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Morphology and development rates of males and females of Xyleborus ferrugineus (Fabr.) (Coleoptera : Scolytidae) during metamorphosis
Int. Y. Insect Morpk,ol. & Embryol. 6(1): 31-39. 1977. Pergamon Press. Printed in Great Britain.
MORPHOLOGY A N D DEVELOPMENT RATES OF MALES A N D FEMALES OF XYLEBORUS FERRUGINEUS (FABR.) (COLEOPTERA • SCOLYTIDAE) D U R I N G METAMORPHOSIS JOEL G. KINGSOLVERand DALE M. NORRIS Department of Entomology, University of Wisconsin, Madison, Wisconsin 53706, U.S.A. (Accepted 1 November 1976)
Abstract--The developmental rate and external morphology of males and females of the ambrosia beetle, Xyleborusferrugineus, during metamorphosis were studied by light and scanning electron microscopy. Special emphasis was placed on the development of sexually dimorphic features. There was no difference in the developmental rate of male and fi~male larvae or pupae. Pupation occurred 8.1 ± 1.2 days after eclosion, and the pupal stage lasted 4.6 i 0.6 days. A generalized sequence of the daily developmental event:~ prior to and during metamorphosis is given. The development of the very distinctive pronotal horn and degenerate metathoracic wing of the male during metamorphosis is discussed. The setal pattern of the pronotum and the posterior processes on the pro- and mesothoracic coxae of the pupae are unique to the pupal stage. The information on X. ferrugineus provided in this paper, plus that given in our cited previous publications on this unique insect, establish a foundation of knowledge which should make the animal highly useful in certain experimental analyses of developmental biology. Index descriptors (in addition to those in title): Larva, prepupa, pupa, ecdysis, haploids, diplo[ds, holometabolous.
INTRODUCTION AN IMPORTANT component of successful research programs in current developmental biology and genetics is choice of organism. The ambrosia beetle, X. ferrugineus, has numerous attributes which make it particularly useful for certain developmental and genetic studies. Our research has sought to identify and characterize some of these traits. Several of its more important characteristics are: haploid-diploid sex determination; arrhenotokous parthenogenetic reproduction (Norris and Chu, 1970); unusual sterol requirements for pupation (Chu et al., 1970); and ease of continuous laboratory rearing with, and without, microbial symbiotes (Norris, 1972). A previous paper (Kingsolver and Norris, 1977), one in a series on the external morphology and/or developmental rates for the life stages of this insect (Peleg and Norris, 1973; Chu et al., 1975; Chu and Norris, 1976; Beeman and Norris, 1977a, b), partially characterized the marked sexual dimorphism in the adult X. fer,,ugineus. Major morphological differences studied in the adult males and females involved: (1) overall body size; (2) length/width ratio of the pronotum and elytron; (3) the male pronotal horn; (4) setal patterns; and (5) the metathoracic wing. In the present study a timed sequence of the developmental rates of certain external morphological features is given. The comparative morphogenesis of sexually dimorphic features in the prepupa and pupa is especially emphasized. 31
32
JOELG. KINGSOLVERand DALEM. NORRIS
MATERIALS AND METHODS In Xiferrugineus, females are produced from fertilized eggs, and males from unfertilized eggs. Mated females generally produce at least 20 female progeny for each male. There are no apparent external morphological differences between males from mated and unmated females. Twenty-one offspring from mated females and 18 offspring from unmated females, reared on oligidic diet in the presence of symbiotic microbes in test tubes (Norris, 1972), were observed daily, beginning with eclosion. From day 5 after eclosion until adult emergence, each insect was photographed daily through a dissecting microscope at x 25. Males are identifiable as mature larvae, and such larvae, produced by mated females, were excluded from the final analyses. A second group of X.ferrugineus was similarly reared and observed daily beginning with eclosion. Insects representing each mean daily developmental stage (as determined above with light microscopy) from day 5 after eclosion to adult emergence were fixed, critical-point dried, and mounted for viewing with scanning electron microscopy (SEM). Forty-three females and 25 males were examined with SEM. RESULTS
Timed sequence of developmental events during metamorphosis Because the time between eclosion and pupation varies, depending especially upon the feeding and nutritional state of the larva, studied developmental events were defined in relation to the day of pupation (day 0). There were no observed significant differences between males and females in the rates of external morphological development during metamorphosis. In artificial diet (Norris, 1972) with symbiotic microbes, pupation occurred 8.1 ~ 1.2 days after eclosion, and the pupal stage lasted 4.6 ± 0.6 days. The observed generalized sequence of the daily developmental events preceding and during metamorphosis was as follows : Day --3. There was a gradual thickening of the 3 thoracic segments of the larva. This was particularly evident in the dorsum (Fig. 1). Under the experimental conditions, this stage was seen during the third and final larval stadium about 5-6 days after eclosion. Male and female larvae were of similar length during early development. However, by day --3, when anterior thickening begins, the female larva was ca. 25 ~ longer than the male. Day --2. The thickening initiated in