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Calling behaviour in female Trogoderma granarium Everts (Coleoptera: Dermestidae)
CALLING BEHAVIOUR IN FEMALE TROGODERMA GRANARIUM EVERTS (COLEOPTERA: DERMESTIDAE) L. HAMMACK* Stored Product Department
and Household of Entomology,
and W. E. BURKHOLDER
Insects Laboratory. Agricultural Research. SEA, USDA. University of Wisconsin. Madison. WI 53706 U.S.A.
(First recrirrd
3 October
19801
Abstract--The effects of photoperiod. insemination, and age on the calling and mating activities of Trogodrrrna granurium females were investigated. Among mature virgin females held on 10: 14. 12: 12. or 16:8 LD. some calling behaviour was observed throughout photophase but 75”,, or more females were active for a period lasting about 8 hr/day. Under all three light regimes. this period was centred around the middle of photophase when virtually IOO”, of females assumed the calling posture. Correlated with diurnal fluctuations in female calling. mating frequency was higher towards the middle as compared to the start of photophase. In contrast to virgins. only increases in both about 3”,, of recently mated females engaged in calling activity. Significant calhng and female receptivity to mating occurred between the 1st and 3rd days of adult life. but the daily calling pattern of virgin females remained stable between the 4th and 10th days.
INTRODUCTION SEX PHEROMONE release by Trogoderma gkzhrum (Herbst) females is accompanied by characteristic postural activity which can be termed sex pheromone-releasing, or calling behaviour (HA~IMACK et al., 1976). The purposes of this study were to establish the existence of similar calling behaviour in the khapra beetle, Trogoderma granurium Everts. and to investigate the effects of age, insemination, and photoperiod on the calling and mating activities of T. yranarium females. MATERIALS
AND
METHODS
T. yranarium were obtained from stocks maintained at the Pest Infestation Control Laboratory, Slough, England. Larvae were reared on a 7:3 mixture by weight of whole wheat and wheat feed at 30°C and 70% r.h. in a 16 hr light: 8 hr dark (16:8 LD) photoperiod (3 a.m. L:7 p.m. D). Insects were removed from culture as pupae, sexed, and held in various numbers in 9 cm dia Petri dishes lined with filter papers. The dishes were examined at 1 day intervals and beetles having emerged from the pupal cuticle within that interval were ascribed an age of s-1 days. These insects pupate within the last larval cuticle and remain quiescent within the dorsally-split larval skin for up to several days after emergence from the pupal cuticle. Young adults, unless tested on the day of emergence, were removed from the larval cuticle at l-2 or 2-3 days of age. Adult males were held like pupae but in groups of .%lOO/dish. Females were maintained in lots of 25-30/dish, and provided with pleated filter paper strips as previously described (HAMMACK et al., 1976). All experiments were conducted in a test chamber that was maintained at 27.5 & 1°C and 60 + 29:, r.h. The photoperiod in this chamber was either 10: 14 (7 a.m. L:5 p.m. D), 12: 12 (7 a.m. L:7 p.m. D), or 16:8 LD (5 a.m. L:9 p.m. D) as specified below. Insects were transferred to the test chamber during the pupal stadium to ensure exposure to the experimental light regime for at least a 5-day period immediately preceding testing. Light intensity during photophase test periods was about 950 lx. Abdominal elevation, along with concomitant extension of at least the mesothoracic legs, was the criterion used to identify calling behaviour. Females whose calling activity *Present address: Metabolism ND 58105 U.S.A.
and Radiation
Research
Laboratory.
Agricultural
Research.
SEA. USDA.
Fargo.
L.
