Paper Number 4
USE OF PHEROMONE TRAPS TO SUPPRESS POPULATIONS OF SCOLYTUS
MULTIS TRIA TUS 1
IN SMALL, ISOLATED CALIFORNIAN COMMUNITIES2
By
C.
MARTIN
BIRCH
Department of Entomology,
Vniversity of California,
Davis 95616
Dutch elm disease was first discovered in California in
1975 and the State of California has since been involved
in a program to eliminate all sources of infection from
the counties where the disease has been located (Arciero
1979). However, the State is also funding research to develop methods for suppressing the fungus and vector,
should the disease become more widely established in
California, in the future. One of these methods is a trapping system using pheromone-baited
traps to remove
large numbers of the smaller European elm bark beetle.
Scolytus multistrio,tus (Marsham), from cities such as Sacramento, which have large numbers of valuable elms.
Pheromone-based trap-out programs have been used
previously with the Scolytidae: to reduce a population of
the western pine beetle, Dendroctonus brevicomis LeConte,
in California (Wood and Bedard 1974), and in several
studies with S. mullistriatus (Cuthbert, Peacock and Cannon 1977; Cuthbert and Peacock 1979; Lanier 1979).
However, these other studies with S. mullistriatus have
been conducted in complex environments where elm
trees were widely distributed both inside and outside the
study areas, and where Dutch elm disease was prevalent.
This study is being conducted in a unique area where
the towns form virtual island populations of elms surrounded by desert, and where Dutch elm disease does
not occur. We are thus looking at the effectiveness of
pheromone trapping in an optimal setting, i.e., without
the complication of the disease and without the problems
of beetle migration to and from surrounding populations. The data presented are from studies conducted in
1976 and 1977. Further research will continue at least
until the end of the 1978 flight season.
The study is being conducted in the towns of Big Pine,
Independence
and Lone Pine, in the Owen's Valley,
California (Birch et al. 1977). The valley is 1200m above
sea level on the eastern border of the State and is bounded
to the west by the Sierra Nevada Mountains and to the
east by the White Mountains, both rising to over 4300m.
The three towns are distinctly separated from one another by semi-desert, covered with scrub vegetation.
die-back of small branches, but a few are in. very poor
condition and harbor large broods of S. multistriatus.
Trapping Design
Cardboard sheets (45 x 56 em) were fastened to telephone or power poles 3 m above ground, coated with
Stikem Specialill, and a multilure bait stapled in the center of each trap. In 1976, two types of bait were compared: Conrel~, where the compounds elute from capillary tubes open at one end, and Herconill, where the
pheromone is impregnated in a laminated plastic formulation. Both types were designed to release the components of multilure at the following rates: cubebene,
800,...glday; heptanol, 400,...glday; multistriatin, 100,...gI
day. Both baits were designed to release pheromone for
80-90 days, but in these tests they were replaced every
50 days to allow for a margin of safety.
A different pattern of trap deployment was used in
each town. In Independence,
52 traps were spaced as
evenly as possible in a grid pattern throughout the town.
The total area covered by the grid was about one km·.
Conrel and Hercon baits were alternated between traps.
Traps were placed without regard for their proximity to
elm trees. In Lone Pine, 30 traps were placed round the
perimeter of the town and four in the center. In 1976,
single and double traps (two trap surfaces stapled side by
side with a single bait) were placed alternately round the
perimeter. In 1977 only single traps were used. In Big
Pine, traps were set out in four lines of six traps, one line
on each side of town.
Besides the regular trap changes in Independence, 10
traps and baits were replaced more frequently-every
25
days in 1976 (i.e., once between regular trap changes)
and every 7-10 days in 1977.
Large numbers of elms are present in all the towns.
They are a mixture of English elm (Ulmus procera Salisbury), Siberian elm (U. pumila L.) and hybrids of these.
The majority of trees are healthy, exhibiting only minor
Traps were also put up along the main highway linking the three towns. They were located every 3.2 km between Independence and Lone Pine, and every 8 km between Independence and Big Pine. These traps were
replaced at the same time as those in the towns. Traps
were also placed well away from known elm trees at varying distances (and elevations) from the three towns.
Among these were traps 8.0 km east and west of Lone
Pine and Independence, and a trap at 2745 m elevation
in the Sierra Nevada.
Coleoptera:Scolytidae.
'Supported by a grant from the Stateof California.Departmentof
Food and Agriculture. and conducted under a cooperati\'e research 381.:eementwithtlie USDAForestService.NortheasternForestExperimentSta·
tion-Research
WorkUnitNE·2209.Thisprojecthasinvolvedtheconpera·
tion of a large number of indi\'iduals and organizations. I would like to
acknowledge
thecontributions
of R. W. Bushing.P.Callery.S. L. Clement.
./. c. Millerand T. D.Paine.and especiallythoseof '.C.M.and T.D.P.tn
thismanuscript.R. W.Bushingwasresponsiblefortliesubsampling
methodology.was1O,'ohed10muchof tile onginalexpenmentaldeSIgn.and
ga"econtinuedIOvaluable
inputunlllhisuntimelydeathin August1978.
