Insect predators play a critical role in food web dynamics and pest management (Polis and Strong 1996; Tipping et al. 1999; De Clercq et al. 2003). Often, the focus of predators’ role in trophic interactions is on the consumptive effect predators have on prey. Another way predators interact with prey is by eliciting non-consumptive responses that increase preys’ chances of survival (Sih 1980; Lima and Dill 1990; Werner and Peacor 2003). Non-consumptive effects are often mediated via sensory cues (Weissburg et al., 2014), however little work has been done to understand how predator development affects the delivery of cues. Knowing this type of information will improve our ability to make predictions about the effects of predators on prey. Olfaction is one of the most heavily relied-upon sensory modality used by insect predators and prey. Pentatomids, aptly named stink bugs, produce a diverse array of chemical compounds and the use of chemical communication is assumed to be especially pronounced in this group.
The spined soldier bug (Podisus maculiventris), is a common omnivorous stink bug that is distributed across North America (Legaspi and Legaspi 2007). It is a voracious consumer of numerous insect species, including agricultural pests, and has been released throughout its native range for augmentative biological control, and in Europe for inoculative biological control (Biever, Chauvin, 1992; Hough-Goldstein & McPherson, 1996). A wealth of research has been conducted on this stink bug species to determine how to use it effectively for biological control (Tipping et al. 1999), with a particular focus on its chemical ecology. This species produces numerous volatile chemicals that are released via a series of exocrine glands (Aflitto & Thaler, 2020; Aldrich, 1988; Hermann & Thaler, 2014; Sant’Ana, Bruni, Abdul-Baki, & Aldrich, 1997). The dorsal abdominal gland (DAG) is of specific interest to chemical ecologist as adult male bugs can release large amounts (> 1 mg) of pheromone from it into their surrounding environment (Aldrich, 1995). This strong olfactory cue has long intrigued chemical ecologists, raising questions regarding its importance in driving inter- and intraspecific interactions. Note that for the purposes of this paper, we refer to the odors released from the DAG that are used for intraspecies communication as pheromones, and when referring to the perception of those same compounds by other organisms we refer to them as semiochemicals. Recent work has highlighted the importance of interspecific detection of the DAG semiochemical. For example, Aflitto & Thaler, 2020, 2021, and Hermann & Thaler, 2014, demonstrated that Colorado potato beetles (Leptinotarsa decemlineata (Say)), an economically important crop pest of solanaceous plants, consume less plant tissue in the presence of DAG semiochemicals. Adding to the intrigue is the fact that many other organisms are known to have receptors that detect one or more of the compounds released from the DAG blend, including certain plants.
Here, we investigate four factors that may influence the presence of DAG semiochemical in the environment: 1) adult male age, 2) sexual maturity, 3) time of day, and 4) interactions with conspecifics. Emissions from the DAG are controlled by the opening and closing of an ostiole located on the abdominal dorsum of bugs. However, the factors that elicit releases from the gland are not well described. More evidence linking the DAG development with other physiological processes such as sexual maturation may uncover a more nuanced use of this semiochemical cue and contribute to a greater understanding of the ecological effects of this source of chemical information in a system. Ontogentic changes in P. maculiventris gland development from the immature to adult stage has been well studied (Aldrich et al., 1984b). However, less is known about changes in gland volume and composition that occur during the adult stage in P. maculiventris, and more broadly Pentatomids (see Mcbrien et al., 2001; Cribb et al., 2006). To better understand how adult age affects gland development and emissions, we investigated how the amount and composition of DAG chemicals change from the point of adult male eclosion through sexual maturity (ca. 7 d) and into middle age (14 d old). To learn more about the potential congruencies between gland development and sexual maturity, we measured the size of DAGs of these three age classes, removed, extracted, and analyzed their contents. We then quantified the number of sperm (our proxy for sexual maturity) in their seminal vesicles. Finally, to understand the behavioral and diurnal conditions that elicit the release from the DAG, we used the same age classes mentioned above, paired a male bug with either another male or a female, and measured the total number of volatile chemical releases over 24 h.