Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids ofthe genus Dysaphis in apple orchards
P. Kehrli et E. Wyss, Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids ofthe genus Dysaphis in apple orchards, ENT EXP APP, 99(2), 2001, pp. 245-252
The impact of augmentative releases of indigenous predators and insecticide
applications to control the autumn aphid forms of the genus Dysaphis (Homo
ptera: Aphididae), major pest insects on apple trees, was assessed in one-y
ear field experiments in Switzerland. Eggs and larvae of the two-spot ladyb
ird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) were released
on 4-year old apple trees in various numbers at five different dates in au
tumn 1998 when sexuales of the aphids were present. Additionally, Pyrethrum
HP was sprayed at the same five dates to compare the effectiveness of thes
e augmentative releases to a commonly applied insecticide. Augmentative rel
eases of larvae before mid-October significantly prevented the deposition o
f overwintering eggs by aphids of the genus Dysaphis and consequently reduc
ed the number of hatched fundatrices in spring, 1999. There was a significa
nt negative functional response among the number of released coccinellid la
rvae in autumn 1998 and the number of observed fundatrices on apple trees i
n spring 1999. Applications of Pyrethrum HP before mid-October were more ef
fective than augmentative releases of larvae of A. bipunctata. The release
of coccinellid eggs had no impact on the number of fundatrices of the genus
Dysaphis in the next spring because they did not hatch due to bad weather
conditions. The weather conditions in autumn seemed to have an impact on th
e autumn migration of the winged aphids back to their primary host. The pre
vention of egg deposition of aphids in autumn is a promising control strate
gy and deserves further exploration for practical use.