Development of a Synthetic Plant Volatile-Based Attracticide for Female Noctuid Moths

Australian Journal of Entomology (2010) 49, 10–20 Development of a synthetic plant volatile-based attracticide for female noctuid moths. I. Potential sources of volatiles attractive to Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)aen_733 10..20 Alice P Del Socorro,1,2* Peter C Gregg,1,2 Daniel Alter2 and Chris J Moore3 1Cotton Catchment Communities Cooperative Research Centre, Narrabri, NSW 2390, Australia. 2School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia. 3Animal Research Institute, Queensland Department of Primary Industries and Fisheries, Yeerongpilly, Qld 4105, Australia. Abstract This paper is the first of a series which will describe the development of a synthetic plant volatile-based attracticide for noctuid moths. It discusses potential sources of volatiles attractive to the cotton bollworm, Helicoverpa armigera (Hübner), and an approach to the combination of these volatiles in synthetic blends. We screened a number of known host and non-host (for larval development) plants for attractiveness to unmated male and female moths of this species, using a two-choice olfactometer system. Out of 38 plants tested, 33 were significantly attractive to both sexes. There was a strong correlation between attractiveness of plants to males and females. The Australian natives, Angophora floribunda and several Eucalyptus species were the most attractive plants. These plants have not been recorded either as larval or oviposition hosts of Helicoverpa spp., suggesting that attraction in the olfactometer might have been as nectar foraging rather than as oviposition sources. To identify potential compounds that might be useful in developing moth attractants, especially for females, collections of volatiles were made from plants that were attractive to moths in the olfactometer. Green leaf volatiles, floral volatiles, aromatic compounds, monoterpenes and sesquiterpenes were found. We propose an approach to developing synthetic attractants, here termed ‘super-blending’, in which compounds from all these classes, which are in common between attractive plants, might be combined in blends which do not mimic any particular attractive plant. Key words kairomone, moth attractant, olfactometer, plant volatile. INTRODUCTION 2002; Meagher 2002; Meagher & Landolt 2008). In this series of papers, we discuss the theoretical underpinning of this Plants emit volatile compounds that mediate insect–plant development as well as the demonstrations of field efficacy, interactions. These compounds can have either attractant or non-target impacts and other data required for registration of repellent effects which can potentially be exploited to aid pest products such as Magnet®. This paper describes the identifi- management. We have recently registered an attract-and-kill cation of potential sources of attractive volatiles, and a novel product (Magnet®) for use in integrated pest management approach to their combination in attractive blends. of the important noctuid pest species Helicoverpa armigera The cotton bollworm, H. armigera, is an important eco- (Hübner) and H. punctigera (Wallengren) in Australian cotton nomic pest of cotton and many other summer crops in Austra- and other crops (Australian Pesticides & Veterinary Medicines lia. The larvae are highly polyphagous, usually feeding on Authority 2009). To our knowledge, this is the first synthetic the fruiting bodies, and the moths are attracted to many plants plant volatile-based attracticide which has been commercial- either as food sources or oviposition sites (Zalucki et al. 1986; ised for noctuid pests of agriculture, despite the identification Firempong & Zalucki 1990). In non-transgenic cotton, control in the laboratory of several attractive volatile compounds in of this pest has usually been through insecticides targeted at various host plants (Landolt 1989; Haynes et al. 1991; Heath the larvae, which has led to H. armigera developing resistance et al. 1992; Hartlieb & Rembold 1996; Bruce & Cork 2001; to a number of insecticides (Forrester et al. 1993). To help curb Rajapakse et al. 2006), and experimental demonstrations of resistance as well as to reduce environmental problems with the attractiveness of both crude plant extracts and synthetic insecticides, the cotton industry has adopted an integrated mixtures in the field (Zhu et al. 1993; Shaver et al. 1998; pest management approach including a resistance manage- Landolt & Alfaro 2001; Landolt et al. 2001; Landolt & Higbee ment scheme for H. armigera (Farrell 2008). More recently, the extensive use of transgenic cotton expressing Bt toxins in Australia (Fitt & Cotter 2005) has required the widespread *[email protected] adoption of resistance management plans (Andow et al. 2008). © 2010 