COS 89-4
The flight phenology of a depressariid moth: Do adults respond to UV lights and to host plant volatiles?
Knowledge of the flight period of insects can be of great importance to develop models that accurately forecast insect phenology. The prediction is even more crucial for species overwintering as adults, as observed in some microlepidopteran pests. Adults emerging in the spring can be expected to arise shortly after temperatures increase. The caraway moth, Depressaria daucella, is a common holarctic herbivore that feeds on wild and cultivated Apiaceae. The scarce literature suggests that Depressarinae moths are seldom attracted by UV lights but evidence is missing for D. daucella. Until the sex pheromone can be identified, host plant odors could be of interest to determine D. daucella flight period or to understand host plant selection. Yet, no study has investigated how adults respond to plant volatiles, such as ocimene, R-(+)-limonene and carvone. In this work, we studied the flight period of D. daucella within caraway fields located in Southern Finland. We investigated D. daucella responses to delta sticky traps baited with putative attractants: Z-3-decenyl acetate (D) - an attractant for Depressaria depressana, ocimene (O), R-(+)-limonene (L), carvone (C) and L+C. We also compared two types of traps using UV "white" or "blue" (UVA combined to different peaks of visible light).
Results/Conclusions
Our results suggest that trapping D. daucella with UV lights is the most efficient technique, but the method seems to be useful only for adults emerging from winter. Indeed, all individuals were captured in the spring, while light traps recording during the summer failed to capture adult moths. Moreover, the pattern of captures observed with light traps in 2013 revealed a narrow flight period occurring in mid-May, with > 95% of insects (N = 279 individuals) captured in two weeks, and 45% captured in one night. Although our data are preliminary, no major differences between white and blue lights were observed. The largest variation of moth catches occurred between fields which were separated by at least 10 km. Conversely, delta traps baited with semiochemicals did not attract more moths than the unbaited control, and traps baited with R-(+)-limonene actually tended to capture less adults than the control. In a previous study, we showed that limonene can repel D. daucella larvae. Overall, this study suggests that UV lights could be useful to determine adult flight period and may enable to assess the relative abundance of D. daucella in sites distant from > 10 km. R-(+)-limonene could act as a potential repellent.