Biological control of the walnut aphid in California: Impact of the parasite, Trioxys pallidus
AuthorsR. van den Bosch
B. D. Frazer
P. S. Messenger
C. S. Davis
Authors AffiliationsR. van den Bosch (deceased) was Professor, Division of Biological Control, Department of Entomological Sciences, Berkeley; R. Hom was Staff Research Associate, Division of Biological Control, Department of Entomological Sciences, Berkeley; P. Matteson was formerly Research Assistant, Division of Biological Control, Berkeley, is with International Institute of Tropical Agriculture, Ibadan, Nigeria; B. D. Frazer was formerly Research Assistant, Division of Biological Control, Berkeley, is with Agriculture Canada, Research Station, Vancouver, B.C., Canada; P. S. Messenger (deceased) was Professor, Division of Biological Control, Department of Entomological Sciences, Berkeley; C. S. Davis was Extension Entomologist, Cooperative Extension, University of California, Berkeley.
Hilgardia 47(1):1-13. DOI:10.3733/hilg.v47n01p001. February 1979.
The interrelationship of an Iranian ecotype of Trioxys pallidas (Hal.) (Hymenoptera: Aphidiidae) and the walnut aphid, Chromaphis juglandicola (Kale), (Homoptera: Callaphididae), was assessed over a 4-year period at two localities in California. Limited additional data were obtained from other localities. Trioxys pallidas, a highly efficient parasite, which is biologically adapted to and phenologically synchronized with C. juglandicola, has brought about substantial biological control of this pest. Trioxys pallidus substantially dampens the aphid’s vernal oscillation, and normally restrains the amplitude of the summer and autumnal oscillations. Major economic benefits have been realized by the elimination of the aphid as a pest in springtime. Trioxys pallidus is at times heavily attacked by non-specific hyperparasites, but these, at most, hinder it but slightly. Certain insecticides can disrupt T. pallidus activity, permitting aphid outbreaks. Prolonged aphid scarcity, possibly abetted by hyperparasitism, also may cause a breakdown in parasite activity and a temporary aphid resurgence in midseason. During the 4 years of investigation, this occurred on one occasion in one of the study plots. More than one-half million dollars have accrued annually to the California walnut industry as a result of the C. juglandicola biological control program.
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