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United States Department of Agriculture

Agricultural Research Service

Title: Determination of the development rate of navel orangeworm (Amyelois transitella)in pistachios and assessment of population structure and winter mortality

Authors
item Siegel, Joel
item Kuenen, Lodewyk
item Higbee, Bradley - PARAMOUNT FARMING
item Bettiga, James - S&J RANCH

Submitted to: California Pistachio Commission Production Research Report
Publication Type: Trade Journal
Publication Acceptance Date: January 15, 2007
Publication Date: March 1, 2007
Citation: Siegel, J.P., Kuenen, L.P., Higbee, B.S., Bettiga, J. 2007. Determination of the development rate of navel orangeworm (Amyelois transitella)in pistachios and assessment of population structure and winter mortality. California Pistachio Commission Production Research Report. p.37-44.

Interpretive Summary: A series of laboratory and field studies were conducted to determine the rate of development of navel orangeworm in pistachios. These are the first reported data on development rate on this host. Development was evaluated on early splits, split nuts collected in Mid August, split nuts collected in September, low grade processed pistachios and unharvested pistachios collected in May. Development was dependent on nut quality and was fastest on split nuts collected in late July and mid August and longest on unharvested nuts collected in May (mummy nuts). The shortest mean development time was 725 degree days (DD) Fahrenheit and the longest mean development time was 1,776 DD°F on mummy nuts. Focusing on the mean rates may be misleading because adults can develop in less than 400 DD °F, and the other tail of the population can take as long as 2,800 DD °F. Insecticide application strategies may need to be altered because of these different rates. These data can be combined with our data on adult emergence from mummy nuts to develop a model for adult flight activity. We also assessed adult mortality throughout the winter and the greatest decrease that can be attributed solely to mortality occurred between December and February, 89%. Although the population continued to decline after early February, this decline was due to a combination of mortality and adult emergence. Unharvested nuts serve as a resource for the overwintering population and the density of useable nuts also declined throughout the winter, although the decline was greater in 2005 than 2006. In both years, there were still thousands of nuts per acre available for the spring population of navel orangeworm to use.

Technical Abstract: A series of laboratory and field studies were conducted to determine the rate of development of navel orangeworm in pistachios. These are the first reported data on development rate on this host. Previous researchers utilized a development rate of 1024-1056 degree days developed from nonpareil almonds. Navel orangeworm development in this study was evaluated on early splits, split nuts collected in Mid August, split nuts collected in September, low grade processed pistachios and unharvested pistachios (mummies) collected in May. Development was dependent on nut quality and was fastest on split nuts collected in late July and mid August and longest on unharvested nuts collected in May (mummy nuts). The shortest mean development time was 725 degree days (DD) Fahrenheit and the longest mean development time was 1,776 DD°F on mummy nuts. The mean development rate in early splits ranged from 725 – 839 degree days, the mean development rate in mature split nuts ranges from 1,012-1,024 DD°F, the mean development rate in low grade processed nuts ranged from 1,073 - 1,304 DD°F, and the mean rate in May mummies was 1,776°F. Focusing on the mean rates may be misleading because adults can develop in less than 400 DD °F, and the other tail of the population can take as long as 2,800 DD °F. Insecticide application strategies may need to be altered because of these different rates. These data can be combined with our data on adult emergence from mummy nuts to develop a model for adult flight activity. According to our model, there are four flights comprising three generations in Madera County; there is at least an additional flight in Kern County. We also assessed adult mortality throughout the winter and the greatest decrease that can be attributed solely to mortality occurred between December and February, 89%. Although the population continued to decline after early February, with a reduction in infestation of 93% between February and April, this decline was due to a combination of mortality and adult emergence. Unharvested nuts serve as a resource for the overwintering population and the density of useable nuts also declined throughout the winter, although the decline was greater in 2005 than 2006. In both years, there were still thousands of nuts per acre available for the spring population of navel orangeworm to use. In early to mid June 2005, 0.04% of the mummies recovered on the ground were still infested. These data indicated that sanitation in pistachios can be a problem and that further research is needed to augment sanitation.

Last Modified: 9/21/2014
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