• Supplementtnthe firstprogressreporton thISprojectforthepenod
endingOer.~1. )976.
At trap change, the old traps were returned to the laboratory where all S. multistriatus were counted. A subsampIing procedure developed by R. W. Bushing3 accounted
for 98% of the variation in the actual counts, and required that only a fraction of the trap surface be counted .
All trap catch figures are underestimates of actual mortality. since early in a trapping period Stikem (plus beeties) tends to drip from the traps and later the Stikem
.
.
'.
'.
becomes drIer, covered WIth debrIS and less effectlve.
I
] 12
© 1979 Entomological Society of America
0013-8754/79/0101-1204$00.75/0
Vol.25,/10.1
ESA
1979
BULLETIN
Table I.-Total
number of Scolylus mullWrialus captured on pheromone-baited traps located within towns,
Owen's Valley, California, 1976 and 1977.
Number of beetles captured
Year Lone Pine Independence
Big Pine
Total
1976
1977
323,059
57,386
223,706
71,182
49,229
34,359
595,994
162,913
Totals
380,445
294,888
83,588
758,907
Table 2.-Rate of Scolylus multis/ria/is capture on pheromOlw-baited traps located within towns, Owen's Valley,
Calilclfllia, 1976 and 1977.
RateD of beetles captured
Year Lone Pine Independence
Big Pine
All towns
1976
1977
62.1
8.7
28.]
7.0
13.4
10.4
35.4
8.2
Ratio
19761
1977
7.1
4.0
1.3
4.3
• Ratt' is ('xpn'sst'd in It'rms of mean number of bee des captured per tTap
pt"T da)'. 'fht'rt,
W('rt' .34 tTaps in Lone
Big Pin •. During th,' third lr.pping
nap!! \\'t'fl' monitored.
Pine, 52 in Independence
and 24 in
inten·a. in B!g Pine. 1977. only four
Trapping Results
Almost 759,000 beetles were trapped in the three
towns over the two year period (Table I). Overall, the
1977 total was less than one quarter of ] 976, with the
biggest reduction in catch occurring in Lone Pine. Catches
between towns and years can be compared more readily
if beetle catch is expressed as the number of beetles
caught on each trap per day, since the number of traps
and the number of trapping days differed in each town.
On this basis, the reduction in trap catch is seen to be
even gTl'ater in Lone Pine Crable 2). The 1977 figure for
Big Pine is not strictly comparable, since during the last
trapping period of 1977 all traps, except four, were removed to reduce the trapping pressure in that town.
In 1976, no significant difference could be determined
between Conrel and Hercon baits or between single and
double surface traps, although double traps consistently
trapped slightly higher numbers of beetles.
The trend in trap catches is dearly seen in the 10 traps
changed at more frequent intervals over both years in
Independence (Fig. I). Since the catches are computed
as beetles caught on a trap/day basis, the heights of the
bars (trap catches) can be directly compared even thougb
the widths (days between trap changes) vary. The largest
pt'aks in 1976 and 1977 occur at the same time of year.
It is probable that the early flight was missed in 1976
because the first traps were not put in place until midMay. The April-May and July-August trapping peaks re!len two periods of beetle flight which, in turn, suggests
that two generations are produced each year in this location.
In LOlW Pint" the trap catches became lower as the
year progressed in 1976. In 1977, trap catches for the
first period were very low and increased throughout the
year, although the highest of these was still only half of
the lowest in 1976.
The traps along the highway between Independence
113
and Lone Pine averaged one beetle per day on each trap
during 1976, and 0.2 beetles per trap during 1977. Surprisingly there was no clear relationship between the distance of a trap from either town and its catch. The total
catches on the trap mid-way between these towns was 141
beetles in 1976 and 50 in 1977. The traps between Independence and Big Pine caught only O.I beetleltrap/day
in 1976 and even less in 1977. These low catches confirm
the earlier assumption that the populations of S. mul/istria/us in these towns are relatively isolated.
All the traps distributed in the valley in ] 976 caught
some beetles. The numbers were not as high as those
captured along the highway. For example, the trap 8.0
km east of Independence caught a total of 30 beetles,
that at Onion Valley (2745m), two beetles. Many of these
were at least 8.0 km from any known elm, as were many
of the traps along the highway. It is possible that some of
these beetles were transported on the truck carrying
pheromone baits, but these catches are also an indication
that beetles can fly further than previously thought.
Population Reduction
Trap catches (Tables I and 2, Fig. I) declined dramatically in 1977 in all three towns. Also, in Big Pine where
most of the traps were removed late in 1977, trap catches
on the remaining traps immediately increased. However,
the success of the trapping program depends on either
reducing the population size of S. mullis/ria/us or of reducing damage to elms. Since, without Dutch elm disease
the damage to elm trees is not easily measured, we attempted to estimate the numbers of beetles available to
be trapped.
In 1976, S. mul/is/riatus were trapped live, coated with
a fluorescem powder and released in Independence in
an attempt to use the mark-release-recapture
method for
estimating population size. Of two batches of beetles released (totaling about 20,000). about !4 of I % were recaptured. Catches were distributed throughout the entire grid pattern of traps except for those located in the
extreme east or south areas of the town. The extremely
low recapture rate did not allow for any estimates of population size and in view of the reduction in viability of
beetles coated with fluorescent powder, this method was
not cominued further in the field. Developmem of a
marking system that will eliminate beetle handling is a
high priority in 1978.
