Sound production in Scolytidae: Specificity in male Dendroctonus beetles

J. Insect Physiol., 1972, Vol. 18, pp. 2189 to 2201.

Pergamon Press. Printed in Great Britain

SOUND PRODUCTION IN SCOLYTIDAE: SPECIFICITY IN MALE DENDROCTONUS BEETLES R. R. MICHAEL1 ‘Department

and J. A. RUDINSKY2

of Electronics and Electrical Engineering and 2Department of Entomology, Oregon State University, Corvallis, Oregon 97331 (Received 5 April 1972; revised 28 April 1972)

Abstract-The male stridulatory apparatus of six Dendroctmus bark beetles is described, showing species-specificity especially in the elytral files. Typical male stridulation of D. pseudotsugae and D. ponderosae at the chemostimulus of each female’s attractant and at stress when handled, is found to be distinct and specific when electronically recorded.

INTRODUCTION

IT WAS only recently found that scolytid sound production is communicative behaviour and involves the powerful chemical attractants of some species. The chemostimulus of the attractant of the female Douglas-fir beetle, Den&&onus pseudotsugae Hopk. evokes a male chirp that is acoustically distinct from the stress chirps caused by hand pressure (RUDINSKYand MICHAEL, 1972). This behaviour may be common among those scolytids morphologically equipped for it. It is striking that scolytid attractants are usually produced by the host-selecting sex, e.g. male Ips and female Dendroctmus, and in many species the other sex is able to stridulate upon arrival at the established gallery, to ‘announce’ its presence (BARR, 1969). Stridulation is required for natural entry into the gallery of Ips paracmfusus Lanier ( = confusus Let.) (BARR, 1969) and I. ca2Zigruphu.s (Germ.) (WILKINSON et al., 1967). Surgically silenced beetles were sometimes violently attacked at the entry, indicating that the sound signal helps condition the sexual receptivity of the attractant-releasing beetle. With D. pseudotsugue, male sound at the gallery entry induces the female to negate her attraction of flying beetles of both sexes (RUDINSKY,1968, 1969); this behaviour was also evoked in the laboratory, where male arrestment was inhibited (RUDINSKY and MICHAEL, 1972). Such interactions of auditory and olfactory behaviour are complex, and like chemical ‘primers’ (WILSON, 1963) acoustic signals also may have physiological effects which do not release behaviour. LANIER (1970) h as reported considerable morphological specificity in the stridulatory apparatus of some Ips. For several reasons it is interesting to learn whether scolytid stridulation involves species-specific sounds. Obviously it could be a factor tending toward breeding isolation. Second, the aggregation of bark beetles on suitable hosts is generally accepted to be a result of long-range pheromones 2189

2190

R. R. MICHAELANDJ. A. RUDINSKY

and attractive host volatiles, but we know much less about short-range discrimination especially among beetle species sharing pheromones or host trees. Specific sound signals could reinforce olfactory discrimination or replace it if adaptation occurs after aggregation. Third, sonic regulation of aggregative and antiaggregative pheromones, as exemplified in D. pseudotsugae, seems likely only where somewhat specific signals have evolved. For initial study of this question in male Dendroctonus, the stridulatory apparatus of six species including D. pseudotsugae was examined and measured. We chose species that could be expected not to subject each other to selective pressure for sound specificity. Besides the Douglas-fir beetle, these are the mountain pine beetle, D.ponderosae Hopk. ; the red turpentine beetle, D. valens Let. ; the western pine beetle, D. brevicomis Let. ; the southern pine beetle, D. frontalis Zimm; and the spruce beetle, D. ru$pennis Kirby. Though several of these species are known to share pheromones (PITMAN et al., 1969), and others share a single host species, e.g. Pinusponderosa Laws., none are known to share both pheromones and host attractants. Then we compared acoustic properties of the stridulation of male D. pseudotsqgae to those of D. ponderosae. Though similar in behaviour and almost identical in size, these two species have different hosts and different pheromones. A later phase of our study will involve comparison of the acoustic factor with other possible isolating and discriminating factors (olfactory, ecological, mechanical, etc.) in the behaviour and physiology of closely associated species. MORPHOLOGY OF MALE STRIDULATORY APPARATUS HOPKINS (1909) described the sound organs of male D. vaZens, and LYON (1958) presented a schematic dorsal view of the seventh abdominal segment of various Dendroctonus species. Stridulatory sound or movement by males of D. pseudotsugae (CHAPMAN,1955), D. brevicomis (TATE and BEDARD,1967), and D. ponderosae (MC~AMBRIDGE,1962) has been used for sex identification. This type of stridulatory organ is termed the elytra-abdominal type in contrast to the gula-prosternal type in Scolytus and the more complex vertex-pronotal type occurring in stridulating species of the genus @s (BARR, 1969). Sound is produced by the friction or rubbing together of two specialized structures on the body surface, i.e. the plectrum (sensu Barr) or paired conical processes or scrapers on the median posterior margin of the seventh tergite (Fig. lb-c); and the pars stridens (sensu Barr) or a series of transverse ridges or teeth in a file on the undersurface of the elytra located near the apex and along the sutural margin (Fig. la). When the elytra are locked together, the backward motion of the abdomen engages the processes in the file and the downward motion scrapes them across the ridges producing an audible chirp. Materials and methods From 40 to 80 male specimens of each of the following species were examined: D. pseudotsugae Hopk. from Pseudotsugae menziesii (Mirb.) France, Mary’s Peak,