26
HAMMACK and
W. E. BURKHOLDER
was to be monitored were transferred from dishes to individual 5.0 x 1.5 cm glass shell vials usually 1 day before observation. Each vial was lined with a filter paper disk, and contained a strip of pleated filter paper (about 3.0 x 0.5 cm) to provide a vertical surface for calling activity. The number of females calling was recorded every f hr throughout one photophase interval in the test series described below. A series of three experiments was carried out as follows: (1) The eflect offemale age on calling was investigated on 10: 14 LD by observing the behaviour of 8 groups of 20 females ranging in age from c-1 to l&l 1 days. (2) The efSect of daylength on calling periodiciry was investigated by observing 60, 67 day females held on 10: 14 LD; 5-7 day females held on 12 : 12 LD; and 40, 4-6 day females held on 16 : 8 LD. (3) The effect of mating on culling was investigated on 10: 14 LD by observing 20, 45 day females that had been previously paired with 8-10 day-old males. Mixed-sex pairs had been left undisturbed in filter paper lined, 5.0 x 1.5 cm shell vials for a 19 hr period ending at lights-on time on the day of observation. Both paired and control groups were in this case transferred to observation vials f hr before the first calling records were taken. Vials from which mixed-sex pairs had been removed were retained and, on the day after calling activity was recorded, all vials were inspected for eggs to verify that previously paired females had oviposited. Only those females that oviposited were considered to have mated. (Comparable estimates of the percentage of females inseminated were obtained in preliminary tests in which copulatory success was scored both visually during pairing, and by observing the subsequent ovipositional behaviour of the previously paired females.) In addition, tests were conducted to investigate diurnal periodicity of mating activity and the effect of female age on receptivity to mating. To handle large samples conveniently, mating activity in both experiments was estimated by placing mixed-sex pairs in filter paper lined, 5.0 x 1.5 cm shell vials for 5 min, isolating the females in gelatin capsules (No. 000) containing crumpled black paper, and checking the capsules for eggs 48 hr or more after pairing. Only those pairs that subsequently produced ovipositing females were considered to have mated. In the diurnal periodicity experiment, the mating activity of 5-7 day females paired with 4-6 day males was compared between 1.5 hr intervals beginning 0 and 5.5 hr after the start of a 10 hr photophase. Seventy-five females were paired during each 1.5 hr interval. An equal number of unpaired virgin females of the same age were transferred to oviposition capsules as controls. In addition to scoring the later ovipositional behaviour of both groups, male copulatory attempts were noted during pairing of the treatment group. To investigate the efSect of female age on receptivity to mating, the number of females that oviposited after being paired at l-2, 2-3 or 34 days with 4-13 day-old males was determined. (Groups of 4-6, 9911 and 1l-13 day-old males were equally distributed among the three female age groups.) Five minute pairing periods were all confined to a 1.5 hr interval beginning 6 hr after the start of a 10 hr photophase. Each age group contained 38 females. A control group consisted of 38 virgin females, half 2-3 and half 34 days old when transferred to oviposition capsules. RESULTS
Description
of calling hehaviour
T. granarium females were observed to assume a stationary posture like that of T. glabrum in which the abdomen was elevated and the ovipositor at least partially exposed. A more detailed description of the T. glabrum calling posture was reported previously (HAMMACK et al., 1976). However, unlike groups of T. glabrum females which formed
inactive aggregates when not calling but which became motile and dispersed just prior to the onset of calling, groups of T. granarium females remained aggregated throughout the day. There was no period of locomotory activity preceding calling nor were occasional ovipositor probings like those described for T. glabrum evident. Calling behaviour was not conspicuous upon casual observation of T. granarium aggregates, and its frequency was difficult to determine accurately even upon careful examination. It was for this
Calling
Behaviour
in Female
Trogodermu
grtmurium
TABLE I. EFFECTOF AGE ON THE PHOTOPHASE CALLINGBEHAVIOUROF VIRGIN Trogoderma grmariun~ FEMALES (10: 14 LD)
No. of
Age (days)
females
&l I --2 2- 3 334 445 5 -6 89
20 20 20 20 20 20 20 20
I@-11
Percentage of females calling
Mean calling frequency per calling female ( k SE)*
0
5 80 100 100 100 100 lo0
2.0 Il.2 14.5 15.0 15.8 15.7 16.1
* Based on observations made at + hr intervals total of 21 observations/female.
reason that all tests were conducted easily monitored.
