Imported parasitic wasp helps control red gum lerp psyllid

Abstract

The red gum lerp psyllid is an insect native to Australia, where it feeds upon eucalyptus
species. Since 1998 this psyllid has spread throughout California, resulting in millions
of dollars in damage and control costs. To help suppress the red gum lerp psyllid,
a biological control program was initiated and a psyllid-specific parasitic wasp was
imported from Australia in 1999 and released in 2000. In most coastal regions this
biological control agent has provided substantial control, but in some interior regions
the psyllid still remains a problem. Researchers are continuing their investigations
to determine if full statewide suppression will be realized eventually, or if further
importation of new parasitoid species is needed.

Full text

http://CaliforniaAgriculture.ucop.edu • OCTOBER–DECEMBER 2005 229
Donald L. Dahlsten
Kent M. Daane
Timothy D. Paine
Karen R. Sime
Andrew B. Lawson
David L. Rowney
William J. Roltsch
John W. Andrews Jr.
John N. Kabashima
David A. Shaw
Karen L. Robb
James A. Downer*
Pamela M. Geisel
William E. Chaney
Chuck A. Ingels
Lucia G. Varela
Mary L. Bianchi
Gary Taylor
▼
The red gum lerp psyllid is an insect
native to Australia, where it feeds
upon eucalyptus species. Since 1998
this psyllid has spread throughout Cal-
ifornia, resulting in millions of dollars
in damage and control costs. To help
suppress the red gum lerp psyllid, a bi-
ological control program was initiated
and a psyllid-specific parasitic wasp
was imported from Australia in 1999
and released in 2000. In most coastal
regions this biological control agent
has provided substantial control, but
in some interior regions the psyllid
still remains a problem. Researchers
are continuing their investigations to
determine if full statewide suppres-
sion will be realized eventually, or if
further importation of new parasitoid
species is needed.
Eucalyptus trees and shrubs, valued
for their ability to flourish in arid
regions and their varied horticultural
uses, have been a familiar feature of
California’s urban and rural landscapes
since they were first introduced from
their native Australia more than 150
RESEARCH ARTICLE
▼
Imported parasitic wasp helps
control red gum lerp psyllid
years ago. Until recently, eucalyptus
trees in California were relatively free
from damaging insect pests. Most of
California’s native insects cannot feed
on eucalyptus, which is well protected
from herbivores by chemicals such as
distasteful essential oils (which are fa-
miliar to anyone who has smelled the
strong odor of the leaves). The Austra-
lian insects that have adapted to feed
on eucalyptus were not transported to
California with earlier shipments of
plant propagation material, usually
in the form of seeds. This began to
change in the early 1980s and at least
15 eucalyptus-feeding insect species
from Australia were accidentally intro-
duced and are now established in Cali-
fornia (Paine and Millar 2002). While
eucalyptus trees may be unwanted in
some areas because they crowd out na-
tive vegetation, their extensive value in
many other locations led to efforts to
control the psyllid.
River red gum (Eucalyptus camal-
dulensis) is among the most com-
monly planted shade and windbreak
trees in California and is also grown
commercially for fuel wood and fi-
ber (Cockerham 2004). The red gum
lerp psyllid (Glycaspsis brimblecombei
Moore; Hemiptera: Psylloidea) was
first found on river red gum in June
1998 in Los Angeles County and had
spread throughout the state by 2000,
and throughout Mexico and parts of
Florida by 2002. In Australia there are a
number of eucalyptus species that the
red gum lerp psyllid can feed on, but in
California the only favored eucalyptus
species present is the river red gum;
the forest red gum (E. tereticornis) and
flooded gum (E. rudis), both also in
California, are less-favored trees that the
psyllid can feed on as well.
Red gum lerp psyllid nymphs build
white conical shelters called lerps from
excreted honeydew and waxes, and
live underneath these structures. The
nymphs feed by sucking plant sap from
leaves. The accumulation of the sticky
lerps and honeydew on leaves and
under infested trees creates a nuisance,
while heavy infestations lead to defolia-
tion, branch dieback and occasionally
tree death (Paine et al. 2000).
