ARS | Publication request: Evaluation of a Granulovirus (PoGV) and Bacillus Thuringiensis subsp. kurstaki for Control of the Potato Tuberworm in Stored Tubers

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 2008
Publication Date: October 9, 2008
Citation: Arthurs, S.P., Lacey, L.A., De La Rosa, F.L. 2008. Evaluation of a Granulovirus (PoGV) and Bacillus Thuringiensis subsp. kurstaki for Control of the Potato Tuberworm in Stored Tubers. Journal of Economic Entomology 101:1540-1546.

Interpretive Summary: The potato tuber moth (PTM) is an invasive species of the Pacific Northwest of the United States that has recently caused damage to potato field crops and also tubers in storage facilities. Currently, there are no insecticides for PTM control in stored potato tubers. One possible solution to PTM damage to stored tubers is the use of low risk biological pesticides that could have few or no restrictions on their use. In 2006 and 2007, scientists at the Yakima Agricultural Research Laboratory in Wapato, Washington have evaluated an insect-specific virus (PoGV) and a bacterium Bacillus thuringiensis var. kurstaki (Btk), for control of PTM on stored tubers. Results of experiments showed that both PoGV and Btk may be used as biological insecticides, although PoGV was the more effective of the two and killed up to 100% of larvae on tubers that were treated before being infested with PTM larvae. Potatoes that were infested and then treated also demonstrated a high level of mortality in PTM. Both PoGV and Btk provided excellent non-chemical control of PTM on stored tubers.

Technical Abstract: Currently no insecticides are registered for postharvest use on potato tubers in North America. We evaluated liquid suspensions and dry formulations of a granulovirus (PoGV) and bacterium Bacillus thuringiensis subsp. kurstaki Berliner (Btk) for control of the potato tuber moth (PTM), Phthorimaea operculella Zeller, in stored tubers. Laboratory bioassays at 25 degrees C showed that both PoGV (derived from infected larvae) and a WP formulation of Btk incorporated with carriers [talc, sand, diatomaceous earth (DE) and kaolin clay], were effective against neonate larvae. Tubers could alternatively be dipped in test suspensions and dried prior to infestation. Depending on the technique employed, 100% larval mortality was achieved at concentrations as low as 0.025 larval equivalents (LE)/kg tuber (PoGV) and 150 mg kg tuber (Btk). Howver, 100% mortality was never achieved with tests on pre-infested tubers, ostensibly due to the higher dosage required to kill older instars inside tubers. The most effective PoGV formulations overall were dipping and talc, with dipping most effective for post-infestation treatments causing up to 91.6% mortality at 0.4 LE/kg. There was no significant effect of formulation in the Btk treatments. The protective effects of residues were also evaluated under longer-term storage conditions. Batches of tubers treated with PoGV or Btk via dipping (up to 0.1 LE and 150 mg kg/tuber) were stored in cages containing an initial PTM infestation (10% of tubers). Although PTM populations were reduced by up to 98.4% after 2 months at 25 degrees C, no treatments prevented reproduction of the F1 generation of PTM (which had been expected) or prevented significant additional tuber damage from occurring. No significant treatment effects were detected in similar cages held at 12 degrees C for 4.5 months. The slow development of PTM at this lower temperature did not allow us to fully quantify the effect of treatments. Improved strategies to use PoGV and Btk for long term control of PTM in tuber stores are discussed.