Journal of Chemical Ecology, VoL 7, No. 1, 1981
SCENT TRAILING BY VIRGIN F E M A L E S OF P s e u d o c o c c u s calceolariae ~,2
G. ROTUNDO a n d E. TREMBLAY lstituto di Entomologia Agraria dell' Universitb di Napoli 80055 PorticL Italy
(Received November 21, 1979;revised March 3, 1980) Abstract--Virgin females of the citrophilous mealybug Pseudococcus calceolariae (Mask.) deposit scent marks as trails on the substrate on which they rest or move. These substances elicit attraction and sexual behavior by conspecific males. The same responses were obtained when males were bioassayed on extracts from flter paper disks on which females had rested. The significanceof scent trailing in mealybugs is discussed.
Key Words--Scent marking, scent trailing, mealybugs, sex pheromone(s), citrus, Pseudococcus calceolariae, Homoptera, Pseudococcidae. INTRODUCTION Scent trailing has never been observed in H o m o p t e r a . Scent m a r k i n g of filter paper a n d of a b d o m i n a l silky fluffs by virgin females was observed in the red pine scale M a t s u c o c c u s resinosae Bean et God. ( D o a n e , 1966). In this case, however, there was n o evidence that virgin females left scent trails while moving. D u r i n g o u r studies on s h o r t - r a n g e sex b e h a v i o r of the citrophilous m e a l y b u g P s e u d o c o c c u s calceolariae (Mask.) we noticed that males att e m p t e d c o p u l a t i o n on the places where virgin females had been located. This behavior was e x a m i n e d more closely d u r i n g the present research. METHODS AND MATERIALS A strain of P s e u d o c o c c u s calceolariae was reared in glass jars (18 • 17 I D cm) o n p o t a t o sprouts u n d e r controlled e n v i r o n m e n t a l c o n d i t i o n s I Homoptera, Coccoidea, Pseudococcidae. 2This work was supported by the Italian National Research Council (CNR). 85 0098-0331/ 81/0100-0085503.00/0 9 1981PlenumPublishingCorporation
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ROTUNDO AND TREMBLAY
(26 + 1~ C and 60 + 5% relative humidity). The jars were kept closed with a nylon screen (mesh opening 250 ~zm). New potatoes were synchronously colonized by crawlers by placing them on the screen of the jars which contained the mixed population (Rotundo, 1978). Virgin females were isolated by mechanically removing young male stages (cocoons). A first group of bioassays was carried out in closed Petri dishes (ID 100 mm) containing two small citrus leaves. On one of them, a virgin female had rested for 1 min in a registered position. The other leaf, on which no females had rested, was left as a check. At least 3 unmated males were placed on each leaf. Males which exhibited courtship behavior within 5 rain plus copulatory attempts were registered as positive responses. Each bioassay was replicated at least 5 times. All tests were carried out under fluorescent light (700 lux) at 26 + 1~ C temperature and 63 + 5% relative humidity. A second group of bioassays was carried out in empty Petri dishes in which females were left free to move. The displacements of each female were traced on the external glass surface by means of a soft pen. Males which were
FIG. 1. Scent marking in Pseudococcus calceolariae: (a) virgin female while marking on a citrus leaf; (b) conspecific males exhibiting courtship behavior on the place where the female was located.
SCENT MARKING BY MEALYBUGS
87
FIG. 2. Scent trailing in Pseudococcus calceolariae. Males in movement along the trail produced by a virgin female on glass; (arrow) copulatory attempts between males on the place from which the female had started.
