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United States Department of Agriculture

Agricultural Research Service

Title: Survival of Navel Orangeworm (Lepidoptera:pyralidae) During Pistachio Processing

Authors
item Johnson, Judy
item Gill, Richard
item Valero, Karen
item May, Shirley - CALIF STATE UNIV, FRESNO

Submitted to: Stored Product Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 1995
Publication Date: N/A

Interpretive Summary: All domestic pistachio production occurs in Calif., where 150 million lbs, valued at nearly $450 million, were produced in 1993. Low levels of navel orangeworm, the major field pest of Calif. pistachios, may be present in harvested nuts. Pistachio processors normally fumigate storage silos with methyl bromide shortly after drying, primarily to control postharvest infestations of Indianmeal moth, but some processors also fumigate to avoi additional damage caused by surviving navel orangeworm. Methyl bromide was recently classified as an ozone depleter, which may result in its use being restricted or eliminated. Because some proposed alternative postharvest control methods are specific to Indianmeal moth, and would not be affective against navel orangeworm, it is important to know the potential for survival of navel orangeworm in processed pistachios. A total of 1,980 kg of pistachios (about 880,000 open nuts) from two different pistachio driers swere sampled over three years. While 12,475 dead navel orangeworm of various stages were recovered from the samples, no living insects were found. The occurrence of navel orangeworm in traps placed in processing areas suggests that some navel orangeworm survive processing, but it was not possible to determine the source of the moths. Laboratory simulations of commercial pistachio drying showed that nut temperatures were above immediately lethal levels (60C) for 2.25 hours before nut moistures approached appropriate storage levels. Although limited survival of navel orangeworm eggs (2.82%) and pupae (3.33%) occurred after 30 minutes of oven exposure, no navel orangeworm survived oven exposures of 1 hour or longer. Our results show that survival of navel orangeworm in processed pistachios is very low, and should not be of major concern to processors.

Technical Abstract: The potential survival of the navel orangeworm, Amyelois transitella (Walker), in pistachios after commercial processing was estimated by sampling product from two different driers. A total of 1,980 kg of pistachios (about 880,000 open nuts) were sampled over three years. No live navel orangeworm were found and only one dead adult was discovered. Samples from drum driers, which received "floaters", had an average of 10. dead navel orangeworm per kg of product. The occurrence of moths in traps baited with virgin, laboratory-reared females suggests that some navel orangeworm survive processing, but it was not possible to determine the source of the moths. Commercial pistachio drying was simulated in a forced-air oven with an air temperature of 90C. Nut temperatures during laboratory oven drying exceeded 60C after 45 minutes, when nut moisture levels were above 26%. Nut temperatures were above 60C for 2.25 h before nut moisture content approached appropriate storage levels. Limited survival of navel orangeworm eggs (2.82%) and pupae (3.33%) occurred after 30 minutes of oven exposure, when not all nut temperatures had exceeded 60C. No navel orangeworm survived oven exposures of 1 hour or longer. Our results show that survival of navel orangeworm in processed pistachios is very low, and should not be of major concern to processors.

Last Modified: 4/21/2014
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