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

Abstract

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 northwestern 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 lambdacyhalothrin 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.

Impact of control strategies on Thrips tabaci and its predator Aeolothrips intermedius on onion crops

“…No differences between mortality of 281 predatory and onion thrips were recorded with spinosad (where no thrips survived in any of the 282 cases) or acibenzolar-S-methyl (ANOVA: df = 1, 20; F = 0.028; 1.074; P = 0.868; 0.312; n = 15, 7). During the field experiments in this study, the untreated plots did not exhibit the highest 316 onion thrips levels, as had been observed previously (Mautino et al 2012). In this instance of low 317 thrips infestation, the untreated plots presented the best solution; this strongly supports the 318 importance of a supervised control based on pest monitoring before spray applications.…”

“…Adult survival in vials treated with this active ingredient was not 380 significantly different from that observed in the untreated control. Therefore, in the absence of the 381 plant, there is no side effect of acibenzolar-S-methyl on thrips, as previously observed in the vial 382 bioassay under the same experimental conditions (Mautino et al 2012). 383…”

“…Moreover, a substantial co-regulation or 367 cross-talk among the salicylate and jasmonate plant defense pathways has been demonstrated 368 (Schenk et al 2000); however, it is not fully understood how this signal interaction affects plant 369 response to thrips damage (Abe et al 2012;Thaler et al 2002). In the field experiments, 370 acibenzolar-S-methyl ensured low infestation levels of thrips on June 23 and July 4, as already 371 observed with high infestation levels (Mautino et al 2012); nonetheless, acibenzolar-S-methyl was 372 unable adequately to control the T. tabaci population at the following sampling dates when plants 373 started to wither. Therefore, its effects on herbivores could be mediated by plant phenology.…”

“…Thrips tabaci, thrips predators including anthocorid, mirid 113 bugs (Hemiptera: Anthocoridae, Miridae), and predatory thrips (Thysanoptera: Aeolothripidae) 114 were detected during field surveys. Plant beating was chosen as the sampling method for its high 115 feasibility, and because a strong relationship between this method and visual inspection has 116 previously been observed, and also for the larval population, generally underestimated with the 117 beating sampling method (Mautino et al 2012). Five plants were randomly selected at three points 118 in each plot (15 plants per plot), and these were beaten over a plastic tray (350  250 mm).…”

“…The toxicity of tested products was evaluated on T. tabaci and predatory thrips using the vial 142 bioassay method described by Mautino et al (2012), which is an adaptation of the thrips 143 insecticides bioassay system (TIBS) described by Rueda & Shelton (2003). Thrips were collected 144 from rearing jars and placed into a plastic microcentrifuge tube previously treated with the product 145 being tested; the tube cap contained a small well with 10% sugar-water solution.…”