throughout
* 0.8 * 0.7 + 0.5 * 0.5 k 0.8 f0.3
photophase
providing
a
with isolated females whose activities were more
EfSect offemale age on calling and mating behaviours
Eighty per cent of 2-3 day old females were observed to call but little or no activity occurred in younger groups (Table 1). Judging from the number of individuals engaged in calling, however. and especially from the frequency of such behaviour, maximum levels were not reached until 34 days. Thereafter, the calling pattern remained stable until 10-11 days, the oldest age tested. The percentages of females which oviposited after pairing, and were thus considered to have been receptive to mating l-2,2-3 and 34 days after emergence, were 28.9, 86.8. and 76.3x, respectively. (Virgin controls laid no eggs.) Although there was no significant difference between 2-3 and 34 day groups, fewer l-2 day females mated as compared to the combined 2--3 and 3-4 day-old group [P < 0.001, partitioning the overall 1’ into independent comparisons (STEEL and TORRIE, 196011. Diurnal periodicity of calling and mating hehaviours
Photophase calling patterns displayed on 10:14, 12: 12 and 16:8 LD are shown in Fig. 1. Although calling occurred throughout the day, in each case activity was maximal toward the middle of photophase when virtually all females were in the calling position. Regardless of photoperiod, 75% or more females called for an interval lasting about
OLtckxp 0 5
--
0
Hours FIG. 1. Photophase calling patterns
12:12.
and
16:8
LD.
Light
16 8 LD
12 12LD
IO 14 LD
6
after
12
start
of
0I
6
16
photophase
of adult virgin Trogoderma granarium females held on 10: 14. portions of bars represent photophase: dark portions represent scotophase.
28
L.
HAMMACK
and
W. E. BURKHOLDER
8 hr/day, but a stable phase relationship was maintained between this interval and photophase midpoints. Thus, while exposure to longer daylengths had relatively little effect on the intensity or duration of daily calling periods, such manipulation did delay the onset of peak activity relative to lights-on time. The observation that some females were calling at lights-on and lights-off times suggests that some scotophase (dark phase) activity went unrecorded, especially on 10: 14 LD. Judged by ovipositional response, significantly more females mated when they were paired 5.5-7.0 hr (73.3%) as compared with O-l.5 hr (56.0x), after the onset of a 10 hr photophase (P < 0.05, computing the interaction x2 corrected for continuity for a 2 x 2 contingency table (STEEL and TORRIE, 1960)). (None of the virgin controls laid eggs.) There was, however, no significant difference between the two intervals when the percentage of males attempting copulation (90.7 and 94.7%) was considered. This suggests that the observed difference in mating activity was due primarily to diurnal changes in female receptivity to males. Eflect of mating on calling behaviour
Of the 30 females previously paired with males in an attempt to obtain mated individuals, none oviposited prior to the start of calling observations, but 29 had laid eggs between 19 and 48 hr after pairing. None of the virgin controls oviposited. Disregarding the one unfertile female whose mating status was uncertain, 3.4% (l/29) of mated females called during the photophase interval after copulation. This contrasted with 100% of the virgin controls. DISCUSSION Females of three dermestid beetle species including Anthrenusjavipes LeConte (BURKHOLDERet al., 1974), Trogoderma glabrum (HAMMACKet al., 1976), and Attagenus elongatulus Casey (BARAKand BURKHOLDER,1977) have been shown to assume a ‘headstand’ posture during sex pheromone release. Although bioassay tests were not conducted as in these studies, the results presented here are consistent with the assumption that similar postural activity by T. granarium females is indicative of pheromone release. Firstly, increases in both female calling and mating were most obvious between l-2 and 2-3 days after eclosion. Secondly, mating occurred more readily during midphotophase periods of peak calling activity than it did early in photophase before maximal daily calling levels had been established. Finally, insemination resulted in a significant reduction in calling during the photophase interval following copulation. Eventual recovery of calling would be predicted, however, as KARNAVAR(1972) reported that T. granarium females do not lay a full complement of eggs after one mating but remate soon after the first batch of eggs is oviposited. ‘VOELKEL(1924) was the first to suggest that T. granarium females produce a sex pheromone and the first to hypothesize that female behaviour could be used as an indicator of pheromone