SOUND

PRODUCTION

IN

SCOLYTIDAR

2191

Oregon; D. ponderosae Hopk. from P&W ponderosa Laws, LaPine, Oregon; D. valets Let. from P. pond&-rosa, Sisters, Oregon; D. rujipennti Kirby from Piceu sitchensis (Bong.) Carr., Yakutat, Alaska; P. ghca (Moench.) Voss., Yukon, Alaska; P. engeZmanni Parry, Cedar Breaks, Utah; D. brewicomis Let. from P. ponderosa, Sisters, Oregon; D. frontalis Zimmer. from Pinus taedu L., Rye, Texas. Right

(b)

Left

icf

FIG. 1. Stridulatory organ of male Dendroctonus, showing (a) the pars stride-m with the file of teeth (F), sutural margin (SM), and winglock (WL). (b and c) The plectrum with processes (P), setose area (SA), spine (S), and sclerotized band (SB).

Male sex was determined in D. pseudotsugae by the absence of strial punctures on the elytral declivity (JANTZ and JOHNSEY, 1964) and in the other species by the presence of the stridulatory processes. Only the left elytron is apparently essential for stridulation (see below); it was detached from the beetle and turned over to expose the file. Ten males taken at random were measured for the distance between processes, the length of the left elytron, the size of the file, the number of ridges in this file, and their distance from each other. Because the distances between ridges in the caudal half vary greatly from those in the cephalic half, the file was divided and each half counted separately. Laterally as well as cephalad the ridges diminish and fade away, so that the measurement of the length and width of the file was to a

2192

R. R.

MICHAEL

AND

J. A. RUDINSKY

small degree arbitrary. To measure the distance between the tips of the spines on the two processes of the plectrum, 650 x magnification was used. This was also necessary for the file of D. frontalis, the smallest species examined. The scanning electron micrographs were made on a Cambridge SEM ‘Stereoscan’ Model S4. Results Certain characteristics were common to all species and certain appeared to be specific. Pars stride. On the left elytron the file of transverse ridges or teeth has a prolonged teardrop or club-like shape, narrowing gradually cephalad (Fig. la; Fig. 2a-d). It extends over the sutural margin onto the right elytron in such a way that the centre of the file coincides with the sutural margin of the locked elytra and is exactly over the centre point between the two processes on the seventh tergite. The file reaches to the ‘wing-lock’ (Fig. la, WL), which is smooth, but beyond it on the right elytron begin short teeth (Fig. Za-d) that appear as an unbroken continuation of the file when the elytra are locked. These teeth on the right elytron are probably seldom used in stridulation as they are far from the median line and thus from the processes. With D. pseudotsugae when the file was excised no stridulatory sound was produced although stridulatory movements occurred, whereas when the wing-lock area with the teeth on the right was excised, chirps were still heard. The teeth of the file are sharp, and sometimes branch into a narrow Y. The distance between ridges is much greater (almost twice) in the lower, caudad half of the file than in the narrower cephalad half. The shape of the teeth and of the file itself is similar among the species examined but significant differences were found in the number of teeth and the distance between them in relation to the length of the file (Table 1). As shown, for example, the number of teeth in D. pseudotsugae is one-third more than in D. ponderosae, though the file length is almost the same, and the distance between teeth is correspondingly smaller in D. pseudotsugae. Scanning electron micrographs of the teeth of six species are shown in Fig. 2 (e-j). It is interesting that the relation between insect body size and the length of the file is usually inverse; i.e. D. vah, the largest Dendroctunus, has a relatively smaller file than D. brevicomis and D. frontalis, the smallest species. Plectrum. The two median stridulating processes or scrapers on the posterior margin of the seventh abdominal tergum of the Dendroctoms species examined agree generally with the schematic presentation of the D. valens processes by HOPKINS (1909). The posterior margin of the seventh tergite is of widened V shape and appears heavily sclerotized because of a strongly sclerotized strip of integument (Fig. lc, SB) near the posterior edge of the tergum, whereas in females the posterior edge is convex and without a sclerotized band. This sexual dimorphism of the seventh tergite has also been used to separate the sexes (LYON, 1958; JANTZ and JOHNSEY,1964; TATE and BEDARD,1967). The scrapers have the form of a truncated cone. The angle of their position in relation to the posterior margin, their dimensions, and degree of sclerotization, are

