Integrated management of Thrips tabaci (Thysanoptera: Thripidae) on onion in north-western Italy: basic approaches for supervised control

BACKGROUND: Thrips tabaci Lindeman (Thysanoptera: Thripidae) is a major pest on onion, Allium cepa L., worldwide. In 2010, research was conducted in a commercial onion field in north-western Italy in order (i) to evaluate the efficacy of different insecticides and of the SAR activator acibenzolar-S-methyl, (ii) to correlate thrips infestation levels with bulb size and weight at harvest and (iii) to implement a reliable thrips sampling method. Efficacy of the three active ingredients spinosad, lambda-cyhalothrin and acibenzolar-S-methyl on local thrips populations were also evaluated in laboratory bioassays. RESULTS: During field surveys, the highest and the lowest thrips infestations were observed in plots treated with lambda-cyhalothrin and with spinosad and acibenzolar-S-methyl respectively. The effectiveness of spinosad was also confirmed in laboratory bioassays. At harvest, bulb size and weight did not significantly differ between treatments. A high correlation with visual inspection made plant beating a suitable sampling method for routine practice, enabling a good estimate of thrips infestation. CONCLUSION: Damage caused by thrips is often not severe enough to warrant the frequent pesticide applications the crops receive in north-western Italy. The use of spinosad and acibenzolar-S-methyl is suggested as an alternative to conventional insecticides for the preservation of natural enemies.