day 3 increased, particularly in the prothoracic segment, and made the anterior end of the larva "humpbacked". The head became flattened antero-posteriorly and may be tilted posteriorly and ventrally (Figs. 2, 3). Day --1. The thoracic segments were now thickened both dorsally and ventrally (Figs. 3, 4). The outlines of the developing pronotum and elytron may be visible. The larval head began to split dorsally and anteriorly, and peeled off ventrally (Fig. 4). Day O. Many pupal features were already well defined by day 0. A day 0 female pupa which is still covered by remnants of the larval cuticle, most notably the larval head and mouthparts, is shown in Fig. 5. Day 1. There were no significant observable differences between day 0 and day 1 pupae. A day 1 male pupa is shown in Fig. 6. A series of ventral views of a female day 1 pupa are seen in Figs. 7-10. The pupal cuticle was covered with a large number of very small, spine-shaped protuberances (Fig. 7). The femora were oriented approximately parallel to, and the tibiae approximately perpendicular to, the body axis. The metathoracic legs were partially hidden by the striated elytra and the wings which wrapped ventrally around the posterior of the pupa. The metathoracic coxae were small, and each had a pair of dome-shaped processes near the ventral midline. The mesothoracic coxae (Fig. 9) were larger and irregular in shape. Each had a dome-shaped process located ventro-posteriorly near the ventral midline, and a longer posteriorlypointing process located postero-distally. The prothoracic coxae (Fig. 9) were much larger,
Metamorphosis of
Xyleborus
PLATE 1 F~G. 1. Dorsal view of a female day --3 larva. H, head; T h prothorax. Scale -- 100 ~.m. FIG. 2. Lateral view of a "humpbacked" male day --2 larva. Scale -- 100/~m. FIG. 3. Ventral view of the anterior end of a female day --2 larva. Scale 100 ~m. FIG. 4. Ventral view of the head and thoracic segments (T1, T2, Ta) of a female day --1 larva. The developing clytron (E) and metathoracic wing (W) are visible. L, labium; LR, labrum; M, maxilla, MD, mandible. Scale -- 100 ~.m.
IMAE 6 / 1 - - C
33
34
JOEL G. KINGSOLVER a n d DALE M. NORRIS
PLATE 2 FIG. 5. Ventral view o f head o f a female day 0 p u p a . Both pupal m o u t h p a r t s (above) a n d larval m o u t h p a r t s (below) are visible. Scale ~ 50 ~m. FIG. 6. Ventral view o f a male d a y 0 p u p a . A, a n t e n n a ; H C , metathoracic coxa; H L , m e t a t h o r a c i c leg; M C , m e s o t h o r a c i c coxa; M L , m e s o t h o r a c i c leg; PC, prothoracic coxa; PL, prothoracic leg. Scale = 100 tzm. FIo. 7. Spine-shaped p r o t r u s i o n s o n surface o f p u p a l cuticle on prothoracic coxa. Scale -- 5/~m. FIG. 8. Ventral view o f a female day 1 pupa. Scale = 100 t~m.
Metamorphosis of Xyleborus
35
and oval in shape. Each had a pair of posteriorly-pointing processes; a short one located ventro-posteriorly near the ventral midline, and a long one located postero-distally. The pro- and mes~thoracic trochanters were attached to their respective coxae just dorsolaterally to the longer postero-distal process. A ventral view of the head and pronotum of a day 1 pupa is shown in Fig. 10. The antennae were straight and parallel to the body axis, and the terminal club was distinguishable from the remainder of the antenna. The labrum, mandibles, maxillae, and labium were identifiable. The maxillary and labial palpi were recognizable as ventrally-pointing dome-shaped processes; the labial palpi were nearly hidden below the stipes of the maxillae. There was a p~dr of setae just anterior to the labrum. There were a number of setae on the dorsal and lateral pronotum of the day 0 and day 1 pupa. Because. the dorsal pronotum of the day 0 pupa, particularly of the female, often collapses, the .setae were more easily viewed on older pupae (Figs. 13, 20). There were: (1) a row of 3 laterally-located setae, and 1 more medially-located seta, toward the posterior margin on each side of the pronotum; (2) 2 setae, 1 medially- and 1 laterally-located, toward the anterior margin on each side of the pronotum; and (3) 2 setae, 1 medially- and 1 laterally-located, midway between the anterior and posterior margins on each side of the pronotum. The metathoracic wing of the day 1 female was about as long as the elytron, and when the wing and elytron were folded ventrally around the pupa at the posterior end, the wing tip extended beyond that of the elytron (Fig. 8). The wing of the day 1 male was only approximatel:y one-half the size of the elytron, and did not extend beyond it when folded ventrally (Fig. 6). The metathoracic wing of a day 3 female pupa and a day 2 male pupa is shown in Figs. 17 and 18, respectively. The anterior pronotal horn of the male was not visible (Fig. 19). Day 2. The eyes and mandibles of the pupa were beginning to darken. The coxae, particularly the mesothoracic coxae, were larger and more clearly defined, and the posterior processes on the coxae had lengthened (Fig. 11). The anterior pronotal horn of the male first became visible (Fig. 20). Day 3. The eyes, mandibles, and maxillae stipes were dark, and the tibiae had begun to darken. The pupal cuticle became transparent, and the imago was visible beneath (Figs. 12, 13). The long processes on the prothoracic and mesothoracic coxae disappeared (Fig. 14). The anterior pronotal horn of the male was clearly demarcated (Fig. 15). Day 4. The imago emerged from the pupal cuticle (Fig. 15). Tanning and sclerotization continued and were completed within 1 day. The partially sclerotized elytron of an emerging male is shown in Fig. 16.