2193

FIG. 2. Scanning electron micrographs of the right (a) and the left (b) elytra of male D. pseudotsugae and the same (c and d) of D. ponderosae, and details of the file of teeth on the left elytra of (e) D. pseudotsugae, (f) D. ponderosae, (g) D. valens, lines = 7 p. (h) D. obeszts, (i) D. brevicomis, and (j) D. f rontalis. Vertical

2194

FIG. 3. Oscillograms of typical chirps of (a) male D. pseudotsugae in response to an attractive female and (b) to stress when hand held, 13 March and 7 September 1971, 1%19°C. (c and d) Male D. ponderosae in response to an attractive female (double and triple chirp) 2 August 1971, 23°C. (e) Male D. ponderosae in response to synthetic attractants 2 August 1971, 23°C. (f) Male D. ponderosae in response to stress when hand held 15 July 1971, 23°C.

D. frontalis

(2.;$6)

(2.:1:.7)

(3.;1:.6)

(3.Z.4)

(4.Z.9)

(3.G.9)

(3:$2)

(3pd_6.6)

0.26 d (0.25-0.27)

(5270)

(3::7)

(4Z64)

(262-831)

(3&9)

(3Z7)

(212132)

(2&2)

(384-351) (273-137)

Lower half

1)

(6%3)

(7:8_as3)

(Z57)

(6%)

(7?l?

(f%7)

Total

No. of teeth on file Uhty?

(427)

(4Z.O)

(7.;%6)

(5.&3)

(9.:-9’:.0)

Total

0.43 c (0.42-O-49) (2.;1:*6)

(4Z.8)

0.68 b (0.52-0*86) (4.zl.l)

Il.2 (9-14)

(6?k)

O-65 b (0.59-0.74)

(10~;%9) (7X%)

(7.89-;30.6)

0.86 a (0.74-0.92)

Lower half

0.67 b (056-0+32)

“TpYF

File length (mm)*

* Different letters indicate significant difference at P
D. breoicomis

D. pseudotsugae

D. ponderosae

D. ruj?pennis

D. valens

Species

Elytron length (mm)

Distance between teeth (p)

TABLE I-MORPHOLOGICAL DIFFERENCESIN THE MALE STRIDULATORYAPPARATUSOF SIX Dendroctonus

260 e

180d

161 d

109c

132b

87a

Ratio of number of teeth to length of file

SPECIES

(2‘?27)

(4%)

Distance between processes (cl) -

“z

$

2

0”

