No abstract

Tetrastichus planipennisi Yang is a gregarious larval endoparasitoid native to China and has been introduced to the United States since 2007 for classical biological control of the invasive emerald ash borer, Agrilus planipennis Fairmaire, an exotic beetle responsible for widespread ash mortality. Between 2007-2010, T. planipennisi adults (3,311-4,597 females and approximately 1,500 males per site) were released into each of six forest sites in three counties (Ingham, Gratiot, and Shiawassee) of southern Michigan. By the fall of 2012, the proportion of sampled trees with one or more broods of T. planipennisi increased to 92 and 83% in the parasitoid-release and control plots, respectively, from 33 and 4% in the first year after parasitoid releases (2009 fall for Ingham county sites and 2010 for other sites). Similarly, the mean number of T. planipennisi broods observed from sampled trees increased from less than one brood per tree in the first year after parasitoid releases to 2.46 (at control plots) to 3.08 (at release plots) broods by the fall of 2012. The rates of emerald ash borer larval parasitism by T. planipennisi also increased from 1.2% in the first year after parasitoid releases to 21.2% in the parasitoid-release plots, and from 0.2 to 12.8% for the control plots by the fall of 2012. These results demonstrate that T. planipennisi is established in southern Michigan and that its populations are increasing and expanding. This suggests that T. planipennisi will likely play a critical role in suppressing emerald ash borer populations in Michigan.

We examined various methods of trapping emerald ash borers (EAB), Agrilus planipennis Fairmaire, using solely visual cues based on previous work that has documented the importance of visual cues in EAB mate location. Here, we give the results of two of these methods, coloured sticky cards (yellow or blue), or live ash leaves covered with spray‐on adhesive to which dead male EAB visual lures had been pinned. Feral male beetles were captured effectively on the sticky traps made from dead male EAB on ash leaves. These sticky‐leaf‐traps captured more male EAB when deployed in high‐population density areas than low‐density areas, but did capture EAB even at lower population densities. More feral males were captured on these traps when they were placed higher in the trees, regardless of the population density of EAB. Very few feral female EAB were captured using the sticky‐leaf‐traps. This novel method of EAB trapping may allow ‘real‐time’ population detection and monitoring of EAB adults during the active flight period rather than locating larval galleries during the autumn and winter after adult flight and attack. Feral male beetles were also captured using standard yellow‐ or blue‐coloured sticky cards to which male EAB had been affixed with adhesive; however, this type of trap was much less effective overall than using the sticky‐leaf‐traps. Furthermore, Agrilus cyanescens, a species similar in colour to EAB but smaller in size, showed a strong response to blue‐coloured sticky traps to which dead male EAB had been affixed with adhesive, suggesting a general use of visual cues in the mating systems of some of the other Buprestidae as well.

The cuticular hydrocarbon profiles of emerald ash borers, Agrilus planipennis, were examined to determine if there are differences in these compounds between the sexes. We also assessed feral male EAB in the field for behavioral changes based on the application of a female-specific compound to dead, solvent-washed beetles. Males in the field spent significantly more time attempting copulation with dead, pinned female beetles coated with a three-beetle-equivalent dose of 3-methyltricosane than with solvent-washed beetles or those coated in 3-methyltricosane at lower concentrations. Males in the field spent the most time investigating pinned dead, unwashed female beetles. In the laboratory, sexually mature males were presented with one of several mixtures applied in hexane to filter paper disks or to the elytra of dead female beetles first washed in solvent. Male EAB also spent more time investigating dead beetles treated with solution applications that contained 3-methyltricosane than dead beetles and filter paper disks treated with male body wash or a straight-chain hydrocarbon not found on the cuticle of EAB.

BackgroundArthropods have received much attention as a model for studying opsin evolution in invertebrates. Yet, relatively few studies have investigated the diversity of opsin proteins that underlie spectral sensitivity of the visual pigments within the diverse beetles (Insecta: Coleoptera). Previous work has demonstrated that beetles appear to lack the short-wavelength-sensitive (SWS) opsin class that typically confers sensitivity to the “blue” region of the light spectrum. However, this is contrary to established physiological data in a number of Coleoptera. To explore potential adaptations at the molecular level that may compensate for the loss of the SWS opsin, we carried out an exploration of the opsin proteins within a group of beetles (Buprestidae) where short-wave sensitivity has been demonstrated. RNA-seq data were generated to identify opsin proteins from nine taxa comprising six buprestid species (including three male/female pairs) across four subfamilies. Structural analyses of recovered opsins were conducted and compared to opsin sequences in other insects across the main opsin classes—ultraviolet, short-wavelength, and long-wavelength.ResultsAll nine buprestids were found to express two opsin copies in each of the ultraviolet and long-wavelength classes, contrary to the single copies recovered in all other molecular studies of adult beetle opsin expression. No SWS opsin class was recovered. Furthermore, the male Agrilus planipennis (emerald ash borer—EAB) expressed a third LWS opsin at low levels that is presumed to be a larval copy. Subsequent homology and structural analyses identified multiple amino acid substitutions in the UVS and LWS copies that could confer short-wavelength sensitivity.ConclusionsThis work is the first to compare expressed opsin genes against known electrophysiological data that demonstrate multiple peak sensitivities in Coleoptera. We report the first instance of opsin duplication in adult beetles, which occurs in both the UVS and LWS opsin classes. Through structural comparisons of known insect opsins, we suggest that opsin duplication and amino acid variation within the chromophore binding pocket explains sensitivity in the short-wavelength portion of the visible light spectrum in these species. These findings are the first to reveal molecular complexity of the color vision system within beetles.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0674-4) contains supplementary material, which is available to authorized users.