DISCUSSION Another recent study in our laboratory (Beeman and Norris, 1977a, b) showed that the developmental time to eclosion for male embryos was significantly (p < 0.05) longer than for female embryos (mean time from pole cell exclusion to eclosion was 106.5 vs. 103. 2 hr, respectively). Peleg and Norris (1973) reported that there was no significant difference in developmental time of male and female larvae through the 3 larval instars. Our results support this prior conclusion regarding larvae, and also indicate no difference in the developmental times of male and female pupae. Thus, for the period from eclosion through adult emerger~ce, there was no significant difference in overall developmental rate between
36
JOEL G. KINGSOLVERand DALE M. NORRIS
PLATE 3 FIG. 9. Ventral view of anterior thorax of a female day 1 pupa. Scale 50 t~m. F~G. 10. Head and prothorax of a female day 1 pupa. Scale -- 100 t~m. FIG. ll. Ventral view of anterior thorax of a female day 2 pupa. Scale 100 p.m. FIG. 12. Ventral view of anterior thorax of a female day 3 pupa. Imago is visible through pupal cuticle S c a l e - 100 t~m. males a n d females, a n d the q u a n t i t y o f genetic material in the h a p l o i d male thus was n o t a limiting factor in the overall d e v e l o p m e n t a l rates o f larva, p u p a , or adult. Peleg a n d N o r r i s 0 9 7 3 ) also r e p o r t e d t h a t male larvae c o u l d be reliably distinguished f r o m female larvae only in m a t u r e third instars. Such d e t e r m i n a t i o n s were m a d e on the basis o f h e a d - c a p s u l e width. O u r o b s e r v a t i o n s on d a y - - 3 (i.e., third instar) larvae also i n d i c a t e d that the female is a p p r o x i m a t e l y 25 ~ longer t h a n the male. Thus, by d a y - - 3 the sexual d i m o r p h i s m in overall b o d y size is a l r e a d y a p p a r e n t . H o w e v e r , the d a y - - 3 larva o f each sex is 20-30 ~ smaller t h a n the p u p a or adult.
Metamorphosis of Xyleborus
37
PLATE 4 Fit. 13. 12,orso-lateral view of pronotum of a female day 3 pupa. Adult setae (AS) are visible through pupal cuticle. PS, pupal setae. Scale = 100 #m. FIG. 14. Ventral view of pro- and mesothoracic coxae of a female day 3 pupa. Scale = 50 /~m. FIG. 15. Dorsal view of pronotum of a male day 4 pupa. Pupal cuticle has broken off on left side of adult pronotal horn (PH) and along posterior margin of pronotum. Scale = 100 p.m. FfG. 16. Dorsal view of partially sclerotized elytron of an emerging male. Scale = 100 /~m. Other m a j o r sexually d i m o r p h i c features in the p u p a include the metathoracic wing a n d p r o n o t u m . By day 0, the difference in size of the metathoracic wing between male a n d female was readily a p p a r e n t (Figs. 6, 8). A c o r r e s p o n d i n g size difference was also f o u n d in the wings of adults. The male adult, with its short degenerate wing (Fig. 18), is u n a b l e to
38
JOEL G. KINGS:)LVERand DALE M. NORRIS
PLATE 5
FIG. 17. Right elytron and metathoracic wing of a female day 3 pupa. The wing is about same length as elytron. Scale 100 ~m. FIG. 18. Right metathoracic wing of a male day 2 pupa. Wing extends only about halfway to posterior abdomen. Scale lO0 ~m. FIG. 19. Ventral view of anterior margin of pronotum (PN) and head of a male day 1 pupa. Pronotal horn is not visible. Scale -- 100 ~m. FIG. 20. Dorsal view of pronotum of a male day 2 pupa. Pronotal horn is just visible. Scale 100 t~m. fly; whereas, the female is a strong flier. The p r o n o t a l h o r n of the male, a p r o m i n e n t structure in this adult, was n o t visible on day 0 or day 1 (Fig. 19). It usually became visible by day 2 (Fig. 20), a n d was clearly evident by day 3 (Fig. 15). M e a s u r e m e n t s on the a n t e n n a , each thoracic leg, p r o n o t u m , a n d elytron indicated that these body parts are not significantly different (p < 0.05) in size in the day 1 p u p a a n d the adult. D a t a were b a s e d on 22 female a n d 17 male pupae, and 23 female a n d 22 male adults.