2196

R. R. MICHAELand J. A. RUDINSKY

shown in Fig. l(b-c, P). The base is anchored in a heavily sclerotized band near the posterior edge of the tergite and is strongly sclerotized but the sides of the scraper are only slightly sclerotized. From the base of the scraper through the centre runs a channel or tunnel which is open into the integument and without sclerotization at the base, but which widens like a funnel at the end. This end bears a stout, short spine (Fig. lc, S) imbedded into the heavily sclerotized posterior edge but protruding noticeably from it. This edge is prominent and inclined toward the abdominal tergite in such a way that-seen from above-the root of the spine is covered and only its tip is seen. Among the species examined, there are interesting differences in the size of scraper as well as in the degree of sclerotization. In D. eralens, which is the largest species, the scrapers are relatively smaller and much less sclerotized than those in the smallest species, D. frontalis and D. brevicomis. In addition, the distance between scrapers varied in some species (Table 1). The paired setose areas (Fig. lb, SA) on the seventh segment were believed by some older authors (reviewed by BARR, 1969, p. 659) to be part of the stridulatory apparatus. However, in D. pseudotsugae and D. ponokosae they are more than 300 p apart and during stridulatory movement they bypass the file by quite a distance on each side. When the flying wings are folded under the elytra, they cover only the anterior part of the seventh tergite and the posterior portion is free to engage the file. When the flying wings are being folded after landing, no sound occurs and there is no stridulatory movement of the abdomen. Stridulation has been observed to occur while the beetle is walking. During sound production the male D. pseudotsugae first moves its abdomen posteriorly toward the elytral declivity until it engages the ridges at the narrow end of the file and then moves rapidly down. One downward movement produces one chirp. To begin another chirp the beetle retracts the abdomen away from the file, moves it slightly upward and backward toward the file before pulling the scrapers downward again in another chirp. ACOUSTIC PROPERTIES OF MALE STRIDULATION Certain acoustic properties of the stridulation of male D. pseudotsugae were shown previously (RUDINSKYand MICHAEL, 1972). Now we have compared them to tbe same properties of stridulation by male D. ponderosae. This species was chosen because it has almost the same size and proportion as D. pseudotsugae, so that body size is not a factor in specificity. Also the plectra and elytral files of both species were found to be quite similar but the teeth were considerably different. Thus it possibly afforded a demonstration of the relationship between morphological and acoustic specificity in Dendroctonus. The chemically induced behaviour of both species is similar enough to allow the same kind of study of the interaction of olfactory and auditory response as was already done with D. pseudotsugae. The onomatopoetic term ‘chirp’ has always been used by forest entomologists to describe the male Dendroctonus sound. We use it also in the sense of BROUGHTON

SOUND PRODUCTION IN SCOLYTIDAE

2197

(1963) for ‘the shortest unitary rhythm element of a sound emission that can be readily distinguished as such by the unaided human ear’. MateriaZ-s and methods

Electronic equipment and techniques in recording were as described previously (RUDINSKYand MICHAEL, 1972). A Hewlett-Packard Model 15119 A condenser microphone, a PAR Model No. 113 low-noise preamplifier with bandwidth set at 300 to 100 kHz, and an Ampex Model FR-1300 tape recorder operated in the FM mode at 60 in./sec were used. Overall bandwidth is believed to adequately accommodate the observed spectrum. Oscillograms were recorded by first establishing a cueing track on the tape to initiate a single oscilloscope sweep just prior to onset of the signal. Polaroid photographs of temporally distributed chirps were made from a Tektronix Type 565 dual beam oscilloscope at a tape speed of 7i in./sec. Beetles tested for both sound production and response to attractants came from naturally infested Douglas-fir or ponderosa pine logs from western and eastern Oregon respectively. The logs were stored at 4°C and brought to beetle emergence temperature as described by RUDINSKY(1963). At least 3 to 5 healthy individuals were recorded sequentially in each test situation as described by RUDINSKYand MICHAEL (1972), i.e. stress stridulation with the beetle’s head and thorax held securely and premating stridulation both with the male near the entrance of an attractive female gallery in the bark and with the male alone but stimulated by natural and synthetic attractants in the olfactory walkway used previously (JANTZ and RUDINSKY,1965). In the tests of chemostimulus of sonic response during the typical arrestment and klinotactic (WOOD et al., 1966) behaviour in this walkway, stridulation was noted as such without regard for increases in volume or number of chirps before a pause. In order not to confuse male sound response to stress with the response to the test attractants, which could not be distinguished by ear, we handled the beetles slowly, gently, and as little as possible. They were allowed to climb onto a rod or stick for transfer to the walkway, where they climbed off, rather than being held with tweezers. Those which fell on their back (where they usually stridulate) were discounted. The synthetic pheromones used with D. pseudotwgae were frontalin (PITMAN and VITB, 1970; KINZER et al., 1971) 98.5 per cent purity; trans-verbenol (RUDINSKY et al., 1972) 95 per cent purity, both from Chemical Samples Co. ; and 3-methyl-2-cyclohexen-l-one (KINZER et al., 1971) technical grade, from Aldrich Chemical Co., Milwaukee, Wis. With D. pcmderosae trans-verbenol (PITMAN et al., 1968) was used. Host monoterpenes respectively were camphene 98% and alphapinene 95% from K and K Laboratories, Inc., Plainview, N.Y. All were diluted to needed concentrations in 95% ethanol. For analysis of variance in the properties of stridulation by each species, ten photographs each of male sounds at hand pressure, at female attractants including synthetic forms, and at the gallery entrance of a live attractive female in a log were

