- Email: [email protected]
Foregut microspines in four families of cockroaches (Blattaria)
~/) Pergamon
Int. J. Insect Morphol. & Emh(vol. Vol. 23, No. 3, pp. 253-260, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved ()1120, 7322/94 $7.00 +0.(X)
F O R E G U T MICROSPINES IN F O U R FAMILIES OF COCKROACHES (BLATTARIA)
RICttARD J. ELZINGA and THEODORE L. HOPKINS Department of Entomology, Kansas State University, Manhattan, KS 66506, U.S.A.
(Accepted 7 July 1993)
Abstract--The microspines of the cockroach foregut were investigated in order to determine their fine structure, variation, patterns of distribution, and possible functions. The following were studied: Blaberidae (4 species), Blatellidae (3 species), Blattidae (2 species), and Cryptocercidae (one species). Elongate microspines (over 30/~m), usually several attached to a basal plate, were found in the buccal cavity and anterior and posterior pharynx of blaberids and blattids, whereas moderate (15-20/~m) to short (1-5/~m) miscrospines were found in 2 regions in the blanellid and cryptocercid cockroaches. Short microspines (1-5 p~m) individually attached to a basal plate occurred in the esophagus, crop, proventriculus and stomodeal valve regions in all families studied. Microspines appear to be useful in understanding systematics and evolution of cockroaches. The possible role of elongate microspines in retaining food particles during regurgitation behavior is postulated. Index descriptors (in addition to those in title): Blatteria, cockroaches, cuticular intima, foregut, microspines. INTRODUCTION THE PRESENCE of microspines on foregut cuticle of a c o c k r o a c h , Blatta orientalis, was first r e p o r t e d by Miall and D e n n y (1886) as "hairs (setae) of elongate, conical form, and often articulated at the base, like the large setae of the o u t e r skin". In the esophagus, the hairs were very long and g r o u p e d in bundles along a sinuous transverse line, but they b e c a m e shorter in the crop. T h e y also stated that the hairs were directed posteriorly and p r o b a b l y served as a guide for the flow of saliva. T h e s e " h a i r s " are n o w referred to as microspines. Microspines in the proventriculus (to a very m i n o r degree) and the large proventricular tooth modifications (Snodgrass, 1935; Judd, 1948) have been used as diagnostic characters in cockroach classification and keys (McKittrick, 1964; Miller a~d Fisk, 1971; H u b e r , 1974; Fisk, 1987). Using light microscopy, M u r t h y (1975) r e p o r t e d that the foregut cuticle of Periplaneta americana had longer microspines in the p h a r y n x than in the crop. Similar research on o t h e r c o c k r o a c h species has not been reported. Also, the use of the m o r e efficient Scanning Electron Microscope ( S E M ) to study c o c k r o a c h microspines has been limited to 2 micrographs f r o m P. americana (Bracke et al., 1979). W e have used S E M to examine the fine structure, variation, and patterns of microspines located on the cuticular surface of the buccal cavity, pharynx, esophagus, crop, and s t o m o d e a l valve (as defined by Snodgrass, 1935) of representative species in 4 families of cockroaches. 253
254
R . J . ELZINGA and T. L. HOPKINS
MATERIALS AND METHODS The lollowing cockroach families and species were studied: Cryptocercidae: Cryptocercus punctulatus Scudder: Blanidae: Periplaneta americana (L.); Blatta orientalis L.; Blattellidae: Parcoblatta pennsylvanica (DeGeer); Blattella germanica (L.); Supella Iongipalpa (Fab.): and Blaberidae: Blaberus craniifer Burmeister" Gromphadorhina portentosa (Schaum); Leucophaea maderae (Fab,); and Nauphoeta cinerea (Oliver). These species were selected because they represent distant relationships within families and subfamilies as presented by McKittrick (1964) and Huber (1974) and, most likely, would include possible variation. All specimens were obtained from Kansas State University cultures, except P. pennsylvanica, which was collected at Pillsbury Crossing, Riley County, Kansas, and Crvptocercus punctulatus, which was provided by Christine Nalepa, North Carolina State University. Adult cockroaches were randomly culled and fixed in Kahle's solution. Each head was removed and sectioned sagittally, but the foregut was left in position to ensure accurate correlations between observations and specific sections of the gut. The remainder of the foregut was dissected and sectioned along the dorsal meson, Gut contents were removed, and the exposed intima was brushed with an artist's paint brush whose libers had been cut short to obtain rigidity. Subsequently, detergent was added and the gut soaked for 30 min, then the intima brushed again and flushed 4 or 5 times with distilled water forcibly ejected from a narrow-diameter pipette. The cleansed foreguts were transferred to dry Petri dishes, spread open, and covered with microscope slide fragments to prevent curling. The specimens were then dehydrated using an ethyl alcohol series and left to dry within the closed Petri dish. Once dry, each foregut was cut into sections and transferred to SEM stubs, sputter-coated with gold palladium, and finally viewed in an ETEC Autoscan electron microscope.