Metamarphosis of Xyleborus
39
The m e s o t h o r a c i c coxa in the d a y 1 p u p a is smaller (ca. 30-35 ~o) t h a n in the adult, but it is o f comparable, size by d a y 2 or 3. Because o f differences in form, c o m p a r i s o n s o f m o u t h parts were not m a d e . M o s t external p u p a l features are evident by d a y 0, a n d except for t a n n i n g a n d sclerotization, there is little further change until d a y 3. A n o t a b l e a n d interesting exception is the continuing d e v e l o p m e n t o f the male p r o n o t a l horn, because it becomes a m a j o r m o r p h o logical difference between male a n d female adults. A n o t h e r external p u p a l feature which u n d e r g o e s significant d e v e l o p m e n t d u r i n g the early p u p a l stage is the f o r m a n d lengthening o f the processes on the p r o - a n d m e s o t h o r a c i c coxae. These processes g r a d u a l l y disintegrate in the d a y 3 p u p a , a n d there is n o c o r r e s p o n d i n g structure in the a d u l t beetle. The setae on the d o r s a l a n d lateral p r o n o t u m , and a n t e r i o r to the l a b r u m also a p p e a r to be u n i q u e to the p u p a l stage. The setal p a t t e r n on the i m a g o is entirely different from that on the p u p a (Fig. 13). The i n f o r m a t i o n a b o u t X. ferrugineus d e v e l o p m e n t a n d m o r p h o l o g y p r o v i d e d in this paper, plus that previously p u b l i s h e d as cited, establishes the f o u n d a t i o n k n o w l e d g e necessary to use o f this unique a n i m a l system in m a n y types o f refined e x p e r i m e n t a l studies in d e v e l o p m e n t a l biology. Its usefulness in such future research m a y become second a m o n g insects only to Drosophila. Acknowledgemer, t--This research was supported by the Director of the Research Division, C.A.L.S., University of Wisconsin, Madison; and in part by research grant No. RR-00779 from the Division of Research Resources, National Institutes of Health, and by funds from the Schoenleber Foundation, Milwaukee, WI.
REFERENCES BEEMAN, S. L. alad D. M. NORRIS. 1977a. Embryogenesis of Xyleborusferrugineus. I. External morphology of male: and female embryo. J. Morphol. (in press). BEEMAN,S. L. and D. M. NORRIS. 1977b. Embryogenesis of Xyleborusferrugineus. II. Developmental rates of male and female embryos. J. Morphol. (in press). CHtJ, H. M. and D. M. NORRIS. 1976. Ultrastructure of the compound eye of the haploid male beetle Xylebo vusferrugineus. Cell Tissue Res. 168: 315-24. CHU, H. M., D. M. NORRISand S. D. CARLSON.1975. Ultrastructure of the compound eye of the diploid female beetle, Xyleborus ferrugineus. Cell Tissue Res. 165: 23-36. CHU, H. M., D. M. NORRISand L. T. KOK. 1970. Pupation requirement of the beetle, Xyleborusferrugineus: Sterols other than cholesterol. J. Inseet Physiol. 16: 1379-87. KINGSOLVER,J. G. and D. M. NORRIS. 1977. External morphology of Xyleborus ferrugineus. I. Head and protho tax of adult males. J. Morphol. (In press). NORRIS, D. M. 1972. Dependence of fertility and progeny development of Xyleborus ferrugineus upon chemicals from its symbiotes, pp. 299-310. In J. G. RODRIGUEZ(ed.) Insect and Mite Nutrition. North-Holland Co., Amsterdam. NORRIS, D. M. and H. M. CHtJ. 1970. Nutrition of Xyleborus ferrugineus. II. A holidic diet for the aposymbiotic insect. Ann. Entornol. Soe. Amer. 63:114245. PELE% B. and D. M. NORRIS. 1973. Haploid versus diploid Xyleborusferrugineus. I. Larval instars, development, and morphogenesis of the metathoracic wing. Ann. Entomol. Soc. Amer. 66: 180-83.