2198

R. R. MICHAELANDJ. A. RUDINSKY

selected at random from tapes totalling over 4440 chirps for D. pseudotsugae and 2000 chirps for D. ponakrosae. The sound properties analysed were the number of toothstrikes per chirp, duration of chirp, and strike rate per sec. Results It was established that, like D. pseudotsugae, D. ponderosae males also stridulate in response to the chemostimulus of the female attractant (Table 2). Besides transverbenol there are unidentified minor components of the natural attractant of D. p0nderosa.e (PITMAN et al., 1968). These were not tested and may account for the significantly greater sound response to frass than to the next most effective treatment, trans-verbenol and ponderosa pine resin. The tactile and visual stimuli of the bark and entry may also be important. TABLE 2--RESPONSE OF 60 UNFEDMALED. ponderosae TO SYNTHETICATTRACTANTS IN THE OLFACTORY WALKWAY No. of beetles that Attractant components

Stopped

Stridulated

Complete attractant (female frass) trans-Verbenol (0.1%) + resin (0.5%) trans-Verbenol + alpha-pinene (0.1%) trans-Verbenol alone Resin alone Alpha-pinene alone 95 y0 ethanol (control)

60 a 48 a 31 b 2c 22 b 19b oc

60 a 26 b 15 c Od 19 b c 16c Od

Each beetle was tested alone. All substances were diluted to indicated percentages in 9.5% ethanol. * Different letters indicate the difference is significant at P~0.01.

With D. pseudotsugae, as earlier reported (RUDINSKY and MICHAEL, 1972), we evoked male chirps without significant difference in acoustical properties whether the stimulus was the natural attractant female frass or four synthetic components. When a live female was in the log with attractive frass over which the male was arrested, the rate of toothstrikes/sec was still the same, but the chirp was longer and more teeth were struck than when the stimulus was the chemical attractant alone. All of these attractant chirps were different from the stress chirp when the beetle was hand held (Fig. lc-f in RUDINSKY and MICHAEL, 1972). These similarities and differences of tested sound properties are shown in Table 3. Typical chirps at stress and at the attractive female are shown in Fig. 3(a-b). With D. ponderosae, the correlation between the distinct male chirps evoked by the known synthetic components of the attractant (frass was not tested) and an attractive female in a log was comparable to the correlation found with D. pseudotsugae. More than half of the chirps evoked by the synthetic attractants were single

2199

SOUNDPRODUCTION IN SCOLYTIDAE

TABLE ~-DIFFERENT PROPERTIES OF MALE D. pseuabsugae STRIDULATION AT STRESS IN HANDLINGAND AT VARIOUSATTRACTANT STIMULI,RECORDED AT 18-19°C Properties of sound response* No. of toothstrikes/chirp

Chirp duration (set)

Rate (toothstrikes/sec)

Stimulus

Range

Mean

Range

Mean

Range

Mean

Stress Frass Synthetic attractants+ Females in log

52-67 14-30

58.60 a 22.70 b

0*053-0.097 0~019-0~061

0.0681 a 0.0364 b

680-1088 488-832

882 a 643 b

12-34 26-61

23.90 b 39.00 c

0,020--0.049 0*033-0*108

0.0353 b 0.0691 a

536-960 384-768

690 b 588 b

* Means followed by same letter not significantly different at P < 0.01. tram-verbenol, camphene in ethanol.