The first attempts to control red
gum lerp psyllid focused on the use of
The parasitoid Psyllaphaegus bliteus has
been released throughout California to
control the red gum lerp psyllid, a pest of
eucalyptus. Above, an adult P. bliteus uses
its ovipositor to place an egg inside the
red gum lerp psyllid nymph. The parasitoid
develops inside the psyllid nymph, which
typically does not show any signs of parasit-
ism until the nymph reaches the fifth instar,
when the parasitoid pupa — far left, white
body, and left, dark body — can be seen
through the mummified psyllid.
*Author’s correction after press time.

230 CALIFORNIA AGRICULTURE • VOLUME 59, NUMBER 4
▼
Clockwise from top left: Karen Sime, UC Berkeley
postdoctorate researcher, checks a caged eucalyptus leaf
for evidence of P. bliteus activity and parasitism rates;
the late Don Dahlsten (first author) was a leading UC
researcher (1966–2003) in biological control of urban and
forest pests (shown in 1974); small discs coated with a
light oil were used to capture and sample populations
of adult red gum lerp psyllid and P. bliteus; red gum lerp
psyllids feed on eucalyptus leaves, building up to such
high densities that the accumulation of psyllids and
honeydew causes sooty molds, defoliation and even
tree death; in the San Joaquin Valley (Tulare County), a
dead red gum eucalyptus (left) near an undamaged and
uninfested blue gum eucalyptus (right) demonstrates the
psyllid’s feeding preferences.
systemic insecticides, mainly to target
heavy infestations on particularly valu-
able trees. The proper timing of treat-
ments was difficult to determine and
control was not always achieved (Paine
et al. 2000). The obvious impracticality
of using insecticide treatments on trees
throughout the state led us to investi-
gate more sustainable options. We first
investigated whether any predators
already present in California could pro-
vide control. Lady beetles (Hippodamia),
green lacewings (Chrysoperla), minute
pirate bugs (Orius) and syrphid flies
feed on adult and immature red gum
lerp psyllids (Erbilgin et al. 2004).
However, even when present in large
numbers, these predators did not pro-
vide adequate control.
In Australia, red gum lerp psyllid
populations are held in check in large
part by species of parasitic wasps that
specifically attack them and their close
relatives. Other parasitoid species im-
ported from Australia had successfully
controlled earlier outbreaks of other
introduced Australian psyllid species
in California, including the blue gum
psyllid (Dahlsten et al. 1998) and the
eugenia psyllid (Dahlsten et al. 1995).
Classical biological control appeared,
therefore, to be the most promising
approach for controlling the red gum
lerp psyllid. We report here on a large
collaborative effort between UC, the
California Department of Food and
Agriculture (CDFA) and research scien-
tists in Australia.
Prerelease psyllid sampling
Before the biological control program
began, we gathered detailed information
about red gum lerp psyllid populations
throughout California. Beginning in July
1999, sample sites were established in
Alameda, Santa Clara, Monterey, Los
Angeles and San Diego counties. By July
2002, we had established 32 sample sites,
with at least one site located in every
California county in which red gum lerp
psyllid had been reported.
Sampling psyllid populations ac-
curately can be difficult. The most
accurate way of measuring densities
and damage levels is to count psyllid
nymphs on leaves. This method, how-
ever, is time-consuming and impracti-
cal for the large number of sample sites
and frequent sampling dates needed to
follow psyllid and natural-enemy pop-
ulation dynamics throughout the state.
We therefore investigated whether red
gum lerp psyllid populations could
be tracked with sticky traps, which
had been used for the blue gum and
eugenia psyllid programs (Dahlsten et
al. 1998). The traps consisted of trans-
parent 4-inch (10-centimeter) plastic
disks coated with a thin layer of motor
oil additive and clipped over a yellow
backing. At each site, 10 to 12 traps
were hung in eucalyptus trees and
changed weekly.
