Evaluation of alternative rice planthopper control by the combined action of oil-formulated Metarhizium anisopliae and low-rate buprofezin

BACKGROUND: High resistance of brown planthopper (BPH) Nilaparvata lugens Stal to common insecticides is a challenge for control of the pest. An alternative control strategy based on the combined application of fungal and chemical agents has been evaluated. RESULTS: Three gradient spore concentrations of oil-formulated Metarhizium anisopliae (Metschnikoff) Sorokin (Ma456) were sprayed onto third-instar nymphs in five bioassays comprising the low buprofezin rates of 0, 10, 20, 30 and 40 mu g mL(-1) respectively. Fungal LC50 after 1 week at 25 degrees C and 14 : 10 h light : dark photoperiod decreased from 386 conidia mm(-2) in the buprofezin-free bioassay to 40 at the highest chemical rate. Buprofezin (LC50: 1647, 486 and 233 mu g m(L-1) on days 2 to 4) had no significant effect on the fungal outgrowths of mycosis-killed cadavers at the low application rates. The fungal infection was found to cause 81% reduction in reproductive potential of BPH adults. In two 40 day field trials, significant planthopper (mainly BPH) control (54-60%) was achieved by biweekly sprays of two fungal candidates (Ma456 and Ma576) at 1.5 x 10(13) conidia ha(-1) and elevated to 80-83% by incorporating 30.8 g buprofezin ha(-1) into the fungal sprays. CONCLUSION: The combined application of the fungal and chemical agents is a promising alternative strategy for BPH control. (C) 2010 Society of Chemical Industry