t Frontalin, methylcyclohexenone, and

uninterrupted, i.e. obviously different from the double (sometimes triple) interrupted chirp evoked by the attractive female in a log. This is borne out by statistical analysis (Table 4). However, the interrupted chirps from both stimuli were very similar (Fig. 3c-e). It is not known whether this difference reflects TABLE

~--DIFFERENT PROPERTIES OF MALE D.ponderosae STRIDULATION AT STRESS IN HANDLING AND AT VARIOUS ATTRACTANT STIMULI, RECORDED AT 22-23°C

Properties of sound response* No. of toothstrikes/chirp

Chirp duration (set)

Rate (toothstrikes/sec)

-

Mean

Stimulus

Range

Mean

Range

Mean

Range

Stress Synthetic attractantst Females in log

25-38

30.2 a

0*0251-0060

0.0384 a

5.50-990

84Oa

16-33 12-52

25.4 a 24-S a

0~0149-0~040 0~095-0~185

0.0247 a 0.143 b

700-1610 113-480

1096 b 238 c

* Means followed by same letter not significantly different at P
the effect of tactile and visual stimuli present on the log but absent in the plastic walkway used with the synthetic attractants, or the unidentified pheromone components not used in the walkway. Further tests will be made with the complete pheromone when available. Stress sound (Fig. 3f) differed significantly from both attractant chirps in rate, and from stridulation near a live female in rate and duration (Table 4). It is not known how the interrupted chirp is made. Apparently

2200

R. R.

MICHAELAM)J. A. RUDINSKY

the abdomen is momentarily very slightly retracted so that the plectrum is disengaged from the file or a hesitation occurs in the motion. The sonic response of male D. ponderosae to the attractive female is so different in the shape or ‘envelope’ of the chirp from that of D. pseudotsugae that specificity was apparent even before statistical analysis. That is, D. ponderosae has many interrupted chirps and D. pseuabtsugae does not. In addition, according to the significant differences in chirp duration and rate, the D. ponderosae male stridulates longer and more slowly. The number of teeth struck is not significantly different during the attractant chirp of each species. This is a result of the fact that D. pseudotsugae uses about one-third of the total teeth on the file in the attractant chirps but in stress chirps uses over one-half (Tables 1, 3) and D. pmderosae uses about one-half of its total file with all stimuli tested (Tables 1, 4). The reason for these differences in the number of teeth struck by D. pseudotsugae is not known. Similar differences in recorded sounds of various species of Berosus beetles were reported by VANTASSELL(1965). The stress chirps of each species differ significantly in number of toothstrikes and in chirp duration but not in rate (which is greater than with either attractant chirp). The differences correspond to the greater number of teeth on the file of D. pseudotsugae (Table 1). Since the teeth in D. pse-udotsugae are about half as far apart as those in D. ponderosae, the abdominal movement must be faster in D. ponderosae to give the same rate of toothstrikes in both species. Such stress sound may be more or less phonokinesis and have little behavioural or isolating importance. With these two species the consistent differences in recorded sounds appear to be related to the described morphological differences in the pars stridem rather than those in the plectra. That this may be found also in the other species is suggested by the fact that the files of teeth are capable of greater variety than the scrapers and in the examined species they show greater differences. It is clear that considerable species specificity exists in the sound-producing apparatus of the male Dendroctonzls beetles. With D. ponderosae and D. pseudotsugae this specificity results in species-specific sounds. Acknowledgements-We thank the Silviculture Laboratory, U.S. Forest Service, Bend, Oregon, for help in obtaining D. ponderosue and R. B. &kTJmsoN, Oregon State University Computer Center, for the statistical analyses. The scanning electron micrographs were made by Electros Analytics, Tigard, Oregon. This research was supported by the Oregon State University Research Foundation and this is O.S.U. Agricultural Experiment Station Technical Paper No. 3308.

REFERENCES

BARRB. A. (1969) Sound production in Scolytidae (Coleoptera) with emphasis on the genus Ips. Can. Ent. 101,636-672.

BROUGHTON W. B. (1963) Method in bio-acoustic terminology. In Acoustic Behavior of Animals (Ed. by BUSNEL, R. G.), pp. 3-24. Elsevior Press, New York. CHAPMAN J. A. (1955) Sex determination by stridulation sounds in the Douglas-fir beetle, Dendroctonus pseudotsugae.