In 1999 and 2000, we tested trap ac-
curacy at two sites, one in Northern
California (Alameda County) and
the other in Southern California (Los
Angeles County). Near each trap at
these sites, two 12-inch (30-centimeter)
foliage samples were collected every
3 weeks (20 to 24 samples per site per
sample date). We found a good cor-
relation between the mean number of
adult female psyllids per sticky trap
and the mean number of psyllid eggs
per leaf sample (P < 0.01, r2 = 0.82;
Paine et al. [2000]), indicating that the
sticky-trap counts provided a good es-
timate of psyllid activity in eucalyptus.
Thereafter, we relied exclusively on the
▼ Below, life stages of the red gum lerp psyllid include,
(left to right) large nymph, row of eggs, winged adult and
small lerp (the protective covering produced by nymphs).
Jack Kelly Clark
Jack Kelly Clark

http://CaliforniaAgriculture.ucop.edu • OCTOBER–DECEMBER 2005 231
sticky-trap technique to monitor the
psyllids. In addition, we used the same
traps to monitor parasitoid populations
after we began releasing them.
Initially, we counted both male and
female adult psyllids per trap by sample
week. However, we noticed strong
seasonal changes in the relative propor-
tions of adult females and males. For
example, female psyllids typically had
the highest populations in the summer
months and dropped significantly the
rest of the year. Because their numbers
are most closely associated with egg-
laying (and thus nymphal activity and
damage), we plotted only the adult
female psyllids caught on the traps. At
each monitoring site, we reported the
averages of 10 to 12 traps.
Finding, importing parasitoids
To find promising parasitoids,
mummified red gum lerp psyllids
were field-collected and shipped from
southern Australia to the UC Berkeley
Quarantine Facility in August 1999 (the
“mummified” psyllid is visibly dead,
killed by the internal parasitoid that
is nearing completion of its develop-
ment). This region, near Adelaide, has
a Mediterranean climate, with tempera-
tures similar to California’s coastal re-
gions. From the field-collected psyllids,
we reared eight species of parasitoids in
the genus Psyllaephagus (Hymenoptera:
Encyrtidae). Of these, two were hy-
perparasitoids (which attacked the
beneficial “primary” parasitoids) that
attacked the other Psyllaephagus species,
and most others failed to propagate in
the insectary. The remaining species
(Psyllaephagus bliteus Riek) did well in
culture and was selected for release
after experiments showed that it specifi-
cally attacked the red gum lerp psyllid
when tested against three other psyllid
species (Eugenia, blue gum and mela-
leuca) (Paine et al. 2000).
Parasitoid biology. To facilitate in-
sectary rearing and field release, we
collected basic biological information
on P. bliteus (Daane et al. 2005). First,
we determined which stages of the host
(red gum lerp psyllid) were preferred
by the female parasitoids (P. bliteus) for
oviposition. Potted eucalyptus trees were
infested with 300 to 500 psyllid nymphs,
with the population composed of all five
nymphal stages in similar proportions,
and isolated in organdy sleeve cages
with 15 to 20 adult female P. bliteus. After
24 hours, all psyllids were collected and
cleared in chloralphenol, which makes
any P. bliteus eggs inside the psyllid
body visible under a dissecting micro-
scope. The number of eggs and the psyl-
lid stages were recorded. We also used
similar methods to investigate P. bliteus
larval development.
We collected the psyllids every 3 to
4 days after exposure to female wasps,
cleared them in chloralphenol, and
then recorded both the presence of P.
bliteus eggs or larvae and the develop-
mental stages of parasitized psyllids.
There were five host preference and
four larval development replicates; the
treatment means were separated using
Tukey’s HSD test. Our results showed
that P. bliteus can oviposit into psyllid
nymphs of any age, but that they usu-
ally parasitize third and fourth instars
(fig. 1). In our studies, regardless of the
stage of the host exposed to P. bliteus
for oviposition, the parasite larvae did
not fully develop until after the host
reached the fifth (last) instar. In addi-
tion, adult female wasps also occasion-
ally killed psyllid nymphs by host
feeding, stabbing them with their ovi-
positors and drinking the body fluids
leaking out from under the lerp. Usually
younger nymphs are attacked but we
observed this host feeding on all stages.
