total population of four groups of arthropods were same in all treatments including control.
The study emphasizes the need for cultivation of tolerant varieties and periodical field assessment of arthropod community. If the pest population is high and beneficial organisms are very low, pocket application of appropriate insecticides can be resorted to. The study once again asserts that insecticidal interventions are rarely needed and the four groups of arthropods regulate themselves and manage the pests and maintain the yield.
Description
Keywords
null