release. He observed that only virgin females perform grasping movements with their protruded ovipositors and postulated that this activity deposits on the substrate a chemical message serving to attract sexually receptive males. Even though females that we considered to be calling did partially protrude their ovipositors, there was little tendency to contact the substrate with this organ. The behaviour that we studied was thus distinct from that described by VOELKEL (1924). Nevertheless, his suggestion that T. granarium females produce a sex pheromone has been substantiated, although some investigators consider it to be an assembling scent that acts both as a male sex attractant and female aggregant (FINGER et al., 1965; ADEESANet al., 1969; LEVINSONand BAR ILAN, 1970; LEVINSONand LEVINSON,1973; CROSS et al., 1976). Because it is not yet known whether sex attractant and aggregant responses are elicited by identical or different compounds, any relationship between the calling and aggregating behaviours of T. granarium females must still be elucidated. Light cycle control of the T. granarium calling pattern resembled that found for T. glabrum (HAMMACKand BURKHOLDER,1976) in that, regardless of daylength, a stable
Calling Behaviour in Female Trogodermu
granarium
‘9
phase relationship was maintained between daily calling maxima and photophase midpoints. However, the possibility that a circadian calling rhythm entrainable by photoperiod exists in T. granarium, as in T. glahrum (HAMMACK and BURKHOLDER, 1976). remains to be investigated. .4cktlowledgrnlr,lts-Research supported by the College of Agricultural and Life Sciences. University of Wisconsin, Madison: by a University of Wisconsin Travel Grant; and by a cooperative agreement between the University of Wisconsin and the Agricultural Research Service, USDA. The British Ministry of Agriculture. Fisheries and Food kindly permitted use of facilities at the Pest Infestation Control Laboratory. Slough. England. We particularly appreciate the assistance of Dr D. G. H. HALSTEAD, in whose laboratory the work was done. and of Dr R. W. HOWE in arranging the visit. Dr P. D. COX kindly supplied insect cultures. and Drs J. A. COFFELT and D. G. H. HALSTEAD contributed useful criticisms of the manuscript. REFERENCES AIXESAI‘;. C.. RAHALRAK. G. W. and TAMHANKAR, A. J. (1969) EfIect of age and previous mating on the response of khapra beetle males to female sex pheromone. Enrornologiu exp. uppl. 12. 229-234. BARAK. A. V. and BURXHOLDER. W. E. (1977) Behavior and pheromone studies with Arttrgrrrto ;,~ofl~~~r~~~t~s Casey (Coleoptera: Dermestidae). J. them. Ecol. 3, 219-237. BURKHOLIXR. W. E.. MA, M.. KUWAHARA, Y. and MATSUMURA. F. (1974) Sex pheromone of the furniture carpet beetle. Anrhrmus flariprs (Coleoptera: Dermestidae). Can Eur. 106, 835-839. CROSS. J. H.. B~LEK. R. C.. CASSIDY. R. F.. SILVERST~.IN,R. M.. GREENBLATT. R. E.. BURI(HOLI)ER. W. E.. LIVINSON. A. R. and LEVINSON, H. Z. (1976) Porapak-t) collection of pheromone components and isolation of (Z)- and (E)-l4-methyl-8-hexadecenal, sex pheromone components. from the females of four species of Troc/c~dww (Coleoptera: Dermestidae). J. chrm. Ecol. 2, 457468. FINGER(BAR-ILAN). A.. STANK. V. and SHULOV, A. (1965) Attracting substance (pheromone) produced by virgin females of Trogodcvwu granurium Everts (Cal. Dermestidae). Rir. Purussir. 26. 27-29. HAMMACR. L. and BURKHOLUEK, W. E. (1976) Circadian rhythm of sex pheromone-releasing behaviour in females of the dermestid beetle. Troyodrrniu ylahruui: regulation by photoperiod. J. /n.src,r Phr~iol. 22. 385-388. HAMMACK. L.. MA. M. and BURKHOLDER. W. E. (1976) Sex pheromone-releasing behaviour in females of the dermestid beetle. Trogodemu glahrum. J. ln.sect Physiol. 22. 555-561. KAKNAVAK.G. K. (1972) Mating behaviour and fecundity in Trogodermu yrumritott (Coleoplera: Dermestidnc). J. .\forcd Prod. Res. 8. 65-69. LEVINSON. H. Z. and BAR ILAN. A. R. (1970) Olfactory and tactile behaviour of the khapra beetle. Trogodermu grunurium. with special reference to its assembling scent, J. Insect Physiol. 16, 561-572. LE~INSON. H. Z. and LI:VINSON. A. R. 11973) The dual function of the assembling scent of the female khapra beetle Trogodrrwa grutwrirrm N,t,rwisse,tschaftm 60. 352-353. Snt:t_.R. G. D. and TORRIC.J. H. (1960) Prirtciples and Procedures oj’Srati.sric.s. McGraw-Hill. New York. VOELKEL. H. ( 1924) Zur Biologie und Bekampfung des Khaprakafers. Trogoderma granurium Everts. .4rh. hrol. EwtdAnv. Lutld-u. Forsrw. Berlin 13. 129-I 7 I.
and Household of Entomology,
and W. E. BURKHOLDER
Insects Laboratory. Agricultural Research. SEA, USDA. University of Wisconsin. Madison. WI 53706 U.S.A.