Longevity and fecundity. Adult
P. bliteus longevity and fecundity were
also determined. Newly emerged and
mated female P. bliteus were individu-
ally isolated in clear plastic tubes that
each enclosed a single infested leaf
on a potted river red gum tree in the
glasshouse (71.6 ± 3°F). Each leaf was
infested with 10 to 30 psyllids, mostly
third instars. Each female P. bliteus was
transferred to a new leaf every 2 days
throughout her lifetime. After each
transfer, the parasitoid-exposed psyllids
were cleared in chloralphenol, and the
presence of P. bliteus eggs was recorded.
Under these conditions, we found that
average female P. bliteus longevity was
60.4 ± 6.4 days and average lifetime
egg deposition was 125.7 ± 24.6 eggs
per female (range 34 to 302). Most eggs
(88.1%) were deposited during the ini-
tial 22 days, although one parasitoid
deposited eggs up to 70 days after emer-
gence (fig. 2).
These results have implications for
insectary operations and release strate-
gies in classical biological control pro-
grams. Although adults may survive
for long periods, most egg deposition
occurs early in the adult’s lifetime.
Insectary colonies should therefore be
supplied with the needed number of
Fig. 1. P. bliteus oviposition success in different host develop-
mental stages, as indicated by the percentage egg deposition
(± SEM) of parasitized red gum lerp psyllids, was significantly
different (F = 12.48, df = 4,25, P < 0.001). Above each bar,
means followed by different letters are significantly different
(Tukey’s HSD test, P < 0.05). Source: Daane et al. (2005).
Fig. 2. P. bliteus lifetime fecundity under glasshouse conditions, as
estimated by egg deposition with an overabundant host supply.
Source: Daane et al. (2005).

232 CALIFORNIA AGRICULTURE • VOLUME 59, NUMBER 4
June 2000 in Los Angeles and Alameda
counties. Between September 2000 and
January 2003, we released a total of
48,582 adults in 78 release sites located
in 42 counties throughout the state
(1,156 ± 154 per county, range 50 to
4,016) (table 1).
Parasitoids were recovered in sticky
traps as early as 8 weeks after initial
release. Recovery in traps occurred ear-
liest in the Central Coast sites, followed
by the Southern California, North
Coast and Central Valley sites (table
2). Psyllid densities typically peaked
between August and October, and these
peak periods were used to compare an-
nual changes at each site. Eastern Los
third- or fourth-instar psyllids for an
oviposition period of 2 to 3 weeks. In
addition, first or second instars should
also be provided because they are used
for host feeding. Finally, the parasitic
wasps can be released to the field
shortly after emergence and mating, as
high rates of egg deposition begin im-
mediately.
Parasitoid release and impact
For field release, most parasitoids
were reared at the CDFA Biological
Control Facility (Sacramento), with
smaller numbers reared at the UC
Berkeley Insectary and Quarantine
Facility. Release of P. bliteus began in
Fig. 3. Red gum lerp psyllid adult females and P. bliteus parasitoid
adults (both mean per trap per week) and parasitoid release dates
in a single site each in (A) eastern Los Angeles County, (B) San Mateo
County (parasitoids originally released in nearby counties) and
(C) southern Sacramento County.
Angeles County is an example of a site
with a marked decrease in psyllids and
an increase in parasitoids (fig. 3A). Peak
psyllid counts dropped from more than
100 in 1999 (before the wasp release)
to fewer than 20 females per trap per
week in 2003 (after the second wasp
release). During the same period, trap
catches of P. bliteus increased for 3 years
after the initial release in June 2000 and
then showed steady seasonal cycles. A
similar pattern of psyllid decrease and
parasitoid increase was found farther
north, in San Mateo County (parasitoids
were originally released in nearby coun-
ties) (fig. 3B). In contrast, P. bliteus has
to date had less effect on psyllid densi-
TABLE 1. P. bliteus releases by California county, 2000 to 2003, show
the widespread collaborative effort to release and establish the
imported red gum lerp psyllid parasitoid
County Sites Releases Release period Released
no. no. no.