RESULTS
Buccal cavity and p h a r y n x M i c r o s p i n e s in these 2 sections of the f o r e g u t often a r o s e at the p o s t e r i o r b o r d e r of a scalelike s u b s e c t i o n ( s o m e t i m e s difficult to distinguish) o f i n t i m a (Figs 1-4). T h e s e units will h e n c e f o r t h be r e f e r r e d to as m u l t i s p i n o s e w h e n m o r e t h a n o n e m i c r o s p i n e was f o u n d p e r " s c a l e " and unispinose if only one was p r e s e n t . T h e s e spines v a r i e d in length on a g r a d i e n t f r o m short (1-5 # m ) to m o d e r a t e ( 1 5 - 2 0 / z m ) to long ( o v e r l a p p i n g o n e a n o t h e r sufficiently such that length c o u l d not be definitely d e t e r m i n e d but w e r e at least 3 0 # m ) . A l l spines p r o j e c t e d p o s t e r i o r l y in t h e s e 2 regions. A s in all r e g i o n s h e r e i n r e p o r t e d , t h e r e w e r e no c o r r e l a t i o n s b e t w e e n m i c r o s p i n e size a n d the size o f the r o a c h b e i n g studied. M i c r o s p i n e s first a p p e a r e d a b r u p t l y in the a n t e r i o r p o r t i o n of the buccal cavity. W h e n the d o r s a l m i c r o s p i n e s w e r e long, the l a t e r a l a n d v e n t r a l o n e s w e r e initially s h o r t , but the f o r m e r usually b e c a m e e l o n g a t e p r i o r to r e a c h i n g the a n t e r i o r p h a r y n x . T h e r e v e r s e possibility, the p r e s e n c e of long l a t e r a l a n d v e n t r a l m i c r o s p i n e s a n d s h o r t e n e d d o r s a l ones, was n e v e r o b s e r v e d . T h e s h a p e a n d size o f m i c r o s p i n e s f o u n d in the buccal cavity c o r r e l a t e d closely with those of spines l o c a t e d in b o t h the a n t e r i o r a n d p o s t e r i o r p h a r y n x regions. C o c k r o a c h species classified within the s a m e family h a d similar m i c r o s p i n a l d e v e l o p m e n t . W i t h the e x c e p t i o n of B. craniifer, which h a d m o d e r a t e l y long m i c r o s p i n e s a n d was m u l t i s p i n o s e (Fig. 1), the B l a b e r i d a e p o s s e s s e d n u m e r o u s long uni- o r m u l t i s p i n o s e ( " s h a v i n g " small a r e a s p e r m i t t e d this to be seen) spines, t h e o v e r a l l a p p e a r a n c e b e i n g o n e of a c o n t i n u o u s brush. This d i f f e r e n c e is c o r r e l a t e d with the d i s t a n t s e p a r a t i o n o f Blaberus f r o m the o t h e r 3 species s t u d i e d into d i f f e r e n t s u b f a m i l i e s as p r e s e n t e d by M c K i t t r i c k (1964). T h e B l a t t i d a e also h a d e l o n g a t e m i c r o s p i n e s (Fig. 2), but the l a t e r a l a n d v e n t r a l o n e s were usually o n l y m o d e r a t e l y long (Fig. 3). T h e B l a t t e l l i d a e (Fig. 4) a n d C r y p t o c e r c i d a e p o s s e s s e d only s h o r t m i c r o s p i n e s t h e r e b y p e r m i t t i n g t h e i r distinct scalelike base and m u l t i s p i n o s e c o n d i t i o n to be easily seen.
