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1 July 2014 Behavioral and Electroantennogram Responses of Plum Curculio, Conotrachelus nenuphar, to Selected Noxious Plant Extracts and Insecticides
A. Gökçe, L. L. Stelinski, D. R. Nortman, W. W. Bryan, M. E. Whalon
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Abstract

Behavioral and electroantennogram responses of plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), adults were tested for several methanolic plant extracts and organically approved insecticides. Plant extracts were evaluated for their potential as antifeedants or oviposition deterrents. These extract responses were also compared to those elicited by the non-neurotoxic, organic irritant-insecticide kaolin clay. Both sexes of plum curculio exhibited antennal response as measured by electroantennogram, which ranged from 0.2 to 1.1 mV, to plant extracts and the organic irritant/insecticide, with the greatest response to the extract of rough cocklebur, Xanthium strumarium L. (1.1 mV). No choice tests were conducted to compare feeding and oviposition by plum curculio on untreated apples or on apples treated with one of the extracts or the insecticide. The insecticide pyrethrum and extracts of X. strumarium and greater burdock, Arctium lappa L., significantly reduced feeding. Also, pyrethrum, A. lappa, Humulus lupulus L. (common hop), X. strumarium, and Verbascum songaricum Schrenk extracts completely inhibited egg deposition. In no-choice assays, the effects of kaolin clay with incorporated plant extracts on plum curculio feeding and oviposition were monitored as complementary tests. A. lappa—kaolin, H. lupulus—kaolin, and X. strumarium—kaolin mixtures significantly reduced the feeding of plum curculio compared to the control or kaolin clay alone. Each of the plant extract—kaolin mixtures evaluated, with the exception of Bifora radians Bieberstein (wild bishop), completely inhibited plum curculio oviposition as compared to controls.

Introduction

Plum curculio, Conotrachelus nenuphar (Herbst) (Curculionidae: Coleoptera), is a tree fruit pest native to North America east of the Rocky Mountains. It causes economically significant damage in rosaceous tree fruit in the eastern United States, particularly in tart and sweet cherry, pome fruit, and peach (Chapman 1938). It is also known to cause damage to highbush blueberry (Polaravapu et al. 2004). Adults of both sexes feed on fruit by making a small puncture in the skin and eating the flesh underneath. Female plum curculio also make crescent-shaped oviposition scars in the developing fruit, where they lay their eggs. Both of these behaviors reduce the marketability of fruit. As a result, scar tissue and/or developing larvae feeding can cause significant yield loss in commercial orchards, and the legal prohibition or “no worm” policy in Michigan cherries (Hall 1977; USDA-AMS) effectively creates zero tolerance for plum curculio larvae in processed cherries. Today, this 1940's law has been substantially strengthened by emerging “good agricultural practices” or good agricultural practice marketing standards, along with international infestation export barriers for Upper Midwest tree fruit.

The passage of the Food Quality Protection Act (FQPA 1996) essentially has cancelled the use of key organophosphate insecticides such as azinphos-methyl (AZM) (US EPA 2008), an insecticide that sufficiently penetrates rapidly growing fruit to eliminate larvae while effectively controlling adults and leaving no or very little residue at harvest. In both international and national markets, maximum residue limit (MRL) standards with AZM use were almost never violated, while numerous “reduced-risk” (US EPA 2012) insecticides have triggered rejections in domestic and foreign markets (Whalon et al. 2011). Therefore, today's Upper Midwest growers, representing 85% of the USA's tart cherry production (NASS 2012), are seeking effective alternative means to replace AZM while achieving excellent control of internally tunneling larvae.

As AZM is being phased out (US EPA 2008), phosmet (Imidan™) as well as synthetic pyrethroids have been suggested as possible replacements in IPM programs, and its use by many growers in the Upper Midwest is increasing rapidly (Whalon et al. 2011). So far, these and other “replacement” pesticides are typically less effective for plum curculio control and require more sprays or more complicated pesticide use patterns to achieve economic control. More frequent applications result in a higher risk of resistance while negatively impacting the contribution of beneficial organisms to ecological services (Whalon et al. 2011). To date, AZM's replacement selection has not been a straightforward matter in Upper Midwest stone fruit orchards, and there is a need for additional strategies and tactics to mitigate risks of pest-inflicted damage, breach of good agricultural practice standards, and violation of maximum residue limits in foreign markets.

Conventional stone fruit producers in the Upper Midwest are not alone in the struggle to control plum curculio. Organic producers throughout eastern North America also struggle to control this key pest (Grieshop et al. 2010). The tools available generally are prohibitively expensive, very labor intensive, or impart unacceptable maximum residue limit risks in export markets. Previous work with plum curculio in Upper Midwest organic stone fruit production has introduced “attract and kill”