MORPHOLOGY A N D DEVELOPMENT RATES OF MALES A N D FEMALES OF XYLEBORUS FERRUGINEUS (FABR.) (COLEOPTERA • SCOLYTIDAE) D U R I N G METAMORPHOSIS JOEL G. KINGSOLVERand DALE M. NORRIS Department of Entomology, University of Wisconsin, Madison, Wisconsin 53706, U.S.A. (Accepted 1 November 1976)
Abstract--The developmental rate and external morphology of males and females of the ambrosia beetle, Xyleborusferrugineus, during metamorphosis were studied by light and scanning electron microscopy. Special emphasis was placed on the development of sexually dimorphic features. There was no difference in the developmental rate of male and fi~male larvae or pupae. Pupation occurred 8.1 ± 1.2 days after eclosion, and the pupal stage lasted 4.6 i 0.6 days. A generalized sequence of the daily developmental event:~ prior to and during metamorphosis is given. The development of the very distinctive pronotal horn and degenerate metathoracic wing of the male during metamorphosis is discussed. The setal pattern of the pronotum and the posterior processes on the pro- and mesothoracic coxae of the pupae are unique to the pupal stage. The information on X. ferrugineus provided in this paper, plus that given in our cited previous publications on this unique insect, establish a foundation of knowledge which should make the animal highly useful in certain experimental analyses of developmental biology. Index descriptors (in addition to those in title): Larva, prepupa, pupa, ecdysis, haploids, diplo[ds, holometabolous.
INTRODUCTION AN IMPORTANT component of successful research programs in current developmental biology and genetics is choice of organism. The ambrosia beetle, X. ferrugineus, has numerous attributes which make it particularly useful for certain developmental and genetic studies. Our research has sought to identify and characterize some of these traits. Several of its more important characteristics are: haploid-diploid sex determination; arrhenotokous parthenogenetic reproduction (Norris and Chu, 1970); unusual sterol requirements for pupation (Chu et al., 1970); and ease of continuous laboratory rearing with, and without, microbial symbiotes (Norris, 1972). A previous paper (Kingsolver and Norris, 1977), one in a series on the external morphology and/or developmental rates for the life stages of this insect (Peleg and Norris, 1973; Chu et al., 1975; Chu and Norris, 1976; Beeman and Norris, 1977a, b), partially characterized the marked sexual dimorphism in the adult X. fer,,ugineus. Major morphological differences studied in the adult males and females involved: (1) overall body size; (2) length/width ratio of the pronotum and elytron; (3) the male pronotal horn; (4) setal patterns; and (5) the metathoracic wing. In the present study a timed sequence of the developmental rates of certain external morphological features is given. The comparative morphogenesis of sexually dimorphic features in the prepupa and pupa is especially emphasized. 31
32
JOELG. KINGSOLVERand DALEM. NORRIS
MATERIALS AND METHODS In Xiferrugineus, females are produced from fertilized eggs, and males from unfertilized eggs. Mated females generally produce at least 20 female progeny for each male. There are no apparent external morphological differences between males from mated and unmated females. Twenty-one offspring from mated females and 18 offspring from unmated females, reared on oligidic diet in the presence of symbiotic microbes in test tubes (Norris, 1972), were observed daily, beginning with eclosion. From day 5 after eclosion until adult emergence, each insect was photographed daily through a dissecting microscope at x 25. Males are identifiable as mature larvae, and such larvae, produced by mated females, were excluded from the final analyses. A second group of X.ferrugineus was similarly reared and observed daily beginning with eclosion. Insects representing each mean daily developmental stage (as determined above with light microscopy) from day 5 after eclosion to adult emergence were fixed, critical-point dried, and mounted for viewing with scanning electron microscopy (SEM). Forty-three females and 25 males were examined with SEM. RESULTS
Timed sequence of developmental events during metamorphosis Because the time between eclosion and pupation varies, depending especially upon the feeding and nutritional state of the larva, studied developmental events were defined in relation to the day of pupation (day 0). There were no observed significant differences between males and females in the rates of external morphological development during metamorphosis. In artificial diet (Norris, 1972) with symbiotic microbes, pupation occurred 8.1 ~ 1.2 days after eclosion, and the pupal stage lasted 4.6 ± 0.6 days. The observed generalized sequence of the daily developmental events preceding and during metamorphosis was as follows : Day --3. There was a gradual thickening of the 3 thoracic segments of the larva. This was particularly evident in the dorsum (Fig. 1). Under the experimental conditions, this stage was seen during the third and final larval stadium about 5-6 days after eclosion. Male and female larvae were of similar length during early development. However, by day --3, when anterior thickening begins, the female larva was ca. 25 ~ longer than the male. Day --2. The thickening initiated in day 3 increased, particularly in the prothoracic segment, and made the anterior end of the larva "humpbacked". The head became flattened