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Project description

Field Test of More Effective Traps for the Walnut Husk Fly. (97FE042)
Program UC IPM competitive research grants program
C. Pickel, UC IPM, Sutter/Yuba counties
S. Opp, Biological Sciences, CSU Hayward
C.R. Lauzon, Biological Sciences, CSU Hayward
Host/habitat Walnuts; Tree Crops
Pest Walnut Husk Fly
Discipline Entomology
Applied Field Ecology
Start year (duration)  1997 (One Year)
Objectives Field test two new lure substances (3-methyl 1-butanol and putrescine) alone and in combination with ammonia for attractiveness to gravid female walnut husk flies in a walnut orchard.

Determine optimal dosages of the lure components in the field for monitoring walnut husk fly activity.

Field test optimal lure combinations and dosages in two commercial walnut orchards for attractiveness to gravid female walnut husk flies at the critical time when control measures are needed.

We field tested two new lure substances, 3-methyl, 1-butanol, and putrescine, alone and in combination with ammonia. Putrescine was not tested alone as Opp et al. (Unpubl.) determined its unattractive nature to walnut husk flies. While some variation occurred among blocks (typical patch dynamics associated with walnut husk flies), walnut husk flies generally were more attracted to ammonia in combination with the low dose of the butanol than any other lure either alone or in combination with ammonia during the first three weeks of testing. By the fourth week of testing, however, walnut husk flies were more attracted to ammonia and this strong attraction continued to the end of the 10 week study. Also, during the first four weeks of testing, both high and low dosage butanol lures alone captured more flies than control traps. Later in the testing season, however, control traps caught more flies than traps containing either dose of butanol with or without putrescine. Gravid female flies were first captured during the second week of the study. The attraction of flies to the butanol/ammonia lure shows promise toward specifically detecting gravid females under low population conditions and immature flies who are not attracted to ammonia. It appeared that high dosage butanol with or without putrescine in combination with ammonia diminished the attractive power of ammonia. This suggests that a repellent effect may have taken place when ammonia was mixed with high butanol alone or with putrescine. More tests need to be conducted to understand why low butanol and ammonia together are most attractive to flies early in the season, why this attraction does not continue, and if we alter dosage can we extend the attractive nature of this combination. In addition, the possible repellent effect of butanol should be examined for possible use in new trapping strategies.

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