Evaluating the potential of long lasting insecticide-incorporated nets and Beauvaria bassiana for control of the tropical nut borer, Hypothenemus obscurus

The tropical nut borer, Hypothenemus obscurus (F.) (Coleoptera: Curculionidae: Scolytinae), is one of the biggest threats to macadamia production in Hawaii, accounting for 5.8% of the total loss of macadamia nuts on the Island. Damage by H. obscurus is visible as small holes through the husk, shell, and kernel. Here, under laboratory conditions (25±1 °C, 60-65% RH, 12:12 L:D), we tested the efficacy of two potential integrated pest management (IPM) tools: (1) Long-Lasting Insecticide-Incorporated Netting (LLINs) and (2) An entomopathogen; Beauvaria bassiana in a commercially available product, BotaniGard®22WP. In the LLINs bioassays, 20 adult beetles were tested at three different exposure times: 1, 6, 12, and 24 hours to LLINs and a control (without insecticides) netting with 11 replicates each. Mortality and sub-lethal effect data (death and morbidity) were recorded after 24, 48, and 120 hours. In the B. bassiana bioassays three concentrations or treatments: 0.5, 1, and 2 times the recommended dosage, were applied to 20 beetles and replicated 10 times with controls. Mortality and sublethal effect data, previously mentioned in the LLINs bioassay, were recorded every 5 days, and five checks were made in total. The results showed a significant increase in H. obscurus mortality when exposed to LLINs. Similarly, the application of BotaniGard®22WP to H. obscurus had significant effects on H. obscurus, causing significantly high mortality with increasing concentrations. Therefore, LLINS and B. bassiana may be considered for field IPM of H. obscurus in Hawaii to reduce its pressure and damage.