Spectral sensitivity of click beetles (Coleoptera: Elateridae) and their responses to light stimuli in laboratory and field experiments.

With increasingly fewer insecticides registered to control the larvae of pest click beetles (Coleoptera: Elateridae), integrative beetle management, including pheromone- and light-based trapping of adult beetles, must be explored as an alternative strategy. Here, we analyzed the spectral sensitivity and color preference of 9 elaterids across 6 genera in electrophysiological recordings and in behavioral bioassays. In electroretinogram recordings (ERGs), dark-adapted beetles were exposed to narrow wavebands of light in 10-nm increments from 330 to 650 nm. All beetles proved most sensitive to green (515-538 nm) and ultraviolet (UV) light (~360 nm). In 4-choice bioassay arenas with 3 light emitting diodes (LEDs; green [525 nm], blue [470 nm], red [655 nm]) and a dark control as test stimuli, beetles discriminated between test stimuli, being preferentially attracted to green and blue LEDs. In field experiments, Vernon pitfall traps fitted with a green, blue or white LED captured significantly more male and female Agriotes lineatus and A. obscurus than dark control traps. When traps were baited with green or blue LEDs at light intensities that differed by 10-fold, the traps baited with higher light intensity lures captured numerically more beetles but trap catch data in accordance with light intensity did not differ statistically. Light-based trapping may be a viable tool for monitoring elaterid species known not to have pheromones.

Seasonal and Diel Communication Periods of Sympatric Pest Limonius Click Beetle Species (Coleoptera: Elateridae) in Western Canada.

In western North America, sympatric Limonius click beetle species produce limoniic acid [(E)-4-ethyloct-4-enoic acid] as a sex pheromone component (L. canus (LeConte), L. californicus (Mannerheim)) or respond to it as a sex attractant (L. infuscatus (Motschulsky)). We tested the hypothesis that these three congeners maintain species-specificity of sexual communication through nonoverlapping seasonal occurrence and/or contrasting diel periodicity of sexual communication. Using capture times of beetles in pheromone-baited traps as a proxy for sexual communication periods, our data show that L. canus and L. californicus have seasonally distinct communication periods. Most L. canus males (>90%) were captured in April and most L. californicus males (>95%) were captured in May/June/July. As almost exclusively L. infuscatus males were captured in two separate 24-hr trapping studies, with data recordings every hour, it remains inconclusive whether the three Limonius congeners communicate at different times of the day. Males of L. infuscatus responded to pheromone lures only during daytime hours and during the warmest period each day. Captures of L. infuscatus overlapping with those of L. canus in April and those of L. californicus in May/June imply the presence of reproductive isolating mechanisms other than seasonal separation of sexual communication periods.

Identification of the Major Sex Pheromone Component of the Click Beetle Agriotes ferrugineipennis.

Synthetic sex pheromone lures are useful tools to monitor and control populations of adult click beetles (Coleoptera: Elateridae). However, sex pheromones for Agriotes click beetle species native to North America have yet to be identified. Here we report the identification and field testing of the sex pheromone of Agriotes ferrugineipennis. Headspace volatiles from female beetles were collected on Porapak Q, and aliquots of Porapak extract were analyzed by gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry. 7-Methyloctyl 7-methyloctanoate (7Me7Me) emitted by females was more abundant and elicited much stronger responses from male antennae than the aldehydes octanal and nonanal and the ketone 6,10,14-trimethyl-2-pentadecanone. In a field experiment, captures of A. ferrugineipennis males in traps baited with candidate pheromone components exceeded those of unbaited control traps, on average by nearly 1,200 times. Neither the ketone nor the aldehydes as lure constituents appeared to alter captures of males in 7Me7Me-baited traps. We conclude that 7Me7Me is the major, and possibly the only, sex attractant pheromone component of female A. ferrugineipennis.