B&Mm.

Prog. Rep. Div. Forest Biol., Ottawa

11,2.

SOUNDPRODUCTION IN SCOLYTIDAE

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HOPKINS, A. D. (1909) Contributions toward a monograph of the scolytid beetles-I. The genus Dendroctonus. U.S. Dept. Agric. Bur. Ent. Tech. Ser. 17, Part I. JANTZ 0. K. and JOHNSEY R. L. (1964) Determination of sex of the Douglas-fir beetle Dendroctonus pseudotsugae Hopkins (Coleoptera: Scolytidae). Can. Ent. 96, 1327-1329. JANTZ0. K. and RUDINSKYJ. A. (1965) Laboratory and field methods for assaying olfactory responses of the Douglas-fir beetle, Dendroctonus pseudotusgue Hopkins. Can. Ent. 97, 935-941. KINZER G. W., FENTIMANA. W., Jr., FOLTZ R. D., and RUDINSKYJ. A. (1971) Bark beetle attractants: 3-methyl-2-cyclohexen-l-one isolated from Dendroctonus pseudotsugae. J. econ. Ent. 64, 970-971. LANIER G. N. (1970) Biosystematics of North American Ips (Coleoptera: Scolytidae) Hopping’s group IX. Can. Ent. 102, 1139-1163. LYON R. L. (1958) A useful secondary sex character in Dendroctonus bark beetles. Can. Ent. 60, 582-584. MCCAMBRIDGE,W. F. (1962) Sexing Black Hills beetles, Dendroctonus ponderosae Hopkins. Ann. ent. Sot. Am. 55, 723-724. PITMAN G. B., VITB J. P., KINZER G. W., and FENTIMANA. F., Jr. (1968) Bark beetle attractants: trans-verbenol isolated from Dendroctonus. Nature, Land. 218, 168-169. PITMANG. B., VITO J. P., KINZER G. W., and FENTIMANA. F., Jr. (1969) Specificity of population aggregating pheromones in Dendroctonus. J. Insect Physiol. 15, 363-366. PITMAN,G. B. and VITB J. P. (1970) Field response of Dendroctonuspseudotsugae (Coleoptera Scolytidae) to synthetic frontalin. Ann. ent. Sot. Am. 63, 661-664. RUDINSKYJ. A. (1963) Response of Dendroctonus pseudotsugae Hopkins to volatile attractants. Contr. Boyce Thompson Inst. PI. Res. 22, 22-38. RUDINSKYJ. A. (1968) Pheromone-mask by the female Dendroctonus pseudotsugae Hopk., an attractant regulator. Pan-Pacif. Ent. 44, 248-250. RUDINSKYJ. A. (1969) Masking of the aggregation pheromone in Dendroctonus pseudotsugae Hopk. Science, Wash. 166, 884-885. RUDINSKYJ. A., KINZERG. W., FENTIMANA. F., Jr., and FOLTZR. L. (1972) Trans-verbenol isolated from Douglas-fir beetle: laboratory and field bioassays in Oregon. J. enaironmental Ent. 1. RUDINSKYJ. A. and MICHAELR. R. (1972) Sound production in Scolytidae: Chemostimulus of sonic signal by the Douglas-fir beetle. Science, Wash. 175, 1386-1390. VAN TASSELL E. R. (196.5) An audiospectrographic study of stridulation as an isolating mechanism in the genus Berosus (Coleoptera: Hydrophilidae). Ann. ent. Sot. Am. 58, 407-413. TATE N. L. and BEDARDW. D. (1967) Methods of sexing live adult western pine beetles. r. econ. Ent. 60, 1688-1690. WILKINSONR. C., MCCLELLANDW. T., MURRILLO R. M., and OSTMARKE. 0. (1967) Stridulation and behavior in two southeastern Ips bark beetles (Coleoptera: Scolytidae). FL Ent. 50, 185-195. WILSON E. 0. (1963) Pheromones. Sci. Am. 208, 100-114. WOODD. L., BROU~NEL. E., SILV~R~TEINR. M., and RODINJ. 0. (1966) Sex pheromones of bark beetles-I. Mass production, bioassay, source, and isolation of the sex pheromone of Ips confusus (LeC). J. Insect Physiol. 12, 523-536.