antero-posteriorly and may be tilted posteriorly and ventrally (Figs. 2, 3). Day --1. The thoracic segments were now thickened both dorsally and ventrally (Figs. 3, 4). The outlines of the developing pronotum and elytron may be visible. The larval head began to split dorsally and anteriorly, and peeled off ventrally (Fig. 4). Day O. Many pupal features were already well defined by day 0. A day 0 female pupa which is still covered by remnants of the larval cuticle, most notably the larval head and mouthparts, is shown in Fig. 5. Day 1. There were no significant observable differences between day 0 and day 1 pupae. A day 1 male pupa is shown in Fig. 6. A series of ventral views of a female day 1 pupa are seen in Figs. 7-10. The pupal cuticle was covered with a large number of very small, spine-shaped protuberances (Fig. 7). The femora were oriented approximately parallel to, and the tibiae approximately perpendicular to, the body axis. The metathoracic legs were partially hidden by the striated elytra and the wings which wrapped ventrally around the posterior of the pupa. The metathoracic coxae were small, and each had a pair of dome-shaped processes near the ventral midline. The mesothoracic coxae (Fig. 9) were larger and irregular in shape. Each had a dome-shaped process located ventro-posteriorly near the ventral midline, and a longer posteriorlypointing process located postero-distally. The prothoracic coxae (Fig. 9) were much larger,
Metamorphosis of
Xyleborus
PLATE 1 F~G. 1. Dorsal view of a female day --3 larva. H, head; T h prothorax. Scale -- 100 ~.m. FIG. 2. Lateral view of a "humpbacked" male day --2 larva. Scale -- 100/~m. FIG. 3. Ventral view of the anterior end of a female day --2 larva. Scale 100 ~m. FIG. 4. Ventral view of the head and thoracic segments (T1, T2, Ta) of a female day --1 larva. The developing clytron (E) and metathoracic wing (W) are visible. L, labium; LR, labrum; M, maxilla, MD, mandible. Scale -- 100 ~.m.
IMAE 6 / 1 - - C
33
34
JOEL G. KINGSOLVER a n d DALE M. NORRIS
PLATE 2 FIG. 5. Ventral view o f head o f a female day 0 p u p a . Both pupal m o u t h p a r t s (above) a n d larval m o u t h p a r t s (below) are visible. Scale ~ 50 ~m. FIG. 6. Ventral view o f a male d a y 0 p u p a . A, a n t e n n a ; H C , metathoracic coxa; H L , m e t a t h o r a c i c leg; M C , m e s o t h o r a c i c coxa; M L , m e s o t h o r a c i c leg; PC, prothoracic coxa; PL, prothoracic leg. Scale = 100 tzm. FIo. 7. Spine-shaped p r o t r u s i o n s o n surface o f p u p a l cuticle on prothoracic coxa. Scale -- 5/~m. FIG. 8. Ventral view o f a female day 1 pupa. Scale = 100 t~m.
Metamorphosis of Xyleborus
35
and oval in shape. Each had a pair of posteriorly-pointing processes; a short one located ventro-posteriorly near the ventral midline, and a long one located postero-distally. The pro- and mes~thoracic trochanters were attached to their respective coxae just dorsolaterally to the longer postero-distal process. A ventral view of the head and pronotum of a day 1 pupa is shown in Fig. 10. The antennae were straight and parallel to the body axis, and the terminal club was distinguishable from the remainder of the antenna. The labrum, mandibles, maxillae, and labium were identifiable. The maxillary and labial palpi were recognizable as ventrally-pointing dome-shaped processes; the labial palpi were nearly hidden below the stipes of the maxillae. There was a p~dr of setae just anterior to the labrum. There were a number of setae on the dorsal and lateral pronotum of the day 0 and day 1 pupa. Because. the dorsal pronotum of the day 0 pupa, particularly of the female, often collapses, the .setae were more easily viewed on older pupae (Figs. 13, 20). There were: (1) a row of 3 laterally-located setae, and 1 more medially-located seta, toward the posterior margin on each side of the pronotum; (2) 2 setae, 1 medially- and 1 laterally-located, toward the anterior margin on each side of the pronotum; and (3) 2 setae, 1 medially- and 1 laterally-located, midway between the anterior and posterior margins on each side of the pronotum. The metathoracic wing of the day 1 female was about as long as the elytron, and when the wing and elytron were folded ventrally around the pupa at the posterior end, the wing tip extended beyond that of the elytron (Fig. 8). The wing of the day 1 male was only approximatel:y one-half the size of the elytron, and did not extend beyond it when folded ventrally (Fig. 6). The metathoracic wing of a day 3 female pupa and a day 2 male pupa is shown in Figs. 17 and 18, respectively. The anterior pronotal horn of the male was not visible (Fig. 19). Day 2. The eyes and mandibles of the pupa were beginning to darken. The coxae, particularly the mesothoracic coxae, were larger and more clearly defined, and the posterior processes on the coxae had lengthened (Fig. 11). The anterior pronotal horn of the male first became visible (Fig. 20). Day 3. The eyes, mandibles, and maxillae stipes were dark, and the tibiae had begun to darken. The pupal cuticle became transparent, and the imago was visible beneath (Figs. 12, 13). The long processes on the prothoracic and mesothoracic coxae disappeared (Fig. 14). The anterior pronotal horn of the male was clearly demarcated (Fig. 15). Day 4. The imago emerged from the pupal cuticle (Fig. 15). Tanning and sclerotization continued and were completed within 1 day. The partially sclerotized elytron of an emerging male is shown in Fig. 16.
