Olfactory responses of the multicoloured asian lady beetle (Harmonia axyridis) to vineyard volatiles
The introduced biological control agent 'Harmonia axyridis' (Coleoptera: Coccinellidae) has attained pest status in North America as its presence in vineyards during harvest may compromise the quality of the resulting wine. The objective of this thesis was to identify both attractants and repellents for 'H. axyridis', in order to manipulate beetle behaviour and presence in vineyards. The antennal response of 'H. axyridis' to grape ('Vitis vinifera' var. Riesling) volatile compounds was recorded by gas chromatographic-electroantennographic detection (GC-EAD). Compounds that consistently elicited antennal activity were hexanol, linalool, nonanal, and [beta]-caryophyllene. In a four-arm olfactometer, 'H. axyridis' were significantly attracted towards [beta]-caryophyllene but displayed no behavioural response to hexanol, linalool, nor nonanal. In a vineyard, sticky traps baited with antennally active compounds, alone and in combination, failed to attract beetles. In a four-arm olfactometer, ' H. axyridis' displayed a variable response to grapes during ripening, but there is some evidence that beetles prefer undamaged grapes over damaged grapes. The concentration of [beta]-caryophyllene was relatively constant throughout the ripening period and did not differ between damaged and undamaged grapes. In contrast concentrations of hexanol, linalool, and nonanal changed during berry ripening. The response of 'H. axyridis' to undamaged grapes suggests that beetles may be attracted to vineyards by olfactory cues; however, their response to antennally active grape compounds does not support this result. Sulphur dioxide, in the form of potassium metabisulfite (KMS), was determined to be an effective repellent against 'H. axyridis'. In a Y-tube olfactometer, 'H. axyridis' spent significantly less time in the KMS arm (2.5, 5, and 10 g/L) than in the control arm. When sprayed in a vineyard, KMS at 10 g/L consistently reduced the number of ' H. axyridis' on grape vines 24 h after application. Future research should establish the duration of KMS repellency and the effect of environmental conditions on repellency. Future studies should continue to examine the olfactory response of'H. axyridis' to grapes, as the composition of volatile compounds can vary greatly depending on the variety, environmental conditions, and cultural practices.