Alameda 2 5 June 2000–Aug 2001 571
Amador 1 2 Aug 2002 802
Butte 1 1 July 2002 735
Calaveras 1 1 June 2002 1,047
Colusa 1 1 July 2002 408
Contra Costa 1 1 May 2002 654
Fresno 1 2 Nov 2000, Aug 2001 473
Glenn 1 1 Sep 2001 569
Imperial 2 1 June 2002 998
Kern 1 1 July 2002 245
Kings 1 1 May 2002 522
Lake 1 1 Sep 2002 625
Los Angeles 8 15 June 2000–June 2002 4,016
Madera 1 1 June 2002 752
Marin 1 1 May 2002 571
Mariposa 2 2 Aug 2002, Jan 2003 728
Merced 1 1 Nov 2001 933
Monterey 2 2 Dec 2000, Sep 2001 518
Napa 1 1 Apr 2002 650
Orange 3 4 Nov 2000, Dec 2001 1,846
Placer 2 2 July, Sep 2002 1,514
Riverside 6 7 Nov 2001–Mar 2002 3,910
Sacramento 4 8 Oct 2000–June 2002 3,070
San Benito 1 1 Aug 2002 587
San Bernardino 5 5 Oct 2001–Mar 2002 3,775
San Diego 3 8 Sep 2000–May 2002 1,914
San Joaquin 2 2 Apr, Sep 2002 1,070
San Luis Obispo 1 3 Sep 2001–Jan 2002 2,863
Santa Barbara 2 2 Feb, July 2001 217
Santa Clara 2 1 Sep 2000 50
Santa Cruz 1 1 Aug 2002 610
Shasta 3 2 June 2002 2,002
Solano 1 2 Sep 2001, July 2002 1,405
Sonoma 1 2 Sep, Oct 2001 1,309
Stanislaus 1 1 May 2002 836
Sutter 2 2 May, June 2002 1,465
Tehama 2 2 Oct 2000, June 2002 1,048
Tuolumne 2 2 Aug, Oct 2002 875
Tulare 1 1 June 2002 800
Ventura 1 1 Sep 2000 71
Yolo 1 1 June 2002 573
Yuba 1 1 June 2002 955
Totals: 78 102 48,582

http://CaliforniaAgriculture.ucop.edu • OCTOBER–DECEMBER 2005 233
TABLE 2. Average number of days
(± standard error) between initial P. bliteus
release and recovery in traps in four
California regions (see fig. 4)
Region Sites Days ± SE
Central Valley 2 623 ± 28.0
North Coast 5 302 ± 59.7
Central Coast 5 156 ± 56.6
Southern California 13 252 ± 32.9
ties in some interior sites. For example,
3 years after parasitoid releases at one
Sacramento County location, parasitoid
levels were relatively low and psyllid
numbers remained high (fig. 3C).
To summarize the changes in psyl-
lid density across all 32 monitored
sites, we compared the average peak
densities of psyllids per trap in 2003 to
those in years before the parasitoid was
established (1999 to 2001). The results
of this comparison, grouped by region,
indicate a postrelease drop in peak psyl-
lid densities of 78.6%, 59.5% and 44.8%
in the southern, central and northern
coastal regions, respectively. There was
no change in peak psyllid densities in
the Central Valley sites. The postrelease
rate of increased parasitoid activity was
estimated by calculating the average
time from the release to a 50% or more
decrease in peak psyllid density on the
monitoring traps. At most coastal sites
(18 out of 23) the average time to a 50%
decrease in psyllid density was 13.2 ±
1.2 months after the initial parasitoid re-
lease. By comparison, at the nine Central
Valley sites monitored, there was little
or no detectable effect of P. bliteus on the
psyllid population densities during the
2001 to 2003 sampling period.
Coastal versus interior sites
The differences in parasitoid ef-
fectiveness between coastal and inte-
rior sites were most likely due to the
great climatic differences between the
two regions. The coastal region has
relatively mild summer and winter
temperatures, while the interior val-
leys have much cooler winters and
warmer summers. To date, the Central
Valley sites lag behind the coastal sites
in two measures of parasitoid impact:
the time to establishment of parasitoid
populations and the overall impact of
the parasitoids on psyllid populations.
