Evaluation of a commercial Bacillus thuringiensis var. israelensis formulation for the control of chironomid midge larvae (Diptera: Chironomidae) in establishing rice crops in south-eastern Australia

A commercial formulation of Bacillus thuringiensis var. israelensis (B.t.i.) was evaluated for its potential to control chironomid midge larvae in newly sown rice crops in south-eastern Australia. Two replicated small-plot field trials were conducted using product application rates of 0.5-6 kg/ha. In trial 1 application rates between 2 and 6 kg product/ha all significantly (P < 0.05) reduced populations of target Chironominae/Orthocladiinae by between 71% and 93% over the 19 day post-treatment monitoring period. Trial 2 was conducted using lower application rates (0.5-2 kg product/ha) and only the 2 kg product/ha rate significantly (P < 0.05) reduced numbers of the target group (81% reduction) despite lower application rates resulting in target group suppression of 38-62%. Identification of larvae to species level from selected samples indicated that populations of Chironomus tepperi, the principal pest species that attacks the roots of rice seedlings, were reduced at all application rates; elimination of C. tepperi was achieved in trial 1 at an application rate of 2 kg/ha. Consistent with other studies, non-target Tanypodinae were not adversely affected by B.t.i., and in some treatments populations of Tanypodinae exceeded control levels by up to 73%. In the first trial, which was conducted under relatively high pest pressure, plant establishment was significantly (P < 0.05) increased (120-157%) by Vectobac® WDG application rates of 2-6 kg/ha. No significant increase in plant establishment relative to the controls was identified in the second trial, when pest pressure was substantially lower and minimal damage occurred in the control bays. Overall, our results demonstrate that B.t.i. may be an economically viable alternative to broad-spectrum synthetic pesticides for the control of phytophagous midge larvae in establishing rice crops where members of the Chironominae, the group most susceptible to B.t.i., are the principal species of concern. The high specificity of B.t.i. for nematoceran Diptera should lead to reduced impacts on non-target organisms.

Highlights► Vectobac® WDG is effective for controlling chironomine larvae in young rice crops. ► Optimal application rate under our trial conditions was between 1.25 and 2 kg/ha. ► Non-target tanypodine midge larvae were not adversely affected. ► Effective larval control improved crop establishment.