Evaluation of a Granulovirus (PoGV) and Bacillus thuringiensis subsp. kurstaki for Control of the Potato Tuberworm (Lepidoptera: Gelechiidae) in Stored Tubers

Abstract

Liquid suspensions and dry formulations of a granulovirus (family Baculoviridae, genus Granulovirus, PoGV) derived from infected larvae and the bacterium Bacillus thuringiensis subsp. kurstaki (Berliner) (Btk) were evaluated for control of the potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), in stored tubers. Laboratory bioassays at 25 degrees C showed that both PoGV and a wettable powder (WP) formulation of Btk incorporated with carriers (water, talc, sand, diatomaceous earth, and kaolin clay), were effective against neonate larvae. Depending on the technique, 100% larval mortality was achieved at concentrations as low as 0.025 larval equivalents (LE) PoGV per kg tuber and 150 mg Btk WP per kg tuber. However, 100% mortality was never achieved with tests on preinfested tubers, ostensibly due to the higher dosage required to kill older instars inside tubers. The most effective PoGV formulations were dipping (water) and talc, with dipping most effective for postinfestation treatments, causing up to 91.6% mortality at 0.4 LE per 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 WP per kg tuber) were stored in cages containing an initial potato tuberworm infestation (10% of tubers). Although potato tuberworm populations were reduced by up to 98.4% after 2 mo at 25 degrees C, no treatments prevented the development and reproduction of the F1 generation. The sprouting of stored tubers seemed to be a limiting factor for sustained control. No significant treatment effects were detected in similar cages held at 12 degrees C for 4.5 mo. Improved strategies for the application of PoGV and Btk for long-term potato tuberworm control in tuber stores, including the use of chemical sprout suppressants, are discussed.

Insecticidal Activity of the Granulosis Virus in Combination with Neem Products and Talc Powder Against the Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

“…At the highest rate (5×10 8 ) of both aqueous suspension and virus formulation, no feeding damage of first instars on the tubers was observed (data not shown), and most likely due to overdose. Arthurs et al (2008) also verified 100% potato tuberworm larval mortality with concentrations as low as 5.75×10 8 OBs/kg. Talc was tested as a dust carrier for virus OBs, but we observed that the talc itself strongly affected larval mortality of potato tuberworm due to its fast desiccation effect against newly hatched larvae, as previously described elsewhere (Alcázar et al 1992b, Arthurs et al 2008.…”

“…Arthurs et al (2008) also verified 100% potato tuberworm larval mortality with concentrations as low as 5.75×10 8 OBs/kg. Talc was tested as a dust carrier for virus OBs, but we observed that the talc itself strongly affected larval mortality of potato tuberworm due to its fast desiccation effect against newly hatched larvae, as previously described elsewhere (Alcázar et al 1992b, Arthurs et al 2008. Some dry powder carriers have been used as an alternative to synthetic insecticides and are thought to act by imposing mechanical disruption (e.g., mouth parts injuries on chewing insects such as beetles and caterpillars) and physiological stress by absorbing wax from the insect cuticle resulting in water loss (Ebeling 1971, Korunic 1998).…”

“…Our results demonstrated that talc mixed with low or medium concentrations of the granulosis virus for dusting tubers provides better effectiveness than aqueous virus suspension treatment against potato tuberworm. The use of granulosis virus with talc is simple and nontoxic to humans, and can be an economically viable option recommended to farmers to protect seed tubers for at least 2 months in rustic potato storage systems (Alcázar et al 1992b, Arthurs et al 2008.…”

“…A dry powder formulation of granulosis virus containing occlusion bodies (OBs) incorporated into talc has been successfully developed and marketed by the International Potato Center in Lima, Peru, as a nontoxic method to protect tubers in nonrefrigerated storage facilities (Lagnaoui et al 1997). Talc-based formulations have also been tested for potato tuberworm control in nonrefrigerated storages (Alcázar et al 1992b, Arthurs et al 2008 and in field trials (Salah & Aalbu 1992) with some success. However, the median lethal concentration of virus talc-based formulation in comparison with aqueous virus suspensions remains undetermined.…”

The Potato Tuberworm: A Literature Review of Its Biology, Ecology, and Control

“…However, microbial control of P. operculella is not yet developed for massive commercial use although some authors have indicated the potential use of those pathogens in the future (Lacey and Arthurs 2005;Arthurs et al 2008). In fact, some small scale tuberworm control by microbes has been already used successfully (Kroschel et al 1996a, b;Sporleder et al 2001Sporleder et al , 2005Sporleder 2003).…”