Beetles emerge from two sources: elm wood in log
piles and dead, or partially dead limbs, in standing elms.
In 1976,4 log piles were sampled in detail in Lone Pine.
It was determined, from emergence holes in logs, that by
late August over 248,000 S. mullis/ria/us had emerged,
with some larvae. pupae and callow adults still remaining
in the logs. This number equals 72% of the beetles
caught in Lone Pine throughout the season. Since the
number of log piles in Lone Pine is probably ten times
the number sampled. log piles are clearly an imponam,
if not the major, source of beetles. A preliminary survey
conducted in Independence in 1977 revealed almost 100
woodpiles. In one pile, 33 of 65 logs had been attacked.
with a mean density of emergence from the attacked logs
of 4411OOcm'. This emergence density is high compared
to eastern studies (Cuthbert et aI., 1977), and the high
value of 17711OOcm' recorded in this study is even higher
than that normally encountered in the east.
Until mid-1977 the elm trees in all 3 towns were generally healthy. Those that die are on lots where the ownership has changed and where they appear to have been
deprived of surface watering. There are 505 elm trees in
Vol. 25, no. 1
ESA BULLETIN
114
1979
75
~YM
multistriatus trap catches
Independence
60
>-
<I:
Cl
'6:-
45
<I:
a::
f-
""1><
30
15
- - -1977
o
May
June
July
Aug.
Sept.
Oct.
1976
April
May
June
July
Aug.
Sept.
Oct.
1977
FIG. I.-Trap
catrhes of Srolylus mullislriatus on 10 traps in Independence. 1976 and 1977. Based on catrhes from
tht'samt' 10 traps sampled from May ]976 to late 1977. The broken lines indicate the mean catch per trap for all
52 traps in the town each year.
Independence with a breast height diameter above 10
cm. A biased sample of these trees was conducted with a
preference for trees containing significaIll dead wood
(28 trees). It is not possible to describe limbs simply as
dead or alive. infested or unifested. as some limbs have
strips of living tissue running out to a single green branch.
while many large limbs die and arc never infested by S.
1I1IIltislrialllS. Approximately 33% of the trees sampled
showed evidence of previous anack with a mean emergence density of 34/100 cm2• while 20% of the trees sampled mntained brood. This suggests that very few standing trees mntribute to the overall beetle population.
especially since the biased sample coIllained all trees having obvious potential brood material.
Thus. in order to assess the effect of beetle mortality
due to trapping on beetle populations. the size of the
beetle population must be determined with some degree
of accuracy. This will be attempted in Independence
throughout the 1978 trapping period. both in log piles
and standing trees, and (optimistically)
proved mark-release-capture
technique.
usmg an un-
Prognosis
The decline in trap catches in all three towns in ] 976.
and the much reduced trap catches in 1977, althouKh
increasing through the year, are the most apparent trends.
However, the influence of the pheromone trapping on
these trends is at present only correlative: it has not bet'n
shown to be causative. If the decline in trap catches continues through the 1978 trapping period in Independence and Lone Pine, wht're trapping prt'ssure remains
intense compared to Big Pine. and if the trap catch in
Independence can be shown to be a substantial proportion of the inflight beetle population. this tedlllique will
have been demonstrated to have excellt'nt potential. It
could then be used as a prophylatic measure in other
California cities to reduce elm damage due to S. mullislriatus both before and after Dutch elm disease arrives.
Vol.25,IIO.l
ESA BULLETIN
1979
REFERENCES
CITED
Arciero, M. F. 1979. Use of multilure-baited
traps in the
California
Dutch elm disease program
for survey
and detection of Scolytus mullistriatus. Bull. Entomol.
SOL Am, 25: 119-121.
Birch, M. C., R. W. Bushing, T. D. Paine, S. L. Clement,
and P. D. Smith. 1977. Pheromone
traps to suppress
populations
of the smaller European
elm bark beetll'. California
Agr. 31(11):4-6.
Cuthbert,
R. A., and J. W. Peacock.
1979. The forest
service program
for mass trapping
of Scolytus multistriatus. Bull. Entomol. Soc. Am. 25: 105--108.
115
Cuthbert,
R. A., J. W. Peacock and W. N. Cannon, Jr.
1977. An estimate
of the effectiveness
of pheromone-baited
traps for the suppression
of Scolytus
multistriatus (Coleoptera:
Scolytidae). J. Chern. Ecol.
3:527-537.
Lanier, G. N. 1979. Protection
of elm groves by surrounding
them with multilure-baited
sticky traps.
Bull. Entomol. Soc. Am. 25: 109-111.
Wood, D. L. and W. D. Bedard.
1974. Programs utilizing
pheromones
in surveyor
control. Bark beetles-the
western
pine beetle. p. 441--449. In M. C. Birch,
(ed.) Pheromones.
Elsevier North-Holland,
Amsterdam.