To account for these discrepancies,
we compared the performance of the
parasitoids at coastal and interior sites
that were paired by latitude using three
measures: (1) parasitism rates, (2) the
ability of a single wasp to parasitize
psyllids and (3) the longevity of adult
female wasps outdoors.
In the first study, three pairs of
coastal and interior monitoring sites
were sampled in July 2003: (1) Sonoma
and Sacramento counties, (2) Alameda
and Fresno counties and (3) San Luis
Obispo and Bakersfield counties. Two
11.8-inch (30-centimeter) branch tips
were taken from each site and up to
50 nymphs from each sample were
dissected to check for parasitism. We
found that the average parasitism rate
at coastal sites (Sonoma, Alameda and
San Luis Obispo counties) (29.7% ± 6.6%)
was significantly higher than the average
parasitism rate (1.2 ± 0.9%) at the interior
sites (Sacramento, Fresno and Kern coun-
ties) (t-test, P < 0.05, n = 8).
In a second study, three to four mesh
sleeve cages were fixed to river red
gums at two paired sites (Alameda and
Sacramento counties) in July 2003. These
sites represented the coastal and interior
temperature regimes at the same lati-
tude; mean average and high tempera-
tures for the cities of Berkeley (Alameda
County) and Sacramento (Sacramento
County), where the study was con-
ducted, are 63°F and 71°F, and 74°F and
91°F, respectively. Approximately 100
psyllid eggs were placed in each cage,
and the resulting nymphs then settled
on leaves and began feeding. When the
psyllids had reached the third instar, a
single female wasp was released into
each cage. The cages were removed from
the field 2 weeks later and all psyllids
inside were dissected to check for para-
sitism. Average parasitism rates in the
cages were far higher at the Berkeley site
(34.1% ± 9.31%) than at the Sacramento
site (1.0% ± 1.0%) (2-tailed t-test, df = 14,
t = 2.145, P = 0.003).
In a third temperature study, we
compared the longevity of adult fe-
male parasitoids held in glass vials at
the sites in Berkeley and Sacramento
during summer 2004. During a period
in June when temperatures were cool
in Berkeley but warm in Sacramento,
the wasps lived significantly longer in
Berkeley (14.9 ± 2.4 days versus 5.8 ± 0.7
days) (2-tailed t-test, df = 3, unpaired
t = 3.182, P = 0.037). During the July and
September test periods, temperatures
were similar at the two sites (with un-
usually cool weather in Sacramento in
that part of July) and the wasps’ longev-
ity was similar at both sites (averaging
12 to 15 days).
The wasps performed poorly in the
Central Valley compared to coastal ar-
eas. Parasitism rates were lower overall
in the field, and individual wasps laid
fewer eggs. A possible explanation for
these differences is the shorter lifespan
of the wasps in the summer heat. In
our experiments on the basic biology
of the parasitoids, we found that they
laid eggs for several weeks in the green-
house, which has mild, cool conditions
similar to the ambient conditions in
Berkeley in the summer. However, in
warmer conditions, the wasps did not
live as long and therefore laid fewer
eggs over their lifetimes. The relatively
poor performance of the wasps in the
summer in the Central Valley, when
psyllid numbers build up to their sea-
sonal peaks, helps explain why we have
observed longer times for wasp estab-
lishment in the interior and, to date, less
impact on psyllid populations.
Parasitoid impact
By 2003, P. bliteus had been recov-
ered at 29 of the 32 sites monitored
throughout the season with sticky traps.
Field-produced parasitoids far outnum-
bered insectary production and, for this
reason, managed releases were discon-
tinued. To provide a geographically
comprehensive summary of parasitoid
establishment, we surveyed 55 former
release sites throughout California
from mid-August through October
The red gum lerp psyllid now appears to be under
control in most coastal regions of California due to
the introduction of a parasitic wasp.

234 CALIFORNIA AGRICULTURE • VOLUME 59, NUMBER 4
2003 (Roltsch et al. 2004). At each site,
15 branch terminals (11.8 to 15.7 inches
long) were randomly collected from
three or more trees. On each branch,
30 leaves were randomly selected and
the numbers of exit holes (round holes
that the adult parasitoid chews in the
lerp when it exits), as well as healthy
and visibly parasitized psyllids, were
recorded by life stage.