able to follow the trails while exhibiting copulatory behavior were registered as positive responses. Replications and environmental conditions were as stated above. A third group of bioassays allowed females to rest on filter paper disks (2 cm in diameter) for 3 hr under small glass capsules. After removal of the females, the disks were placed in 2 ml ethyl ether for 1 hr at r o o m temperature. The extract was concentrated to 0.1 ml by means of nitrogen jets. The concentrate was bioassayed in microdosages of 30 #1 according to a previous
88
ROTUNDO AND TREMBLAY
technique (Rotundo and Tremblay, 1974). Male behavior was followed in all cases under low stereoscopic magnification (16• RESULTS AND D I S C U S S I O N
Observations confirmed that the leaf and glass surfaces on which virgin females had rested or moved became very attractive to conspecific males (Figures 1 and 2). On contact with the marked surfaces males exhibited typical sexual behavior consisting in rapid sweeping abdominal movements and copulatory attempts. Similar results were obtained from concentrated extracts. Of special interest is the capability of males to follow the female trail along several centimeters. From the vigorous copulatory attempts between searching males even on glass (Figure 2, arrow), it may be inferred that a rather high concentration of scent is deposited by females. This sequence has not been observed by us in the related species Pseudococcus obscurus (Essig) (obscure mealybug) nor in Planococcus citri (Risso) (citrus mealybug). Females of Pseudococcus calceolariae were never observed to extrude body structures except for the ventral adhesive circle (circulus), which is typical for pseudococcids. However, this structure seems not to be involved in the scent trailing by females. As a matter of fact, the circulus is extruded on the substrate only on occasion of upside-down resting phases. Instead, males behave as though they were in the presence of a continuous trail. Moreover, females of the two other mealybug species (the obscure and citrus mealybugs), in spite of having a regular circulus, do not deposit scent trails. The sexual behavior of males suggests that the females utilize the sex pheromone(s) for scent trailing. We cannot exclude the possibility, however, that some other substance(s) may be involved. It seems clear that scent deposition ensures the continuity of the pheromone plume among wax masses, crevices, and fruits. REFERENCES DOANE, C.C. 1966. Evidence for a sex attractant in females of the red pine scale. J. Econ. Entornol. 59:1539-1540. ROTUNDO, G. 1978. Isolamento massale di femmine vergini d! Pseudococcus calceolariae (Mask.) mediante l'uso di un ormone giovanile. Boll. Lab. Entomol. Agr. "F. Silvestri'" Portici 35:162-168. ROTUNDO, G., and TREMBLAY, E. 1974. Studi su un feromone sessuale del Planococcus cirri (Risso), lI. Estrazione. Boll. Lab. EntomoL Agr. "F. Silvestri" Portici 31:121-131.
SCENT TRAILING BY VIRGIN F E M A L E S OF P s e u d o c o c c u s calceolariae ~,2
G. ROTUNDO a n d E. TREMBLAY lstituto di Entomologia Agraria dell' Universitb di Napoli 80055 PorticL Italy
(Received November 21, 1979;revised March 3, 1980) Abstract--Virgin females of the citrophilous mealybug Pseudococcus calceolariae (Mask.) deposit scent marks as trails on the substrate on which they rest or move. These substances elicit attraction and sexual behavior by conspecific males. The same responses were obtained when males were bioassayed on extracts from flter paper disks on which females had rested. The significanceof scent trailing in mealybugs is discussed.
Key Words--Scent marking, scent trailing, mealybugs, sex pheromone(s), citrus, Pseudococcus calceolariae, Homoptera, Pseudococcidae. INTRODUCTION Scent trailing has never been observed in H o m o p t e r a . Scent m a r k i n g of filter paper a n d of a b d o m i n a l silky fluffs by virgin females was observed in the red pine scale M a t s u c o c c u s resinosae Bean et God. ( D o a n e , 1966). In this case, however, there was n o evidence that virgin females left scent trails while moving. D u r i n g o u r studies on s h o r t - r a n g e sex b e h a v i o r of the citrophilous m e a l y b u g P s e u d o c o c c u s calceolariae (Mask.) we noticed that males att e m p t e d c o p u l a t i o n on the places where virgin females had been located. This behavior was e x a m i n e d more closely d u r i n g the present research. METHODS AND MATERIALS A strain of P s e u d o c o c c u s calceolariae was reared in glass jars (18 • 17 I D cm) o n p o t a t o sprouts u n d e r controlled e n v i r o n m e n t a l c o n d i t i o n s I Homoptera, Coccoidea, Pseudococcidae. 2This work was supported by the Italian National Research Council (CNR). 85 0098-0331/ 81/0100-0085503.00/0 9 1981PlenumPublishingCorporation
86
ROTUNDO AND TREMBLAY
(26 + 1~ C and 60 + 5% relative humidity). The jars were kept closed with a nylon screen (mesh opening 250 ~zm). New potatoes were synchronously colonized by crawlers by placing them on the screen of the jars which contained the mixed population (Rotundo, 1978). Virgin females were isolated by mechanically removing young male stages (cocoons). A first group of bioassays was carried out in closed Petri dishes (ID 100 mm) containing two small citrus leaves. On one of them, a virgin female had rested for 1 min in a registered position. The other leaf, on which no females had rested, was left as a check. At least 3 unmated males were placed on each leaf. Males which exhibited courtship behavior within 5 rain plus copulatory attempts were registered as positive responses. Each bioassay was replicated at least 5 times. All tests were carried out under fluorescent light (700 lux) at 26 + 1~ C temperature and 63 + 5% relative humidity. A second group of bioassays was carried out in empty Petri dishes in which females were left free to move. The displacements of each female were traced on the external glass surface by means of a soft pen. Males which were
FIG. 1. Scent marking in Pseudococcus calceolariae: (a) virgin female while marking on a citrus leaf; (b) conspecific males exhibiting courtship behavior on the place where the female was located.
