EFFECTS OF SELECTED CHEMICAL PESTICIDES ON AGAMERMIS-UNKA (NEMATODA, MERMITHIDAE), A PARASITE OF THE BROWN PLANT HOPPER, NILAPARVATA-LUGENS

Selected commercial and technical grade pesticides were tested against the egg, preparasite and adult stages of Agamermis unka, a nematode p arasite of the brown planthopper, Nilaparvata lugens. The commercial i nsecticide, diazinon (LC50=0.37 ppm), was most toxic to the preparasit es, followed by phenthoate (LC50=0.43 ppm), BPMC (LC50=0.44 ppm), IBP (LC50=0.46 ppm), cartap hydrochloride (LC50=0.82 ppm) and buprofezin isoprocarb (LC50=1.11 ppm). The least toxic commercial pesticide test ed was the fungicide, pencycuron (LC50=2.19 ppm). Out of 12 technical grade insecticides tested, phenthoate, monocrotophos, diazinon and car bofuran (LC50=0.37-0.46 ppm) were highly toxic to the preparasites, fo llowed by buprofezin, BPMC and fenitrothion (LC50=0.74-0.86 ppm). Fent hion, etofenprox, chlorpyrifos, imidacloprid and MIPC (LC50=1.11-2.19 ppm) were the technical grade insecticides least toxic to the preparas ites. Most preparasites survived for up to 24 h at the low insecticide concentrations (0.63 and 0.31 ppm). Preparasites that were exposed to BPMC for 24 ii at concentrations as high as 5.0 ppm and survived the treatments infected brown planthopper nymphs. Four selected insecticid es-chlorpyrifos, BPMC, imidacloprid and carbofuran-had significant adv erse effects on A. unka egg hatching. Eggs that were in the insecticid e solution for 168 h fared poorly with imidacloprid having the best su rvival (> 2% of the eggs hatching at 0.04 ppm). No eggs hatched front the other insecticide treatments. Three selected insecticides, BPMC, i midacloprid and chlorpyrifos, tested against adult A. unka showed that most adults survived the exposure to the insecticides between 0.31 an d 2.5 ppm. At 5.0 ppm of BPMC or chlorpyrifos none of the adults survi ved, whereas with imidacloprid 70% of the adults survived. Egg deposit ion by the surviving adults was greatly reduced in those treated with the Insecticides compared with those in the controls. Imidacloprid had some negative impact on the preparasites' ability to infect BPH nymph s, but it had the least detrimental effect of the insecticides tested on preparasite survival and on the eggs and adults of A. unka.