(First recrirrd
3 October
19801
Abstract--The effects of photoperiod. insemination, and age on the calling and mating activities of Trogodrrrna granurium females were investigated. Among mature virgin females held on 10: 14. 12: 12. or 16:8 LD. some calling behaviour was observed throughout photophase but 75”,, or more females were active for a period lasting about 8 hr/day. Under all three light regimes. this period was centred around the middle of photophase when virtually IOO”, of females assumed the calling posture. Correlated with diurnal fluctuations in female calling. mating frequency was higher towards the middle as compared to the start of photophase. In contrast to virgins. only increases in both about 3”,, of recently mated females engaged in calling activity. Significant calhng and female receptivity to mating occurred between the 1st and 3rd days of adult life. but the daily calling pattern of virgin females remained stable between the 4th and 10th days.
INTRODUCTION SEX PHEROMONE release by Trogoderma gkzhrum (Herbst) females is accompanied by characteristic postural activity which can be termed sex pheromone-releasing, or calling behaviour (HA~IMACK et al., 1976). The purposes of this study were to establish the existence of similar calling behaviour in the khapra beetle, Trogoderma granurium Everts. and to investigate the effects of age, insemination, and photoperiod on the calling and mating activities of T. yranarium females. MATERIALS
AND
METHODS
T. yranarium were obtained from stocks maintained at the Pest Infestation Control Laboratory, Slough, England. Larvae were reared on a 7:3 mixture by weight of whole wheat and wheat feed at 30°C and 70% r.h. in a 16 hr light: 8 hr dark (16:8 LD) photoperiod (3 a.m. L:7 p.m. D). Insects were removed from culture as pupae, sexed, and held in various numbers in 9 cm dia Petri dishes lined with filter papers. The dishes were examined at 1 day intervals and beetles having emerged from the pupal cuticle within that interval were ascribed an age of s-1 days. These insects pupate within the last larval cuticle and remain quiescent within the dorsally-split larval skin for up to several days after emergence from the pupal cuticle. Young adults, unless tested on the day of emergence, were removed from the larval cuticle at l-2 or 2-3 days of age. Adult males were held like pupae but in groups of .%lOO/dish. Females were maintained in lots of 25-30/dish, and provided with pleated filter paper strips as previously described (HAMMACK et al., 1976). All experiments were conducted in a test chamber that was maintained at 27.5 & 1°C and 60 + 29:, r.h. The photoperiod in this chamber was either 10: 14 (7 a.m. L:5 p.m. D), 12: 12 (7 a.m. L:7 p.m. D), or 16:8 LD (5 a.m. L:9 p.m. D) as specified below. Insects were transferred to the test chamber during the pupal stadium to ensure exposure to the experimental light regime for at least a 5-day period immediately preceding testing. Light intensity during photophase test periods was about 950 lx. Abdominal elevation, along with concomitant extension of at least the mesothoracic legs, was the criterion used to identify calling behaviour. Females whose calling activity *Present address: Metabolism ND 58105 U.S.A.
and Radiation
Research
Laboratory.
Agricultural
Research.
SEA. USDA.
Fargo.
L.
