Mercury bioaccumulation in dragonflies (Odonata: Anisoptera): examination of life stages and body regions.

Dragonflies (Odonata: Anisoptera) are an important component of both aquatic and terrestrial food webs and are vectors for methylmercury (MeHg) biomagnification. Variations in mercury content with life stage and body regions may affect the relative transfer of mercury to aquatic or terrestrial food webs; however, there has been little research on this subject. Also, little is known about mercury bioaccumulation in different body regions of dragonflies. To address these knowledge gaps, dragonfly naiads, adults, and exuviae were collected at 2 lakes in Kejimkujik National Park, Nova Scotia, Canada, and mercury concentrations in different life stages and body regions were quantified. Mean whole body concentrations of MeHg were substantial in naiads (232 ± 112 ng g(-1) dry wt, n = 66), emerging adults (236 ± 50 ng g(-1) dry wt, n = 10), and mature adults (231 ± 74 ng g(-1) dry wt, n = 20). Mean MeHg concentrations in exuviae (5.6 ± 4.3 ng g(-1), n = 32) were 40-fold lower than in naiads and adults. Emerging adults had 2-fold to 2.5-fold higher Hg(II) concentrations than naiads, mature adults, and exuviae. In body regions of both naiads and adults, some abdomens contained significantly higher concentrations of Hg(II) than heads or thoraces, and this trend was consistent across families. Across families, Aeshnidae had significantly higher concentrations of MeHg and total Hg than Gomphidae and Libellulidae, but not higher than Cordulidae. The Hg(II) concentrations were lower in Aeshnidae and Libellulidae than in Gomphidae and Cordulidae. Shedding of exuviae presents a possible mechanism for mercury detoxification, but mercury concentrations and burdens in exuviae are low in comparison with naiads and adults. Dragonfly adults retain a high potential for transferring substantial amounts of MeHg to their predators.

Phenology of semiochemical-mediated host foraging by the western boxelder bug, Boisea rubrolineata, an aposematic seed predator.

The western boxelder bug (BEB), Boisea rubrolineata (Heteroptera: Rhopalidae), is a specialist herbivore of boxelder trees, Acer negundo. We tested the hypothesis that BEBs use semiochemicals to locate host trees. Headspace volatiles from trees bearing staminate inflorescences ("staminate trees") and from trees bearing pistillate inflorescences ("pistillate trees") were collected throughout the season and bioassayed in Y-tube olfactometer experiments. Headspace extracts of early-season, pollen-bearing staminate trees and midseason pistillate trees with mature samaras (seed pods) attracted female and male BEBs. By using coupled gas chromatographic-electroantennographic detection and gas chromatography-mass spectrometry, we identified and tested a five-component synthetic blend of candidate semiochemicals (hexanol, pentyl acetate, phenylacetonitrile, 2-phenethyl acetate, and trans-nerolidol). This blend attracted females, males, and fifth-instar nymphs. Phenylacetonitrile by itself was as attractive as the five-component blend to both adults and nymphs. By responding to phenylacetonitrile emitted by pollen-bearing staminate trees and pistillate trees with maturing seeds, BEBs appear to track and exploit the availability of nutrient-rich food sources, suggesting that the bugs' reproductive ecology is synchronized to the phenology of their host boxelder tree.