Parasitoids were recovered at all but
two of 55 locations (fig. 4). At several
locations, levels of parasitoid activ-
ity, as indicated by the proportion of
large lerps containing exit holes, were
strikingly higher than those found in
2002, several months after the initial
parasitoid releases, using similar sur-
vey techniques. For example, while P.
bliteus was extremely rare at the Solano
County site in 2002 (after two releases
prior to this sampling), in October 2003
the parasitoid was common there. On
average over all sites sampled, there
were parasitoid exit holes in more than
one-fifth (22%) of the large lerps. We
note that while exit holes in the lerps
provide an indication of parasitoid
activity, this may not be as accurate as
dissecting live psyllids to determine
the percentage that are parasitized.
Still, the survey confirms that the re-
leased P. bliteus have established in
almost all regions and that parasitoid
activity appears to be increasing annually.
Future biocontrol programs
The red gum lerp psyllid now ap-
pears to be under control in most coastal
regions of California due to the intro-
duction of P. bliteus. Suppression is best
at coastal sites and lower in some parts
of the Central Valley. Our field and labo-
ratory studies suggest that the hot sum-
mer temperatures found in the interior
regions may reduce parasitoid impact.
Still, as psyllid numbers have dropped,
the defoliation and death of eucalyp-
tus trees due to the psyllid have been
reduced. Of key importance for future
control efforts is the observation that
P. bliteus appears to be well established
throughout California, including the in-
terior locations. Therefore, although cur-
rent P. bliteus densities and parasitism
rates are low in the interior, their impact
may continue to increase there, albeit
more slowly than in coastal regions. We
will continue to monitor the red gum
lerp psyllid and the parasitoid popula-
tions to determine if it will be necessary
to import either heat-adapted P. bliteus
populations or additional Psyllaephagus
species to improve biological control in
California’s interior.
D.L. Dahlsten was Professor (now de-
ceased), K.M. Daane is Associate UC
Cooperative Extension (UCCE) Special-
ist, K.R. Sime is Postdoctorate Researcher,
A.B. Lawson was Postdoctorate Researcher
(currently Assistant Professor, California
State University, Fresno), D.L. Rowney is
Statistician, and J.W. Andrews Jr. is Staff
Research Associate, Division of Insect Biol-
ogy, UC Berkeley; T.D. Paine is Professor,
Department of Entomology, UC Riverside;
W.J. Roltsch is Associate Environmental
Research Scientist, California Department
of Food and Agriculture; J.N. Kabashima is
County Director and Farm Advisor, UCCE
Orange County; D.A. Shaw is Farm Advi-
sor, UCCE San Diego County; K.L. Robb
is County Director and Farm Advisor,
Mariposa County; J.A. Downer is Farm Ad-
visor, UCCE Ventura County; P.M. Geisel
is Farm Advisor, UCCE Fresno County;
W.E. Chaney is Farm Advisor, UCCE Mon-
terey County; C.A. Ingels is Farm Advisor,
UCCE Sacramento County; L.G. Varela is
Areawide Farm Advisor, North Coast Re-
gion; M.L. Bianchi is Farm Advisor, UCCE
San Luis Obispo County; and G. Taylor is
Entomologist, University of Adelaide, Waite
Campus, Australia.
We thank the UC Exotic Pests and
Diseases Research Program, UC Statewide
Integrated Pest Management Program,
Action Mulch, Disney Corp., East Bay
Regional Park District, Los Angeles Zoo,
Rancho Santa Fe Association, Stanford
University Buildings and Grounds
Department, and agencies in the cities of
Huntington Beach, Los Angeles, Torrance
and Redwood City for funding. We thank
Mike Keller, Kerrie Davies and John
Jennings of the University of Adelaide,
Waite Campus, and Christine Stone of the
State Forests of New South Wales facility
in the Cumberland State Forest for help
with foreign exploration. We thank Larry
Costello, David Haviland, Daniel Sullivan,
Rod Sime and Marta Yamamoto for labora-
tory or field assistance.
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