Efficacy of ethyl formate and ethyl acetate for the control of onion thrips (Thrips tabaci).

Both adult and juvenile thrips (Thrips tabaci) reared on leeks (Allium ampeloprasum) were very susceptible to the effects of ethyl formate. Complete control was achieved at concentrations as low as 2.7 g/m³ after 2 h. Treatment of thrips-infested onions (Allium cepa) with 160 g/m³ of an aerosol containing 16.7% ethyl formate by weight in carbon dioxide killed nearly all adult thrips immediately after treatment. An assessment 9 days after treatment indicated that eggs had not been killed by the treatment. No residues of ethyl formate were detected in onions collected 1-28 days after treatment following application of two very high dose rates (236 and 756 g/m³). Ethyl formate had no effect on skin colour, onion firmness, or incidence of rots, and no visual signs of phytotoxicity were evident on onions treated with concentrations up to 324 g/m³. The highest dose of ethyl formate tested on eggs (27 g/m³ for 2 h) in small pieces of leek gave marginally lower nymph counts than the untreated control. Ethyl acetate at rates of 94 and 120 g/m³ significantly reduced the numbers of emerging nymphs compared with those emerging from an untreated control. This fumigant is a similar compound to ethyl formate but may be less phytotoxic. When ethyl formate is used for disinfestation of heavily infested onions, a second treatment is needed to control the egg stages. [ABSTRACT FROM AUTHOR]