Pot trial screening of alternative chemical and biological products against larvae of Schizonycha affinis (Coleoptera: Scarabaeidae) on wattle and eucalypt seedlings

Sivparsad BJ, Morris A
Publication Type
Technical Note
Publication Year

White grubs (Scarabaeidae larvae) can contribute to serious transplant mortality immediately following re-establishment. Synthetic insecticidal treatments of deltamethrin and imidacloprid are currently used in the control of white grub and other soil-borne insects of commercial forest tree species. However, the use of these insecticides has been deemed highly hazardous and is regulated by the Forest Stewardship Council (FSC). Therefore, there is an immediate need to find effective alternative products for the control of white grubs. A pot trial was undertaken to assess the effectiveness of alternative chemical and biological products to control white grub feeding on Acacia mearnsii and Eucalyptus grandis seedling roots. Six biological options (Beauveria bassiana, Beauveria brongniartii, Bacillus thuringiensis subspecies kurstaki, azadirachtin, diatomaceous earth and potassium silicate), five chemical control options (imidacloprid granules, clothianidin, imidacloprid + clothianidin tablets, imidacloprid + clothianidin + metalaxyl tablets and imidacloprid + Trichoderma asperellum tablets) and three insecticides with known efficacy (deltamethrin, imidacloprid liquid and imidacloprid tablets) were evaluated for the control of Schizonycha affinis on A. mearnsii and E. grandis seedlings. All treatment combinations were compared to two control treatments; a positive control (white grub present, no chemical product), and a negative control (no white grub present, no chemical product). For A. mearnsii seedlings, area under disease progress curve (AUDPC) values were calculated based on periodic evaluations of percentage mortality/ wilting. Seedlings of A. mearnsii and E. grandis treated with imidacloprid tablets and imidacloprid + clothianidin tablets showed a significant increase in total biomass when compared to the positive control. Treatment with imidacloprid tablets and liquid produced a significant reduction in percentage mortality and AUDPC for A. mearnsii seedlings. Biological products containing B. bassiana and B. thuringiensis subspecies kurstaki did not reduce white grub damage of seedlings. Conversely, treatments of azadirachtin, potassium silicate and B. brongniartii increased total biomass and could provide viable alternatives for control of white grubs. Results indicate that potential alternative white grub control options exist, and further pot and field trial evaluations are warranted to confirm product recommendations.