Interaction of mulch and Bacillus thuringiensis subsp tenebrionis on Colorado potato beetle (Coleoptera: Chrysomelidae) populations and damage in potato

The use of straw mulch and no-mulch, a synthetic pyrethroid (esfenvalerate, Asana XL) and a bioinsecticide, Bacillus thuringiensis subsp. tenebrionis, were compared for their main and interactive effects on Colorado potato beetle, Leptinotarsa decemlineata (Say), populations in potato, Solanum tuberosum L. Numbers of Colorado potato beetle adults and egg masses were not significantly different in mulch versus no-mulch plots. There were fewer adults and egg masses in Asana-treated plots than in plots treated with B. thuringiensis (M-trak) or the control (untreated). Significantly fewer small (Ist and 2nd instars) and large (3rd and 4th instars) larvae were recorded in mulch treatments than in no-mulch treatments, and significantly fewer small and large larvae in Asana-treated plots compared with M-trak or untreated plots. However, the M-trak plots had significantly fewer large larvae than the untreated plots. Defoliation levels were significantly greater in no-mulch plots than mulch plots. Defoliation levels were significantly lower in Asana plots compared with M-trak or untreated plots. There was a significant interaction between mulch plus M-trak. This combination had numbers of large larvae, defoliation levels and yields as low as the Asana treatment. M-trak had its greatest effect on Ist instars and neonates, and did not affect natural enemies.