SCENT MARKING BY MEALYBUGS
87
FIG. 2. Scent trailing in Pseudococcus calceolariae. Males in movement along the trail produced by a virgin female on glass; (arrow) copulatory attempts between males on the place from which the female had started.
able to follow the trails while exhibiting copulatory behavior were registered as positive responses. Replications and environmental conditions were as stated above. A third group of bioassays allowed females to rest on filter paper disks (2 cm in diameter) for 3 hr under small glass capsules. After removal of the females, the disks were placed in 2 ml ethyl ether for 1 hr at r o o m temperature. The extract was concentrated to 0.1 ml by means of nitrogen jets. The concentrate was bioassayed in microdosages of 30 #1 according to a previous
88
ROTUNDO AND TREMBLAY
technique (Rotundo and Tremblay, 1974). Male behavior was followed in all cases under low stereoscopic magnification (16• RESULTS AND D I S C U S S I O N
Observations confirmed that the leaf and glass surfaces on which virgin females had rested or moved became very attractive to conspecific males (Figures 1 and 2). On contact with the marked surfaces males exhibited typical sexual behavior consisting in rapid sweeping abdominal movements and copulatory attempts. Similar results were obtained from concentrated extracts. Of special interest is the capability of males to follow the female trail along several centimeters. From the vigorous copulatory attempts between searching males even on glass (Figure 2, arrow), it may be inferred that a rather high concentration of scent is deposited by females. This sequence has not been observed by us in the related species Pseudococcus obscurus (Essig) (obscure mealybug) nor in Planococcus citri (Risso) (citrus mealybug). Females of Pseudococcus calceolariae were never observed to extrude body structures except for the ventral adhesive circle (circulus), which is typical for pseudococcids. However, this structure seems not to be involved in the scent trailing by females. As a matter of fact, the circulus is extruded on the substrate only on occasion of upside-down resting phases. Instead, males behave as though they were in the presence of a continuous trail. Moreover, females of the two other mealybug species (the obscure and citrus mealybugs), in spite of having a regular circulus, do not deposit scent trails. The sexual behavior of males suggests that the females utilize the sex pheromone(s) for scent trailing. We cannot exclude the possibility, however, that some other substance(s) may be involved. It seems clear that scent deposition ensures the continuity of the pheromone plume among wax masses, crevices, and fruits. REFERENCES DOANE, C.C. 1966. Evidence for a sex attractant in females of the red pine scale. J. Econ. Entornol. 59:1539-1540. ROTUNDO, G. 1978. Isolamento massale di femmine vergini d! Pseudococcus calceolariae (Mask.) mediante l'uso di un ormone giovanile. Boll. Lab. Entomol. Agr. "F. Silvestri'" Portici 35:162-168. ROTUNDO, G., and TREMBLAY, E. 1974. Studi su un feromone sessuale del Planococcus cirri (Risso), lI. Estrazione. Boll. Lab. EntomoL Agr. "F. Silvestri" Portici 31:121-131.
