Graduate Thesis Or Dissertation
 

The biology of the predator complex of the filbert aphid, Myzocallis coryli (Goetze), in western Oregon

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  • Commercial filbert orchards throughout the Willamette Valley were surveyed for natural enemies of the filbert aphid, Myzocallis coryli (Goetze). A large number of predaceous insects were found to prey upon M. coryli, particularly members of the families Coccinellidae, Miridae, Chrysopidae, Hemerobiidae, and Syrphidae. Also, a parasitic Hymenopteran (Mesidiopsis sp.) and a fungal pathogen (Triplosporium fresenii) were found to attack this aphid species. Populations of major predators were monitored closely during 1981 to determine phenology and synchrony with aphid populations and to determine their relative importance. Adalia bipunctata, Deraeocoris brevis, Chrysopa sp. and Hemerobius sp. were found to be extremely well synchronized with aphid population development cycles. Laboratory feeding trials demonstrated that all 4 predaceous insects tested (Deraeocoris brevis, Heterotoma meriopterum, Compsidolon salicellum and Adalia bipunctata) had a severe impact upon filbert aphid population growth. A. bipunctata was more voracious than the other 3 species, but could not live as long in the absence of aphid prey. Several insecticides were tested both in the laboratory and field to determine their relative toxicity to filbert aphids and the major natural enemies. Field tests showed Metasystox-R to be the most effective against filbert aphids, while Diazinon, Systox, Zolone, and Thiodan were moderately effective. Sevin was relatively ineffective. All insecticides tested in the field severely disrupted the predator complex. Laboratory tests showed all insecticides to be very toxic to Adalia bipunctata and Deraeocoris brevis, although Zolone caused a significantly lower mortality. Samples from a block of trees sprayed twice with Sevin showed higher aphid numbers late in the season than a comparable unsprayed block. This is interpreted as an indication that many aphid problems in commercial orchards are induced by insecticide disruption of natural biological control. Possible solutions to this problem are discussed.
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