26
HAMMACK and
W. E. BURKHOLDER
was to be monitored were transferred from dishes to individual 5.0 x 1.5 cm glass shell vials usually 1 day before observation. Each vial was lined with a filter paper disk, and contained a strip of pleated filter paper (about 3.0 x 0.5 cm) to provide a vertical surface for calling activity. The number of females calling was recorded every f hr throughout one photophase interval in the test series described below. A series of three experiments was carried out as follows: (1) The eflect offemale age on calling was investigated on 10: 14 LD by observing the behaviour of 8 groups of 20 females ranging in age from c-1 to l&l 1 days. (2) The efSect of daylength on calling periodiciry was investigated by observing 60, 67 day females held on 10: 14 LD; 5-7 day females held on 12 : 12 LD; and 40, 4-6 day females held on 16 : 8 LD. (3) The effect of mating on culling was investigated on 10: 14 LD by observing 20, 45 day females that had been previously paired with 8-10 day-old males. Mixed-sex pairs had been left undisturbed in filter paper lined, 5.0 x 1.5 cm shell vials for a 19 hr period ending at lights-on time on the day of observation. Both paired and control groups were in this case transferred to observation vials f hr before the first calling records were taken. Vials from which mixed-sex pairs had been removed were retained and, on the day after calling activity was recorded, all vials were inspected for eggs to verify that previously paired females had oviposited. Only those females that oviposited were considered to have mated. (Comparable estimates of the percentage of females inseminated were obtained in preliminary tests in which copulatory success was scored both visually during pairing, and by observing the subsequent ovipositional behaviour of the previously paired females.) In addition, tests were conducted to investigate diurnal periodicity of mating activity and the effect of female age on receptivity to mating. To handle large samples conveniently, mating activity in both experiments was estimated by placing mixed-sex pairs in filter paper lined, 5.0 x 1.5 cm shell vials for 5 min, isolating the females in gelatin capsules (No. 000) containing crumpled black paper, and checking the capsules for eggs 48 hr or more after pairing. Only those pairs that subsequently produced ovipositing females were considered to have mated. In the diurnal periodicity experiment, the mating activity of 5-7 day females paired with 4-6 day males was compared between 1.5 hr intervals beginning 0 and 5.5 hr after the start of a 10 hr photophase. Seventy-five females were paired during each 1.5 hr interval. An equal number of unpaired virgin females of the same age were transferred to oviposition capsules as controls. In addition to scoring the later ovipositional behaviour of both groups, male copulatory attempts were noted during pairing of the treatment group. To investigate the efSect of female age on receptivity to mating, the number of females that oviposited after being paired at l-2, 2-3 or 34 days with 4-13 day-old males was determined. (Groups of 4-6, 9911 and 1l-13 day-old males were equally distributed among the three female age groups.) Five minute pairing periods were all confined to a 1.5 hr interval beginning 6 hr after the start of a 10 hr photophase. Each age group contained 38 females. A control group consisted of 38 virgin females, half 2-3 and half 34 days old when transferred to oviposition capsules. RESULTS
Description
of calling hehaviour
T. granarium females were observed to assume a stationary posture like that of T. glabrum in which the abdomen was elevated and the ovipositor at least partially exposed. A more detailed description of the T. glabrum calling posture was reported previously (HAMMACK et al., 1976). However, unlike groups of T. glabrum females which formed
inactive aggregates when not calling but which became motile and dispersed just prior to the onset of calling, groups of T. granarium females remained aggregated throughout the day. There was no period of locomotory activity preceding calling nor were occasional ovipositor probings like those described for T. glabrum evident. Calling behaviour was not conspicuous upon casual observation of T. granarium aggregates, and its frequency was difficult to determine accurately even upon careful examination. It was for this
Calling
Behaviour
in Female
Trogodermu
grtmurium
TABLE I. EFFECTOF AGE ON THE PHOTOPHASE CALLINGBEHAVIOUROF VIRGIN Trogoderma grmariun~ FEMALES (10: 14 LD)
No. of
Age (days)
females
&l I --2 2- 3 334 445 5 -6 89
20 20 20 20 20 20 20 20
I@-11
Percentage of females calling
Mean calling frequency per calling female ( k SE)*
0
5 80 100 100 100 100 lo0
2.0 Il.2 14.5 15.0 15.8 15.7 16.1
* Based on observations made at + hr intervals total of 21 observations/female.
reason that all tests were conducted easily monitored.
throughout
* 0.8 * 0.7 + 0.5 * 0.5 k 0.8 f0.3
photophase
providing
a
with isolated females whose activities were more
EfSect offemale age on calling and mating behaviours
Eighty per cent of 2-3 day old females were observed to call but little or no activity occurred in younger groups (Table 1). Judging from the number of individuals engaged in calling, however. and especially from the frequency of such behaviour, maximum levels were not reached until 34 days. Thereafter, the calling pattern remained stable until 10-11 days, the oldest age tested. The percentages of females which oviposited after pairing, and were thus considered to have been receptive to mating l-2,2-3 and 34 days after emergence, were 28.9, 86.8. and 76.3x, respectively. (Virgin controls laid no eggs.) Although there was no significant difference between 2-3 and 34 day groups, fewer l-2 day females mated as compared to the combined 2--3 and 3-4 day-old group [P < 0.001, partitioning the overall 1’ into independent comparisons (STEEL and TORRIE, 196011. Diurnal periodicity of calling and mating hehaviours
Photophase calling patterns displayed on 10:14, 12: 12 and 16:8 LD are shown in Fig. 1. Although calling occurred throughout the day, in each case activity was maximal toward the middle of photophase when virtually all females were in the calling position. Regardless of photoperiod, 75% or more females called for an interval lasting about
OLtckxp 0 5
--
0
Hours FIG. 1. Photophase calling patterns
12:12.
