Physical contact, volatiles, and acoustic signals contribute to monogamy in an invasive aggregating bark beetle

Abstract

The behavioral strategies and mechanisms by which some insects maintain monogamous mating systems are not well understood. We investigated the mating system of the bark beetle Dendroctonus valens, and identified several contributing mechanisms. Field and laboratory observations suggest the adults commonly form permanent bonds during host colonization. Moreover, it showed mated females that remained paired with males produced more offspring than mated females that were alone in galleries. In bioassays, a second female commonly entered a gallery constructed by a prior female. Videos show she commonly reached the location of the first female, but they did not engage in actual fighting. Rather, the second female typically departs to form her own gallery. Acoustic signaling likewise does not appear to influence female-female encounters, based on controlled muting experiments. Instead, the intruder appears to perceive the resident's presence by physical contact. Both acoustic signals and volatiles released by females during gallery constructing were shown to attract males. After a male joined a female in a gallery, the male-produced aggressive sounds, which were shown by playback to deter other males from entering the gallery. Unlike female-female interactions, resident males use their head and rear to push intruders out of galleries. Additionally, volatiles released by males during feeding repelled intruding males, discouraging them from entering the gallery. Males also construct plugs that block the entrance, which may prevent subsequent males and predators from entering the gallery. Thus, D. valens has evolved multifaceted mechanisms contributing to single pairings that confer benefits to both sexes.

Fighting and aggressive sound determines larger male to win male‐male competition in a bark beetle

“…As D. valens is monogamous (Liu et al ., 2020), it is critical for a male to attain a female partner to have offspring and face intense competition since they attack in aggregations (Liu et al ., 2008). In our previous studies, we observed that the winning male enters the gallery made by the female and the loser male stays at the entrance of the gallery (Liu et al ., 2020). The male normally enters the female's gallery mostly within 1 h (Liu et al ., 2006).…”

“…S1B and C), were simultaneously introduced into the pre‐drilled hole and resealed with iron mesh (20 replicates). As D. valens is monogamous (Liu et al ., 2020), it is critical for a male to attain a female partner to have offspring and face intense competition since they attack in aggregations (Liu et al ., 2008). In our previous studies, we observed that the winning male enters the gallery made by the female and the loser male stays at the entrance of the gallery (Liu et al ., 2020).…”

“…In its native ranges, only one or a few females usually establish galleries within a host, but in China, it commonly attacks trees in dense aggregations (Liu et al ., 2008; Aukema et al ., 2010; Chen, 2012; Liu et al ., 2013), as evidenced by observations that up to 162 beetles may attack a small 700 mm tall stump over a 2‐day period (Chen, 2012). Moreover, similar to other Dendroctonus species, D. valens is monogamous (Wood, 1982; Liu et al ., 2006; Latty & Reid, 2010; Owen et al ., 2010; Liu et al ., 2020) and females initiate attack and construct galleries before being joined by a mate, thus making females a critical resource for male (Liu et al ., 2006) . This indicates males may face intense male‐male competition on the bark surface or inside the galleries.…”

“…S1B and C), which provides an excellent opportunity to explore male‐male competition related to body size. Moreover, males produce “aggressive/rivalry” sounds as a territorial function, which may be involved in male‐male competition (Liu et al ., 2020).…”

Pinyon Engraver Beetle Acoustics: Stridulation Apparatus, Sound Production and Behavioral Response to Vibroacoustic Treatments in Logs

“…Interestingly, the non-pioneering sex typically has welldeveloped stridulatory structures [11,12] and will stridulate (i.e., produce sounds/vibrations) when arriving near or inside the gallery of a pioneer's entry hole [13,14]. Airborne sounds and stridulatory structures of many bark beetles have been described [13,[15][16][17][18][19] and the ecological roles of stridulation in some bark beetle species are well studied [18,[20][21][22][23][24][25][26][27]. Interestingly, Insects 2021, 12, 496 2 of 19 bark beetle stridulation sounds influence pheromone production and composition of bark beetle partners within the tree.…”