4-pyridyl carbonyl compounds as thrips lures: Effectiveness for western flower thrips in Y-tube bioassays

In a search for chemical lures to manage the cosmopolitan crop pest western flower thrips (WFT), Frankliniella occidentalis, a Y-tube olfactometer was used to screen 20 compounds, including 18 4-pyridyl compounds. Comparison of Y-tube results for New Zealand flower thrips (NZFT), Thrips obscuratus, with field trapping data for ethyl nicotinate and ethyl isonicotinate, suggested that the minimum attractive dose (MAD) of an odor compound, where significantly (p < 0.05) more than 50% of thrips walked up the odor-laden arm, provided a measure for selecting compounds to evaluate for potential lure efficacy in the field. Eighteen synthetic 4-pyridyl compounds were tested on female WFT in a Y-tube olfactometer and four 4-pyridyl carbonyl compounds had MADs lower than the known WFT attractants p-anisaidehyde (MAD 10(-3) mu L) and ethyl nicotinate (10(-2) mu L): methyl isonicotinate (10(-6) mu L), ethyl-2-chloropyridine-4-carboxylate (10(-6) mu L), ethyl isonicotinate (10(-4) mu L) and methyl 4-pyridyl ketone (10(-5) mu L). The suitability of MAD for selecting compounds for further evaluation of practical lure efficacy is discussed. Comparisons of activities within homologous series of esters and ketones showed that attractant activity decreased with chain length. 4-Formyl pyridine was an attractant at a dose of 10(-5) pL, but was repellent at higher doses (10-2-10 degrees mu L).