Biological Control of Thrips and Mite Pests of Avocado
J.
A. McMurtry
Department of Entomology,
The following report includes information presented
April 5, 1989, to the Avocado Research Advisory Committee and information
presented October 2, 1989, at the annual meeting of the California Avocado
Society.
Research continues on the imported wasp, Thripobius semiluteus, as
a biological control agent of the greenhouse thrips, Heliothrips haemorrhoidalis.
Since this parasite was introduced from
Surveys at some release sites have shown a high
percentage parasitization of thrips
by T. semiluteus (up to 70% of the second
stage thrips larva plus pupa population) and an
apparent suppression of the thrips population to low
levels. A critical factor in the success of this parasite will be its ability
to recover from severe reductions of thrips
populations resulting from early picking, parasitization,
or severe weather conditions. Although two annual cycles of both thrips and parasite populations were observed at one of our
initial parasite colonization blocks, more information is needed on this
subject.
An experiment was conducted to determine if T. semiluteus caused sufficient thrips
mortality to reduce fruit damage. Thrips numbers,
percent parasitization, and fruit scarring were
monitored in three areas of an orchard when parasites were established and
three areas where they were absent or scarce. There was a trend of lower thrips numbers and fruit damage ratings in the areas where
parasites were established, but early picking necessitated termination of the
experiment.
Although greenhouse thrips
were common in all of the six southern states surveyed in Brazil during a
two-month period beginning in March 1988, parasitized thrips
were found at only one location, an agricultural college in Lavras,
in the state of Minas Gerais. Over 200 parasites were
hand-carried to the
1988-89 Program
Greenhouse Thrips
Scheduled research: Survey release plots to determine
establishment and spread of the introduced parasitic wasp, Thripobius
semiluteus.
Thrips parasitized by T. semiluteus
have been recovered in most release plots except those which subsequently
have had very low numbers of thrips, precluding
adequate sampling. Parasitization was evident two
(and in one case three) seasons after the parasite releases. These surveys
indicate that this natural enemy is established in southern
Scheduled research: Continue insectary
production and field release of both Australian (introduced in 1986) and
Brazilian (1988 introduction) strains of T. semiluteus
for release in additional areas.
Totals of about 106,000 wasps of the Australian and
78,000 of the Brazilian strains were colonized in four counties during the
period of
Scheduled research: Determine percentage parasitization (mortality) on thrips
population by T. semiluteus, and evaluate the
effectiveness of the parasite.
Thrips and parasite populations were closely monitored in
two orchards in which the parasite has been established for at least two years.
Samples during the summer indicate an increasing mortality of second stage thrips larvae to a peak of 60-70%, and a gradual decline of
thrips populations on most sample trees. Although few
comparisons (control) trees were available on which few or no thrips were parasitized by T. semiluteus,
such trees showed delayed or no declines in thrips
numbers.
Avocado Mites
Scheduled research: Survey selected orchards to
determine establishment and spread of previously introduced beneficial phytoseiid mites.
Establishment of the predaceous mite Typhlodromus rickeri has
been observed in
Practical Applications and Summary
The introduced parasitic wasp, Thripobius
semiluteus, has become established in southern