and
16:8
LD.
Light
16 8 LD
12 12LD
IO 14 LD
6
after
12
start
of
0I
6
16
photophase
of adult virgin Trogoderma granarium females held on 10: 14. portions of bars represent photophase: dark portions represent scotophase.
28
L.
HAMMACK
and
W. E. BURKHOLDER
8 hr/day, but a stable phase relationship was maintained between this interval and photophase midpoints. Thus, while exposure to longer daylengths had relatively little effect on the intensity or duration of daily calling periods, such manipulation did delay the onset of peak activity relative to lights-on time. The observation that some females were calling at lights-on and lights-off times suggests that some scotophase (dark phase) activity went unrecorded, especially on 10: 14 LD. Judged by ovipositional response, significantly more females mated when they were paired 5.5-7.0 hr (73.3%) as compared with O-l.5 hr (56.0x), after the onset of a 10 hr photophase (P < 0.05, computing the interaction x2 corrected for continuity for a 2 x 2 contingency table (STEEL and TORRIE, 1960)). (None of the virgin controls laid eggs.) There was, however, no significant difference between the two intervals when the percentage of males attempting copulation (90.7 and 94.7%) was considered. This suggests that the observed difference in mating activity was due primarily to diurnal changes in female receptivity to males. Eflect of mating on calling behaviour
Of the 30 females previously paired with males in an attempt to obtain mated individuals, none oviposited prior to the start of calling observations, but 29 had laid eggs between 19 and 48 hr after pairing. None of the virgin controls oviposited. Disregarding the one unfertile female whose mating status was uncertain, 3.4% (l/29) of mated females called during the photophase interval after copulation. This contrasted with 100% of the virgin controls. DISCUSSION Females of three dermestid beetle species including Anthrenusjavipes LeConte (BURKHOLDERet al., 1974), Trogoderma glabrum (HAMMACKet al., 1976), and Attagenus elongatulus Casey (BARAKand BURKHOLDER,1977) have been shown to assume a ‘headstand’ posture during sex pheromone release. Although bioassay tests were not conducted as in these studies, the results presented here are consistent with the assumption that similar postural activity by T. granarium females is indicative of pheromone release. Firstly, increases in both female calling and mating were most obvious between l-2 and 2-3 days after eclosion. Secondly, mating occurred more readily during midphotophase periods of peak calling activity than it did early in photophase before maximal daily calling levels had been established. Finally, insemination resulted in a significant reduction in calling during the photophase interval following copulation. Eventual recovery of calling would be predicted, however, as KARNAVAR(1972) reported that T. granarium females do not lay a full complement of eggs after one mating but remate soon after the first batch of eggs is oviposited. ‘VOELKEL(1924) was the first to suggest that T. granarium females produce a sex pheromone and the first to hypothesize that female behaviour could be used as an indicator of pheromone release. He observed that only virgin females perform grasping movements with their protruded ovipositors and postulated that this activity deposits on the substrate a chemical message serving to attract sexually receptive males. Even though females that we considered to be calling did partially protrude their ovipositors, there was little tendency to contact the substrate with this organ. The behaviour that we studied was thus distinct from that described by VOELKEL (1924). Nevertheless, his suggestion that T. granarium females produce a sex pheromone has been substantiated, although some investigators consider it to be an assembling scent that acts both as a male sex attractant and female aggregant (FINGER et al., 1965; ADEESANet al., 1969; LEVINSONand BAR ILAN, 1970; LEVINSONand LEVINSON,1973; CROSS et al., 1976). Because it is not yet known whether sex attractant and aggregant responses are elicited by identical or different compounds, any relationship between the calling and aggregating behaviours of T. granarium females must still be elucidated. Light cycle control of the T. granarium calling pattern resembled that found for T. glabrum (HAMMACKand BURKHOLDER,1976) in that, regardless of daylength, a stable
