4-Pyridyl Carbonyl and Related Compounds as Thrips Lures: Effectiveness for Onion Thrips and New Zealand Flower Thrips in Field Experiments DAVID A. J. TEULON,* ,† MELANIE M. DAVIDSON, † DUNCAN I. HEDDERLEY, § DALE E. JAMES, † CALLUM D. FLETCHER, † LESLEY LARSEN, # VANESSA C. GREEN, # AND NIGEL B. PERRY # New Zealand Institute for Crop and Food Research Limited, New Zealand On the basis of structural and/or aroma analogies to known thrips (Thysanoptera: Thripidae) lures, 35 compounds (18 pyridine derivatives, 13 benzene derivatives, and 4 other compounds), consisting of both synthetic and naturally occurring compounds, were screened for their ability to bring about increased thrips capture in field experiments using water traps in Canterbury, New Zealand. Most of the thrips caught were New Zealand flower thrips (NZFT) (Thrips obscuratus) or onion thrips (OT) (Thrips tabaci). The greatest increase in capture for NZFT (158 times for ? cf. to water control) was for the known lure ethyl nicotinate, a 3-pyridyl ester. Ethyl isonicotinate, the 4-pyridyl regioisomer of ethyl nicotinate, not previously reported as a thrips lure, provided the greatest increases in capture for OT (31 times) of any of the compounds tested, significantly more than ethyl nicotinate. Other 4-pyridyl carbonyl compounds, including ethyl 4-pyridyl ketone, also increased OT capture significantly. The natural floral compound cis-jasmone, which increased trap capture of NZFT (? 42 times, / 25 times) but not OT, is reported as a thrips lure for the first time. KEYWORDS: Thrips obscuratus; Thrips tabaci; lure; attractant; pyridine carbonyl; benzene carbonyl; flower aroma compounds; semiochemical INTRODUCTION Thrips (Thysanoptera), especially flower-inhabiting species, are important pests of a number of agricultural and horticultural crops (1, 2). Some thrips species are very difficult to control because of various biological attributes (e.g., polyphagy, vagility, rapid reproduction, cryptic behavior) and because they have become resistant to a range of insecticides (3, 4). Consequently, there is a strong interest in developing alternative methods to insecticides for thrips pest management including the use of semiochemicals (chemicals involved in communication between organisms) (5, 6) such as plant-derived allelochemicals (7-14) and alarm and sex pheromones (15-19) or their synthetic mimics. Such chemical lures could be used in a number of applications for thrips pest management including improved monitoring, mass trapping, push-pull, lure and kill, and lure and infect strategies (16, 19, 20). Nevertheless, the behavioral responses of thrips to these behavior-modifying chemicals are not well understood: thrips walk upwind in Y-tube olfactometers (attraction), but their flight is inhibited in wind tunnels (chemokinesis) (12, 20-22) by certain chemicals. In this paper, we use the term “attractant” to refer to those compounds that bring about increased trap catch in comparison with control traps, even though the actual mechanism that brought about that increase may be different (e.g., an arrestant). Various non-pheromone chemical attractants have been identified for several thrips species through the screening of odor chemicals derived from plants (especially flowers) and compounds reported to elicit responses in other insects (10, 12, 13, 23-27). Additionally, Imai et al. (14) examined the response of thrips to compounds related to already known thrips attractants. Two compounds have given increases in thrips capture of >100 times in field experiments [methyl anthranilate for Thrips hawaiiensis (14) and ethyl nicotinate for T. obscuratus (28)], but the responses were generally much lower for other thrips species to these and a range of other compounds. In our search for new and potent thrips attractants for key thrips pests, we selected compounds related to known attractants by their chemical structures and/or by their aromas (as perceived by humans). Most of the known non-pheromone thrips attractants contain a benzene ring conjugated to a carbonyl group (e.g., benzalde- hyde, p-anisaldehyde, salicylaldehyde, Figure 1)(29, 30). More recently further benzene carbonyl compounds have been re- ported as thrips attractants [e.g., 2-aminoacetophenone, methyl salicylate, and methyl anthranilate (13, 14, 27), Figure 1]. One * Author to whom correspondence should be addressed (fax +64 3 325 2074; e-mail teulond@crop.cri.nz). † Private Bag 4704, Christchurch, New Zealand. § Private Bag 11 600, Palmerston North, New Zealand. # Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand. 6198 J. Agric. Food Chem. 2007, 55, 6198-6205 10.1021/jf070389a CCC: $37.00 © 2007 American Chemical Society Published on Web 06/29/2007