Quantifying the thermal tolerance of wood borers and bark beetles for the development of Joule heating as a novel phytosanitary treatment of pine logs

Abstract

Industrial roundwood is an important commodity with global trade of 125 million m3 in 2016. Fumigation is the main phytosanitary treatment for bulk wood commodities. Joule heating is a potential alternative phytosanitary treatment for export Pinus radiata D. Don (Pinaceae) logs, but its effectiveness against insects has not yet been confirmed experimentally. To define treatment parameters for Joule heating, we quantified the thermal tolerance of two forest insects, Hylurgus ligniperda (Fabricius) (Scolytinae) and Arhopalus ferus (Mulsant) (Cerambycidae) that are potentially present on P. radiata logs. Heat was applied using dry bath heat blocks to life stages present when phytosanitary treatments are applied. Arhopalus ferus eggs were the most heat-tolerant life stage with decreasing tolerance at 30 min of H. ligniperda adults > H. ligniperda larvae > A. ferus adults, > A. ferus larvae, H. ligniperda eggs, and H. ligniperda pupae. Additional testing of A. ferus eggs (in dry and humidified environments) determined that an upper LT99.99 with 95% confidence of 55.6 °C applied for 30-min controlled A. ferus and hence all other life stages. This is within the range of published studies of other bark- and wood-boring insects, which are reviewed. The LT99.99 and wood-borer biology are discussed in the context of Joule heating as a potential phytosanitary treatment for bulk wood exports. Joule heating of 32 test logs (3.3 m long) demonstrated temperatures exceeding 60 °C for at least 60 min. Ten logs infested with H. ligniperda were Joule-heated to the same profile, resulting in 100% mortality of adults and larvae. Our results are consistent with current ISPM 15 treatment parameters and show that Joule heating is an effective, non-chemical, alternative option to fumigation for quarantine pest control.