AN INTEGRATED INSECT
CONTROL PROGRAM
FOR STREET TREES

W. OLKOWSKI + C. PINNOCK - W. TONEY + G. MOSHER

W. NEASBITT -

Over the last three years the Recreation and
Parks Department of the City of Berkeley
has worked with members of the Department
of Entomological Sciences, University of Cali-
fornia, Berkeley, to develop an integrated
insect control program for the city’s 30,000
street trees. The program has virtually elimi-
nated synthetic chemical insecticides as
regular management tools on the city’s 123
species of shade trees. This program has
resulted in lower. pest management cests,

OST STREET TREES are not native

to the region in which they are
planted and are therefore subject to oc-
casional invasions by insects that he-
long to exotic ecosystems, Often a plane.
feeding insect invades an area that lacks
the beneficial insects which would serve as
natural controls on the invading species.
The frequent result is an abnormally high
population which natural enemies in the
invaded system cannot control. Such in-
sect problems may he permanently solved
by classical biological control, which in-
volves determining the native area of the
pest, a searching in that area for its
natural enemies (parasites and preda-
tors}, identifying the carnivores, select.
ing candidates for importation, collecting
and shipping them, subjecting them to
quarantine processing (where all but the
desired new species are destroyed) and
finally, colonizing the imported natural
enemies on specific host insects. This pro-
cedure was successfully followed for three
species of aphids (£ucallipterus tiliae,
Tinocallis platani, Tuberculoides annu-
latus), which attacked linden, elm and
English oak trees, respectively, They
were hrought under control by the follow.
ing five species of parasitic wasps: (1)
Trioxys curvicaudus Aphidiidae and (2)
Mesidiopsis subflavescens Aphelinidae,
both from France and ltaly: (3) Mesidi.

R. VAN DEN BOSCH -

fewer citizen complaints, elimination of
secondary pest outbreaks and a reduction
in environmental contamination. By reducing
the amount of pesticides used, the city of
Berkeley saves about $22,500 each year in
labor and pesticide costs. The current pro-
gram is a synthesis of various non-toxic man-
agement methods including biological,
microbial, cultural, physical—along with the
judicious use of chemical controls, when
needed.

opsis subflavescens Aphelinidae, from
Czechoslovakia; (:4) Trioxys palitdus
Aphididae, from Holland: and ¢5) A.
subflarescens Aphelinidae from Italy.
These wasps reduced the aphid popula.
tion to the point where insecticides have
become unnecessary. Since these host.
specific parasitie wasps have overwin-
tered and propagated themselves, no other
control efforts are anticipated,

Many species of caterpillar, including
California oakworm (Phryganidia cali.
fornica}, may he safely and selectively
contralled hy Bacillus thuringtensis
sprays, This spray is available in several
commercial formulations, some of which
were used for oakworm control in 1969
by the California Division of Highways
and by the City of Berkeley in 1970, Bo
cause B. thuringiensis kills only caterpil-
lars, no harm is caused to the beneficial
insects, birds and animals that provide
biological control of other potential pests,

Water sprays

High pressure water spraying was sub.
stituted for insecticides on elm. English
oak, birch, pyracantha, plum. searlet
oak, beech, ash and big leaf maple. With
trees greater than 30 ft in height. line
pressures were increased to 600 psi to
permit coverage of the highest parts of
the infested portions of trees, Some large

H, OLKOWSKI

trees were only partially sprayed to re-
move localized infestations. Disadvan.
tages of this technique inelude the possi-
bility of severe leaf removal by the spray
on lower portions of trees, fraving of
foliage and excessive mortality to bene-
ficial insects. However, through proper
seasonal timing and adjustment of line
Pressures, water spraying is an extresaely
useful, inexpensive and harmless pest con-
trol technique.

Adhesive bands

The Argentine ant (lridomyrmex hu-
milis) occurs on most street trees in
Berkeley and is associated with all of
the pest aphid species, In many cases
I. Aumitis increases population levels of
honevdew producers, especially aphids.
hy interfering with heneficial insect popu.
lations, When aphid and ant populations
are excessive, sticky adhesive bands of
“Stickem” (1 inch wide, and VS inch
thick ahout 5 ft above ground) around
tree trunks exclude ants and reduce aphid
populations, This barrier is effective dur.
ing «pring, summer and fall. and al.
though unsightly to some people. captures
many insects. particularly flies. It also
stops the passage of predators that have
fallen from trees, but provides a non.
toxic aphid control and ant management
tool useful in urban areas,

Since many of Berkeley's pest aphids
prefer the inner portions of host trees
where the vegetation is usually more suc.
culent and the temperatures are cooler,
their populations can be reduced hy selec.
tive pruning. Pruning for the reduction of
preferred aphid food sources was used
successfully on linden. elm, English oak
and ush,

In 1972 reduced amounts of the in-
secticides diazinon and dimethoate were
used hecause of better monitoring with
fewer unnecessary treatments. In 1973
it was necessary to spot treat (with diaz.
inon} six sweet gums ‘Liguidambar