Chemical constituents of tropical woods and resistance to the invasive drywood termite Cryptotermes brevis

Abstract

Wood‐feeding, nesting and production of secondary reproductives are key determinant traits of invasive species of drywood termites, and the West Indian drywood termite Cryptotermes brevis (Walker) is one of their major examples of worldwide concern as pest species of structural lumber, furniture and other wood products. The problem and losses by this species are determined by the prevailing wood characteristics. However, despite the current widespread occurrence of this species in the tropics, except Asia, tropical wood resistance and underlying mechanisms of resistance against this termite are scarcely known. Nonetheless, wood hardness and particularly wood density were recently recognized as important underlying traits for C. brevis resistance in tropical woods, but the chemical wood constituents were not considered. Here, we assessed tropical wood resistance to the invasive termite species C. brevis and tested the relevance of their holocellulose, lignin and (total) extractive contents preventing termite infestation. Free‐choice and no‐choice tests were carried out in parallel with wood chemical characterization. Resistance to the West Indian termite varied with wood species in terms of both colonization and consumption, but only under free‐choice testing because without choice, no significant difference was detected among wood species. Regardless, none of these traits were significantly correlated with wood resistance to C. brevis. Therefore, wood physical resistance, particularly wood density, seems the main recognized determinant of tropical wood resistance against the West Indian drywood termite. The pattern of termite movement on the surface of soft, mid and hard wood was also consistent with this conclusion.

Do chewing cues from drywood termites mediate recruiting for wood colonization?

“…Our results supported the hypothesis that wood choice is an individual decision not associated with chewing cues. Perhaps though, this foraging decision is determined by the physical proprieties of the wood, which are the prominent drivers of feeding preference for drywood termite species (Cosme et al, 2018(Cosme et al, , 2020. These physical characteristics of wood also have significant life-history consequences for the organisms (Sih et al, 2004;Carere & Eens, 2005;R eale et al, 2007).…”

“…All bioassays and trials were carried out under controlled conditions of temperature (27 AE 3°C) and photoperiod (L0:D24 h, as drywood termites live inside wood in total darkness). In total 20 replicates were carried out for each bioassay, in which each replicate consisted of a group of insects (n = 10 pseudergates from the same stock colony) subjected to a free-choice test for 15 min, which was enough to start the colonization (i.e., termites clustering under one piece of wood) based on preliminary trials and previous studies (Cosme et al, 2018(Cosme et al, , 2020. Subsequently, both wooden blocks were isolated in plastic pots (500 ml).…”

“…The number of insects colonizing each wood-testing unit was recorded and monitored weekly through an Xray digital system (LX-60; Faxitron, Wheeling, IL, USA) to record colony survival, as the system allows recognition of placement and activity of the insects within the wooden block in successive visualizations. Furthermore, in order to record the total wood consumption in each trial arrangement at the end of the 220 days, the wood tunneling area (cm 2 ) was determined through radiography imaging (2D) using Image-Pro Plus v.4.5 (Media Cybernetics, Rockville, MD, USA), following methods previously reported by Cosme et al (2020). The initial tunneling of the previously infested wooden blocks were duly corrected in these subsequent determinations.…”

“…), which make them an interesting experimental model for communication studies. Wood size and quality are generally regarded as important foraging traits for drywood termites (Evans et al, 2005(Evans et al, , 2007(Evans et al, , 2011Inta et al, 2007a,b;Oberst et al, 2016Oberst et al, , 2018Cosme et al, 2018Cosme et al, , 2020. However, other, poorly studied factors may also be associated with wood preference.…”