Control of painted lady caterpillars, Vanessa cardui L. (Lep., Nymphalidae), on borage by Bacillus thuringiensis var. kurstaki
1993
Miranpuri, G.S. (Saskatchewan Univ., Saskatoon (Canada). Dept. of Applied Microbiology and Food Science. Bioinsecticide Research Lab.) | Bidochka, M.J. | Khachatourians, G.G.
In the summer of 1991 in the Saskatoon and surrounding area, borage (Borago officinalis), a speciality crop of Saskatchewan, was found heavily infested by Painted Lady caterpillar, Vanessa cardui L. Laboratory and field trials with Bacillus thuringiensis var. kurstaki Berliner (Btk; Dipel wettable powder) at 0.625 g/l showed efficacy against different developmental stages of Painted Lady caterpillars. Treatment effects were assessed in terms of arrested feeding of the larvae, survival of caterpillars of different size cohorts (I, II, III according to size distribution), pupae and adult emergence. Efficacy against caterpillars was assessed using four methods of treatment: 1. individual or; 2. a group of caterpillars in the laboratory; 3. caterpillars in the field contained with a mesh enclosure; and 4. field plot treatment. In laboratory bioassays with borage leaf discs or while plants treated with Btk, the mortality of the smallest (below 1.25 cm, I) caterpillars was higher than that of II (below 2 cm) or III (above 2 cm) caterpillars. Whereas untreated borage leaf discs fed to caterpillars were usually totally consumed within 2-4 h, 95% Btk-treated discs were left uneaten even after 24 h. No adult emergence was observed from the pupae collected from caterpillars which were fed Btk-treated discs. Field application of Btk on borage resulted in a 4 to 8.5-fold decline in the Painted Lady caterpillar population from 8 to 15 days post treatment. As borage plant seeds are a rich source for gammalinolinic acid which is used therapeutically for treatment of essential fatty acid deficiency in humans, it cannot be sprayed with chemical pesticides when fully blossomed. We therefore conclude that the use of Btk offers an acceptable, effective non-chemical method to control Painted Lady caterpillars
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