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
