Differences in insect anatomy may affect tolerance to the fumigant ethanedinitrile

Ethanedinitrile (EDN) is a potential alternative fumigant to methyl bromide for the phytosanitary treatment of timber and logs. Previously, adult golden-haired bark beetles (Hylurgus ligniperda) have shown high rates of tolerance to EDN, while all life stages of burnt-pine longhorn beetles (Arhopalus ferus) were highly susceptible. These results suggest that the fumigant mode of action might be species-specific and more complex than previously thought. Therefore, the anatomy of these beetles was examined to investigate potential differences in EDN toxicity related to these insect traits. The mesothoracic and fourth abdominal cuticles of 20 individuals were measured and compared across the two species. Spiracle sizes of 20 adult insects were also measured and compared across and within species. Of the two species, A. ferus had the thicker dorsal thoracic and abdominal cuticle. Adults of A. ferus had also the larger total spiracle area. These results provide important information to help explain the observed differences in EDN tolerance across the two species. Further work will test the main route of entry of EDN into the bodies of target insects and additional effects on EDN on insect behaviour.