Calling Behaviour in Female Trogodermu
granarium
‘9
phase relationship was maintained between daily calling maxima and photophase midpoints. However, the possibility that a circadian calling rhythm entrainable by photoperiod exists in T. granarium, as in T. glahrum (HAMMACK and BURKHOLDER, 1976). remains to be investigated. .4cktlowledgrnlr,lts-Research supported by the College of Agricultural and Life Sciences. University of Wisconsin, Madison: by a University of Wisconsin Travel Grant; and by a cooperative agreement between the University of Wisconsin and the Agricultural Research Service, USDA. The British Ministry of Agriculture. Fisheries and Food kindly permitted use of facilities at the Pest Infestation Control Laboratory. Slough. England. We particularly appreciate the assistance of Dr D. G. H. HALSTEAD, in whose laboratory the work was done. and of Dr R. W. HOWE in arranging the visit. Dr P. D. COX kindly supplied insect cultures. and Drs J. A. COFFELT and D. G. H. HALSTEAD contributed useful criticisms of the manuscript. REFERENCES AIXESAI‘;. C.. RAHALRAK. G. W. and TAMHANKAR, A. J. (1969) EfIect of age and previous mating on the response of khapra beetle males to female sex pheromone. Enrornologiu exp. uppl. 12. 229-234. BARAK. A. V. and BURXHOLDER. W. E. (1977) Behavior and pheromone studies with Arttrgrrrto ;,~ofl~~~r~~~t~s Casey (Coleoptera: Dermestidae). J. them. Ecol. 3, 219-237. BURKHOLIXR. W. E.. MA, M.. KUWAHARA, Y. and MATSUMURA. F. (1974) Sex pheromone of the furniture carpet beetle. Anrhrmus flariprs (Coleoptera: Dermestidae). Can Eur. 106, 835-839. CROSS. J. H.. B~LEK. R. C.. CASSIDY. R. F.. SILVERST~.IN,R. M.. GREENBLATT. R. E.. BURI(HOLI)ER. W. E.. LIVINSON. A. R. and LEVINSON, H. Z. (1976) Porapak-t) collection of pheromone components and isolation of (Z)- and (E)-l4-methyl-8-hexadecenal, sex pheromone components. from the females of four species of Troc/c~dww (Coleoptera: Dermestidae). J. chrm. Ecol. 2, 457468. FINGER(BAR-ILAN). A.. STANK. V. and SHULOV, A. (1965) Attracting substance (pheromone) produced by virgin females of Trogodcvwu granurium Everts (Cal. Dermestidae). Rir. Purussir. 26. 27-29. HAMMACR. L. and BURKHOLUEK, W. E. (1976) Circadian rhythm of sex pheromone-releasing behaviour in females of the dermestid beetle. Troyodrrniu ylahruui: regulation by photoperiod. J. /n.src,r Phr~iol. 22. 385-388. HAMMACK. L.. MA. M. and BURKHOLDER. W. E. (1976) Sex pheromone-releasing behaviour in females of the dermestid beetle. Trogodemu glahrum. J. ln.sect Physiol. 22. 555-561. KAKNAVAK.G. K. (1972) Mating behaviour and fecundity in Trogodermu yrumritott (Coleoplera: Dermestidnc). J. .\forcd Prod. Res. 8. 65-69. LEVINSON. H. Z. and BAR ILAN. A. R. (1970) Olfactory and tactile behaviour of the khapra beetle. Trogodermu grunurium. with special reference to its assembling scent, J. Insect Physiol. 16, 561-572. LE~INSON. H. Z. and LI:VINSON. A. R. 11973) The dual function of the assembling scent of the female khapra beetle Trogodrrwa grutwrirrm N,t,rwisse,tschaftm 60. 352-353. Snt:t_.R. G. D. and TORRIC.J. H. (1960) Prirtciples and Procedures oj’Srati.sric.s. McGraw-Hill. New York. VOELKEL. H. ( 1924) Zur Biologie und Bekampfung des Khaprakafers. Trogoderma granurium Everts. .4rh. hrol. EwtdAnv. Lutld-u. Forsrw. Berlin 13. 129-I 7 I.