Effect of Collection Month, Visible Light, and Air Movement on the Attraction of Male Agriotes obscurus L. (Coleoptera: Elateridae) Click Beetles to Female Sex Pheromone

Abstract

Elaterid female sex pheromone, while currently used for monitoring the adult life stage (click beetle), has only recently been explored as a potential management tool. Consequently, there is little understanding of how abiotic and biotic conditions influence the response of click beetles to the pheromone. We examined whether the response of male Agriotes obscurus L. (Coleoptera: Elateridae) beetles to a cellulose-based formulation of female sex pheromone ('pheromone granules') is influenced by air movement, presence of visible light, and month of beetle collection. In addition, we investigated the distance from which beetles were attracted to the pheromone granules. Click beetle response was determined by measuring movement parameters in free-walking arena experiments. The response to pheromone was not affected by the presence or absence of visible light. We found that beetles collected earlier in the season had increased activity and interaction with pheromone under moving air conditions, compared to beetles collected later. When controlling for storage time, we confirmed that individuals collected in May were less active than beetles collected in March and April. In the field, beetles were recaptured from up to 14 m away from a pheromone granule source, with over 50% being recovered within 4.4 h from a distance of 7 m or less. Understanding how abiotic and biotic factors affect pest response to pheromone can lead to more effective and novel uses of pheromone-based management strategies.

Keywords: attraction distance; behavior; chemical ecology; environmental factors; pest management.

Figure 1

Wind tunnel arena. Tunnel was constructed using 4-mm-thick Plexiglass. Corrugated plastic framed screens (S) were used to section off the middle to form an arena, the base of which was lined with brown dry sheathing paper, which was held down by 2-cm-wide, 3-mm-thick steel bars (SB) on all four sides. A band of blank or pheromone granules (G) were introduced 10 cm from the upwind end of the arena, and test beetles (B) were placed 10 cm from the downwind end of the tunnel at the start of trials. The tunnel was illuminated with two 23-W compact fluorescent lamp blubs (Daylight Mini Twister, Philips Lighting, Markham, ON, Canada) located on both sides of the arena (LB), which were diffused with a layer of foam (FM). At one end of the tunnel, a 52 cm × 52 cm box fan (F) was used to drive wind through activated charcoal (AC).

Figure 2

Impact of pheromone and air movement on male Agriotes obscurus click beetles. (A) LS mean (±SE) walking speed; (B) time to first contact with pheromone band; and (C) frequency of contacts with band. April: N = 87; May: N = 82. Either side of the violin plot shows the distribution of the data via a probability density, with wider sections indicating values occurring at higher frequency. *** represent significance p < 0.05, as assessed by contrasts in a generalized linear model. Letters represent significance at p < 0.05 (Tukey’s HSD).

Figure 3

Impact of collection month on male Agriotes obscurus click beetle activity in response to pheromone treatment for beetles. Total beetles tested (number of batches with 1–5 beetles in a batch/replicate): March: 220 (44); April: 188 (47); May: 195 (48). Activity is depicted by mean (±SE) (A) walking speed and (B) movement duration. Letters represent significance at p < 0.05, as assessed by Tukey’s HSD.

Figure 4

Mean proportion (±SE) of Agriotes obscurus beetles recovered after release from 1, 3, 7, and 14 m away from a band of blank or pheromone granules. N = 4 per treatment. The final model is % recovered = 4.0045 (pheromone) − 0.693 (distance) + 0.4396 (release side) +/− 0.4513(distance × pheromone) − 1.480.