Foregut Microspines in Cockroaches
255
FIG. 1. Blaberus craniifer. Pharynx with some microspines "shaved" off to expose their origins. Anterior is to left as in all subsequent figures, s = scalelike base, Bar = 3.3/xm. FIG. 2. Biatta orientalis. Pharynx with overlapping elongate microspines. Bar = 3.3/.tm. FIG. 3. Periplaneta americana. Pharynx, lateral microspines, s = scalelike base. Bar = 3.3 p.m. FlG. 4. Supella longipalpa. Pharynx. s = scalelike base. Bar = 3.0/xm.
E s o p h a g u s and crop T h e c r o p i~ o r t h o p t e r o i d insects r e p r e s e n t s an e n l a r g e m e n t o f the p r i m i t i v e e s o p h a g u s ; t h e r e f o r e , o n e w o u l d e x p e c t the m i c r o s p i n a l d e v e l o p m e n t to b e q u i t e s i m i l a r in t h e s e 2 s e c t i o n s of t h e f o r e g u t ; this p r o v e d to be t h e case. M i c r o s p i n e s , including t h e i r bases, f o u n d in t h e s e 2 sections d i f f e r e d m a r k e d l y in all s p e c i e s s t u d i e d f r o m t h o s e o b s e r v e d in the buccal cavity a n d p h a r y n x . G e n e r a l l y , m i c r o s p i n e s p r o j e c t e d p o s t e r i o r l y , e x c e p t t h o s e l o c a t e d at the p o s t e r i o r p a r t o f t h e c r o p n e a r the p r o v e n t r i c u l u s , which w e r e d i r e c t e d a n t e r i o r l y . In B l a b e r i d a e , the m i c r o s p i n e s w e r e o n l y of m o d e r a t e l e n g t h a n d w e r e m u l t i s p i n o s e in the e s o p h a g u s a n d the e x t r e m e a n t e r i o r p a r t o f t h e c r o p , b u t t h e y t h e n s h o r t e n e d q u i c k l y a n d b e c a m e u n i s p i n o s e with v e r y s h o r t b a s e s (Fig. 5). T h i s . s h o r t e n e d ,
256
R.J. ELZZN6Aand T. L. HOPKINS
Fie;. 5. Leucophaea maderae. Anterior part of crop. s = scalelike base. Bar = 3.3/zm. Fic;. 6. Nauphoeta cinerea. Posterior region of crop with microspines projecting anteriorly. Bar = 3.3/xm.