DISCUSSION Another recent study in our laboratory (Beeman and Norris, 1977a, b) showed that the developmental time to eclosion for male embryos was significantly (p < 0.05) longer than for female embryos (mean time from pole cell exclusion to eclosion was 106.5 vs. 103. 2 hr, respectively). Peleg and Norris (1973) reported that there was no significant difference in developmental time of male and female larvae through the 3 larval instars. Our results support this prior conclusion regarding larvae, and also indicate no difference in the developmental times of male and female pupae. Thus, for the period from eclosion through adult emerger~ce, there was no significant difference in overall developmental rate between
36
JOEL G. KINGSOLVERand DALE M. NORRIS
PLATE 3 FIG. 9. Ventral view of anterior thorax of a female day 1 pupa. Scale 50 t~m. F~G. 10. Head and prothorax of a female day 1 pupa. Scale -- 100 t~m. FIG. ll. Ventral view of anterior thorax of a female day 2 pupa. Scale 100 p.m. FIG. 12. Ventral view of anterior thorax of a female day 3 pupa. Imago is visible through pupal cuticle S c a l e - 100 t~m. males a n d females, a n d the q u a n t i t y o f genetic material in the h a p l o i d male thus was n o t a limiting factor in the overall d e v e l o p m e n t a l rates o f larva, p u p a , or adult. Peleg a n d N o r r i s 0 9 7 3 ) also r e p o r t e d t h a t male larvae c o u l d be reliably distinguished f r o m female larvae only in m a t u r e third instars. Such d e t e r m i n a t i o n s were m a d e on the basis o f h e a d - c a p s u l e width. O u r o b s e r v a t i o n s on d a y - - 3 (i.e., third instar) larvae also i n d i c a t e d that the female is a p p r o x i m a t e l y 25 ~ longer t h a n the male. Thus, by d a y - - 3 the sexual d i m o r p h i s m in overall b o d y size is a l r e a d y a p p a r e n t . H o w e v e r , the d a y - - 3 larva o f each sex is 20-30 ~ smaller t h a n the p u p a or adult.
Metamorphosis of Xyleborus
37
PLATE 4 Fit. 13. 12,orso-lateral view of pronotum of a female day 3 pupa. Adult setae (AS) are visible through pupal cuticle. PS, pupal setae. Scale = 100 #m. FIG. 14. Ventral view of pro- and mesothoracic coxae of a female day 3 pupa. Scale = 50 /~m. FIG. 15. Dorsal view of pronotum of a male day 4 pupa. Pupal cuticle has broken off on left side of adult pronotal horn (PH) and along posterior margin of pronotum. Scale = 100 p.m. FfG. 16. Dorsal view of partially sclerotized elytron of an emerging male. Scale = 100 /~m. Other m a j o r sexually d i m o r p h i c features in the p u p a include the metathoracic wing a n d p r o n o t u m . By day 0, the difference in size of the metathoracic wing between male a n d female was readily a p p a r e n t (Figs. 6, 8). A c o r r e s p o n d i n g size difference was also f o u n d in the wings of adults. The male adult, with its short degenerate wing (Fig. 18), is u n a b l e to
38
JOEL G. KINGS:)LVERand DALE M. NORRIS
PLATE 5
FIG. 17. Right elytron and metathoracic wing of a female day 3 pupa. The wing is about same length as elytron. Scale 100 ~m. FIG. 18. Right metathoracic wing of a male day 2 pupa. Wing extends only about halfway to posterior abdomen. Scale lO0 ~m. FIG. 19. Ventral view of anterior margin of pronotum (PN) and head of a male day 1 pupa. Pronotal horn is not visible. Scale -- 100 ~m. FIG. 20. Dorsal view of pronotum of a male day 2 pupa. Pronotal horn is just visible. Scale 100 t~m. fly; whereas, the female is a strong flier. The p r o n o t a l h o r n of the male, a p r o m i n e n t structure in this adult, was n o t visible on day 0 or day 1 (Fig. 19). It usually became visible by day 2 (Fig. 20), a n d was clearly evident by day 3 (Fig. 15). M e a s u r e m e n t s on the a n t e n n a , each thoracic leg, p r o n o t u m , a n d elytron indicated that these body parts are not significantly different (p < 0.05) in size in the day 1 p u p a a n d the adult. D a t a were b a s e d on 22 female a n d 17 male pupae, and 23 female a n d 22 male adults.
