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Project description

Potential for Nontarget Impacts from Trichogramma platneri against Codling Moth in Walnuts in California. (98BU005)
Program UC IPM competitive research grants program
N.J. Mills, Environmental Science, Policy and Management, UC Berkeley
Host/habitat Walnuts; Tree Crops
Pest Codling Moth Cydia pomonella
Disciplines Plant Sciences, Weed Science
Trichogramma platneri
Biorational Use of Biotic Agents or Chemicals
Start year (duration)  1998 (Two Years)
Objectives Determine physiological host range and host preference of Trichogramma platneri under laboratory conditions.

Evaluate ecological host range of T. platneri under field conditions.

Determine the influence of temperature and food availability on longevity of T. platneri within the tree canopy of walnut orchards.

Investigate the effect of release rate and tree height on dispersal of T. platneri from commercial walnut orchards.

Codling moth, Cydia pomonella, is the key pest of walnuts in California and increasing resistance to synthetic insecticides has reduced the effectiveness of codling moth control. Inundative releases of an egg parasitoid, Trichogramma platneri have proved to be effective on an experimental scale, but large releases of these parasitoids may cause parasitism of non-target insect eggs. Non-target impacts of T. platneri will depend on host range and longevity.

Host range testing in the laboratory demonstrated successful oviposition and emergence of T. platneri from green lacewing, Chrysoperla carnea, corn earworm, Helicoverpa zea, and tobacco hornworm, Manduca sexta. Oviposition attempts were made on six other hosts tested (Actias luna, Automeris io, Bombyx mori, Geocoris punctipes, Nezara viridula, Spodoptera spp.) although no offspring emerged. Failure to complete oviposition in most cases was due to eggshell thickness.

In July and August of 1999 eggs of six lab-accepted hosts (C. carnea, Cydia pomonella, Ephestia kuehniella, H. zea, M. sexta, Sitotroga cerealella) were exposed to parasitism by T. platneri in a walnut orchard to examine variation in susceptibility under field conditions. Parasitism at different heights (5, 10, 15, 20, 25 feet) in the canopy was also monitored. All six hosts were equally susceptible to attack, and parasitoids were equally active at all heights in the canopy. This suggests there is no refuge for non-target insects from parasitism by T. platneri.

From May to August 1999 T. platneri were exposed to field conditions in a walnut orchard to investigate the effects of temperature and food sources on longevity. Parasitoids were held in sleeves made of dialysis tubing. The presence of food or a walnut leaf inside the sleeve increased parasitoid longevity significantly compared to sleeves without food. Median longevity was inversely related to field temperature with or without a food source inside the sleeve.

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