u n i s p i n o s e c o n d i t i o n was r e t a i n e d to the j u n c t i o n b e t w e e n the c r o p a n d p r o v e n t r i c u l u s (Fig. 6). T h e b l a t t i d m i c r o s p i n e s within these 2 regions w e r e initially similar to t h o s e l o c a t e d in the p h a r y n x a n d t h e n s h o r t e n e d in the e x t r e m e a n t e r i o r p o r t i o n of the c r o p , but the c o n t r a s t was not as distinct as in the b l a b e r i d s . A few i s o l a t e d m i c r o s p i n e s o f m o d e r a t e length w e r e l o c a t e d a n t e r i o r l y (Fig. 7). T h e spines w e r e usually s h o r t a n d u n i s p i n o s e t h r o u g h o u t the crop. T h e s p i n e l i k e base f o u n d in the m i c r o s p i n e s of c r y p t o c e r c i d p h a r y n x s h o r t e n e d in the e s o p h a g u s a n d b e c a m e o b s c u r e d by n u m e r o u s folds (Fig. 8); t h e r e f o r e , the multispinose c o n d i t i o n was e v i d e n t only by e x t r a p o l a t i n g the p h a r y n x state to this region. T h e s e m o d i f i c a t i o n s w e r e c o n t i n u e d t h r o u g h o u t the c r o p , e x c e p t in the p o s t e r i o r p o r t i o n w h e r e the m i c r o s p i n e s b e c a m e slightly longer. T h e g r e a t e s t v a r i a t i o n in c r o p m i c r o s p i n e s was f o u n d a m o n g t h e B l a t t e l l i d a e , a n d this c o r r e l a t e d with M c K i t t r i c k ' s (1964) p l a c e m e n t of the 2 species s t u d i e d into s e p a r a t e subfamilies. In S. Iongipalpa, m a n y of the m i c r o s p i n e s w e r e m o d e r a t e l y e l o n g a t e in the m i d c r o p , w h e r e a s those o b s e r v e d in P. p e n n s y l v a n i c a a n d B. germanica w e r e s h o r t e n e d with the scalelike base b e c o m i n g indistinct (Fig. 9), as seen in the B l a b e r i d a e .
Fie. 7. Periplaneta americana. Anterior region of crop. Bar - 5.0/zm. FI~;. 8. Cryptocercus punctulatus. Anterior part of crop. s = scalelikc base. Bar - 3.3/~m. Flt~. 9. Blattella germanica. Mid crop. Bar = 3.3/xm. FI~;. 10. Leucophaea maderae. Multisetose microspines on tip of proventricular tooth. Bar - 33.0/zm. FIG. 11. Nauphoeta cinerea. Proventricular microspines. Bar 3.3/xm. FI~. 12. Gromphadorhina portentosa. Multisetose microspines on tip of proventricular tooth. Bar - 3.3/zm.
=t"
0
258
R.J. ELZINGAand T. L. HOPKINS
Proventriculus and stomodeal valve As indicated earlier, the macro structures of the proventriculus (proventricular teeth, etc.) have been well studied, particularly by Judd (1948), McKittrick (1964), and Miller and Fisk (1971), whereas the microspines have received considerably less study. Although this study did not initially intend to include the "microtrichia" (enlarged microspines) of the pads and interdentary zones of Miller and Fisk (1971), some cursory information must be reported, because the microspines of these 2 regions reflect the continuum of spines throughout the foregut. In the Blaberidae, where the proventricular teeth are poorly specialized, the microspines were slightly longer than those found in the crop and varied from multi- to unispinose, often on the same proventricular tooth (Figs 10-12). The stomodeal valve had similarly developed spines and patterns to those found on the proventricular teeth. In N. cinerea, the microspines were separated from one another in both of these 2 regions (Fig. 11) and were essentially identical. The proventricular teeth were much more specialized and sclerotized in the Blattidae than in the Blaberidae. Between the proventricular teeth were rows of short or elongate "microtrichia", as noted previously; however, many of these had branches or tines (Fig. 13). The large sclerotized teeth possessed scalelike microspines, but these were found usually at the tips of the teeth and not continuously over their entire surface. In C. punctulatus, with their slender, short proventricular teeth, multispinose microspines were normally located only between the teeth and became shortened in the stomodeal valve area (Fig. 14). Large scalelike microspines were found at the tips of the bladelike proventricular teeth in the Blattellidae. Also, both multi- and unispinose microspines were arranged in rows between the teeth and on the pads. The stomodeal valve lacked microspines in B. germanica, but possessed minute microspines in P. pennsylvanica.