Metamarphosis of Xyleborus
39
The m e s o t h o r a c i c coxa in the d a y 1 p u p a is smaller (ca. 30-35 ~o) t h a n in the adult, but it is o f comparable, size by d a y 2 or 3. Because o f differences in form, c o m p a r i s o n s o f m o u t h parts were not m a d e . M o s t external p u p a l features are evident by d a y 0, a n d except for t a n n i n g a n d sclerotization, there is little further change until d a y 3. A n o t a b l e a n d interesting exception is the continuing d e v e l o p m e n t o f the male p r o n o t a l horn, because it becomes a m a j o r m o r p h o logical difference between male a n d female adults. A n o t h e r external p u p a l feature which u n d e r g o e s significant d e v e l o p m e n t d u r i n g the early p u p a l stage is the f o r m a n d lengthening o f the processes on the p r o - a n d m e s o t h o r a c i c coxae. These processes g r a d u a l l y disintegrate in the d a y 3 p u p a , a n d there is n o c o r r e s p o n d i n g structure in the a d u l t beetle. The setae on the d o r s a l a n d lateral p r o n o t u m , and a n t e r i o r to the l a b r u m also a p p e a r to be u n i q u e to the p u p a l stage. The setal p a t t e r n on the i m a g o is entirely different from that on the p u p a (Fig. 13). The i n f o r m a t i o n a b o u t X. ferrugineus d e v e l o p m e n t a n d m o r p h o l o g y p r o v i d e d in this paper, plus that previously p u b l i s h e d as cited, establishes the f o u n d a t i o n k n o w l e d g e necessary to use o f this unique a n i m a l system in m a n y types o f refined e x p e r i m e n t a l studies in d e v e l o p m e n t a l biology. Its usefulness in such future research m a y become second a m o n g insects only to Drosophila. Acknowledgemer, t--This research was supported by the Director of the Research Division, C.A.L.S., University of Wisconsin, Madison; and in part by research grant No. RR-00779 from the Division of Research Resources, National Institutes of Health, and by funds from the Schoenleber Foundation, Milwaukee, WI.
REFERENCES BEEMAN, S. L. alad D. M. NORRIS. 1977a. Embryogenesis of Xyleborusferrugineus. I. External morphology of male: and female embryo. J. Morphol. (in press). BEEMAN,S. L. and D. M. NORRIS. 1977b. Embryogenesis of Xyleborusferrugineus. II. Developmental rates of male and female embryos. J. Morphol. (in press). CHtJ, H. M. and D. M. NORRIS. 1976. Ultrastructure of the compound eye of the haploid male beetle Xylebo vusferrugineus. Cell Tissue Res. 168: 315-24. CHU, H. M., D. M. NORRISand S. D. CARLSON.1975. Ultrastructure of the compound eye of the diploid female beetle, Xyleborus ferrugineus. Cell Tissue Res. 165: 23-36. CHU, H. M., D. M. NORRISand L. T. KOK. 1970. Pupation requirement of the beetle, Xyleborusferrugineus: Sterols other than cholesterol. J. Inseet Physiol. 16: 1379-87. KINGSOLVER,J. G. and D. M. NORRIS. 1977. External morphology of Xyleborus ferrugineus. I. Head and protho tax of adult males. J. Morphol. (In press). NORRIS, D. M. 1972. Dependence of fertility and progeny development of Xyleborus ferrugineus upon chemicals from its symbiotes, pp. 299-310. In J. G. RODRIGUEZ(ed.) Insect and Mite Nutrition. North-Holland Co., Amsterdam. NORRIS, D. M. and H. M. CHtJ. 1970. Nutrition of Xyleborus ferrugineus. II. A holidic diet for the aposymbiotic insect. Ann. Entornol. Soe. Amer. 63:114245. PELE% B. and D. M. NORRIS. 1973. Haploid versus diploid Xyleborusferrugineus. I. Larval instars, development, and morphogenesis of the metathoracic wing. Ann. Entomol. Soc. Amer. 66: 180-83.