The Authors Journal compilation © 2010 Australian Entomological Society doi:10.1111/j.1440-6055.2009.00733.x Plant volatiles as moth attractants 11 A range of approaches, including chemical, cultural and feeding on nectar from these plants. For the purpose of devel- behavioural manipulation, is incorporated in these plans. oping attract-and-kill formulations, the ecological basis of the However, there remains a need for new tools, including attrac- attraction is of less consequence than the level of attraction, ticides targeted at female moths (Gregg et al. 1998). In non- and whether it varies according to the sex or mated status transgenic cotton, removing female moths from the population of the moths. could reduce oviposition, thus reducing the need for insec- In this paper, we report the attractiveness of various host ticides and allowing other components of integrated pest and non-host plants to unmated H. armigera moths in the management to work more efficiently. For transgenic cotton, laboratory using an olfactometer. We document the volatile selective removal of potentially resistant moths using attracti- compounds emitted by these plants which might be used in cides could reduce the frequency of resistance alleles. Alter- attract-and-kill formulations, and describe an approach to natively attraction of female moths to refuge crops where they developing these formulations which does not involve mim- might subsequently oviposit could enhance the production of icking the volatile emissions of particular attractive plants. moths which have not been exposed to Bt toxin, an important objective of the resistance management strategy (Farrell 2008). MATERIALS AND METHODS The attractiveness of plants and plant odours to Helicoverpa spp. and other noctuid moths is well documented. Extracts Experimental insects from pigeon pea, Cajanus cajan, were shown to be attractive Laboratory-reared H. armigera moths from an insect culture to H. armigera moths (Rembold & Tober 1987; Hartlieb & maintained in an insectary were used in the bioassays. The Rembold 1996). Rembold et al. (1991) demonstrated the culture originated from larvae collected from chickpeas in the attractiveness of a synthetic chickpea (Cicer arietinum) Darling Downs region of southern Queensland, and had been kairomone to H. armigera moths in laboratory and field maintained in the laboratory for at least 10 generations. Larvae experiments. Floral compounds identified in the African mari- were reared individually in 35 mL plastic containers and gold, Tagetes erecta, and their synthetic equivalents were provided with a small block of soybean-based artificial diet found to be attractive to H. armigera females (Bruce & Cork (Teakle 1991). Rearing conditions were 25–26°C, approxi- 2001). In the USA, volatiles emitted by the night-blooming mately 50% humidity and 16L : 8D photoperiod, with the dark Gaura spp. have been shown to be highly attractive to Heli- period between 09:30 and 17:30 h Australian Eastern Standard coverpa zea (Boddie) and other noctuid moths (Beerwinkle Time (AEST). Day lighting was provided by six 40 W white et al. 1996; Shaver et al. 1998). The attraction of the cabbage fluorescent tubes, and four 150 W incandescent bulbs. The looper, Trichoplusia ni (Hübner), to various host plants and latter were connected to a time-controlled dimming system host plant odours and to the floral compounds from night- providing 30 min transitions between the light regimes, to blooming jessamine, Cestrum nocturnum, has also been simulate dusk and dawn (H. armigera moths fly throughout reported (Landolt 1989; Heath et al. 1992). Zhu et al. (1993) the night, but simulating the natural transitions between day demonstrated the attractiveness of various flowering plants to and night could be important in initiating flight). Pupae were the cutworm, Agrotis ipsilon (Hufnagel), the armyworm, Pseu- sexed and upon emergence, moths were individually held in daletia unipuncta (Haworth) and the corn earworm, H. zea. 150 mL plastic containers and fed distilled water only until Additional work has documented the existence of volatile they were used in the olfactometer between 1 and 4 days of and non-volatile compounds which enhance oviposition. age. Unmated moths were used because targeting females Breeden et al. (1996) recorded oviposition stimulants for H. which had not laid eggs would be expected to produce the zea from the isolated acids and alkane wax fractions of various greatest reduction in oviposition. Moths were used once only Lycopersicon (Solanaceae) species. Jallow et al. (1999) dem- in the bioassays. onstrated that methanol, ethanol, acetone and pentane extracts from leaves, squares and flowers of different cotton genotypes Bioassay system influenced oviposition behaviour

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