COMMUNITY ECOLOGY AND DAMAGE CHARACTERISTICS OF WOOD-BORING BOSTRICHID BEETLES IN STORED TIMBER

Abstract

Background: Bostrychid beetles (Coleoptera: Bostrichidae) have a worldwide distribution but are predominantly found in tropical and arid regions. One of the most characteristic signs of infestation is the perfectly circular exit holes created by adults at emergence, with diameters varying by species. The boring activity of larvae causes damage in stems, branches, and twigs of dead, damaged, or stressed hosts, and tunnelling through host tissues leads to extensive frass-filled galleries. An experiment was conducted to document the population dynamics of wood-boring bostrychid beetles collected from different wood yards at Mettupalayam, Tamil Nadu, India. Objective: To document the population dynamics, species diversity, and damage assessment of wood-boring bostrychid beetles in commercial wood depots Methods: Five commercial timber depots located in different areas of Mettupalayam were purposively selected as study sites. Five commercially important wood species, known locally to be susceptible to wood borer attack and widely stocked across the selected depots, were chosen. At each timber depot, infested billets or planks of the five target wood species were visually identified. From each site, multiple infested pieces per wood species were randomly selected from different positions within the stacks (top, middle and bottom layers; inner versus outer stacks) to minimize location bias within depots. Results: A total of 455 adult beetles belonging to four genera and two families (Bostrichidae and Scolytinae) were recovered from the emergence containers. Of the 455 beetles recovered, 319 individuals (70.11%) were identified as wood-boring beetles of the family Bostrichidae, comprising species of Sinoxylon, Lyctus, and Dinoderus (Table 1). The remaining beetles included Scolytus sp. (6 individuals) and unidentified beetles that did not belong to Bostrichidae. Within the total assemblage, four genera of wood-boring beetles were identified. Wood-boring beetles recovered from wood depots between September 2019 and February 2020. Analysis of exit hole diameters across all five wood species revealed a highly consistent pattern: the 1.1–2.0 mm size class contained the greatest number of exit holes in every wood species, followed by the ≤ 1.0 mm class. The highest beetle emergence was recorded during weeks 8 and 10 of the observation period. Maximum emergence of 6 individuals recorded in week 10, recovered specifically from bamboo substrates. Conclusion: It was demonstrated that wood-boring beetle assemblages in commercial timber depots at Mettupalayam are overwhelmingly dominated by the family Bostrichidae, which contributed 65.00–74.66% of all beetles recovered across the five study sites. The consistently high proportional representation of Bostrichidae across all five depots in the present study regardless of differences in depot size, stacking methods, or timber volume. The dominance of the 1.1–2.0 mm exit hole size class across all five wood species, followed by the ≤ 1.0 mm class, has important diagnostic significance. Although the overall beetle fauna was broadly similar across the five depots, significant differences in exit hole density among sites were observed for some wood species, particularly silver oak and eucalyptus. This spatial variation suggests that local depot conditions modulate infestation intensity even when the underlying pest species pool is similar.