DISCUSSION A continuum of microspines was found throughout the foregut, except for the basal sections of the large sclerotized proventricular teeth and the stomodeal valve in B. germanica. With the exception of the proventricular "microtrichia," the longest microspines (at least 30 p.m) in the multispinose condition were located in the buccal cavity and pharynx, while the shortest spines, usually in the unispinose state, were found in the crop and stomodeal valve. Boudreaux (1980) and Chapman (1985) discussed the modifications of proventricular microspines or acanthae in different insect orders and indicated their potential use in systematics, particularly where relationships are conjectural; but what of those found in other sections of the foregut? The presence of short, umspinose and often sparse microspines in the pharyngeal region of primitive insects such as Thysanura, Odonata, and Ephemeroptera (Elzinga, unpublished data) demonstrates the ground plan for microspines in the head foregut. Our finding of the more advanced multispinose condition with short spines in the primitive Cryptocercus punctulatus and in the Blatellidae, both of which are placed on separate branches of the phyiogram of McKittrick (1964), demonstrates the character advance for cockroaches. Further, the
Foregut Microspinesin Cockroaches
259
FIG. 13. Periplaneta americana. Microtrichialtips between proventricular teeth. Bar = 3.3/~m. FIG. 14. Cryptocercus punctulatus. Stomodeal valve, s = scalelike base. Bar = 3.3/xm.
presence of elc,ngate, multispinose microspines in the pharynx and buccal cavity of both the Blattidae and the highly advanced Blaberidae, each placed on separate branches by McKittrick, suggests that this lengthened condition must have evolved at least twice. Yet, variation in the structure and patterns of microspines within families appears to be minimal and supports the conclusions of both McKittrick (1964) and H u b e r (1974). Therefore, microspines of the nonproventricular foregut appear to support the current classification of cockroaches and provide an additional tool in understanding evolution in this taxon. The adaptive function of microspines is speculative, but they most likely aid in the movement of food posteriorly in the pharynx and esophagus and the grinding of food by the proven~Lriculus (Chapman, 1985). Microspines in the cockroach crop may also assist in mixing of food with digestive enzymes and fluid from the salivary glands and midgut secretions during peristalsis. The pharyngeal spines of P. americana are apparently tanned and therefore stiffened, whereas their bases were untanned as determined b2~ staining (Murthy, 1975). Spines on the proventricular teeth are also sclerotized or tanned for grinding operations (Chapman, 1985). Microspines or acanthae are common in orthopteroid insects and several other orders that have been examined (Muralirangan and Ananthakrishnan, 1974; Boudreaux, 1980; Hochuli et al., 1992). A likely additional function for the lengthened microspines and/or multispinose condition is that these spines, in collaboration with the narrowed and muscular pharyngeal regions, are acting as a natural valve to prevent the regurgitation and loss of ingested food. Rather than using regurgitation extensively as a specialized means of defense as grasshoppers do, some cockroaches may rely on defecation to repel predators. Therefore, the distinct possibility exists that microspinal structure and distribution in cockroach foregut have been under at least a dual selection, for moving food posteriorly within the crop (with its concurrent mixing action) and for retaining ingested food within the crop by inhibiting regurgitation.
260
R . J . ELZINGA and T. L. HOPKINS
Acknowledgements--We thank John Krchma for S.E.M. work and Sharon Starkey for rearing and supplying most of the cockroach species used in this study (both of the Department of Entomology, Kansas State University). Thanks to Christina Nalepa, North Carolina State University, Raleigh, NC for supplying C. punctulatus. This publication is Contribution No. 93-413-J of the Kansas Agricultural Experiment Station, Kansas State University. The research was supported in part by Hatch Projects H033 and H548. REFERENCES BOUDREAUX, H. B. 1980. Proventricular acanthae and their phylogenetic implications. Ann. Entomol. Soc. Amer. 73(2): 189-96. BRACKE, J. W., D. L. CRUDEN and A. D. MARKOVETZ. 1979. Intestinal microbial flora of the American cockroach, Periplaneta americana L. Appl. Environ. Microbiol. 38: 945-55. CHAPMAN,R. F. 1985. Structure of the Digestive System, pp. 165-211. In G. A. KERKUTand L. I. GILBERT (eds.) Comprehensive Insect Physiology and Pharmacology, Vol. 4. Pergamon Press, Oxford. FisK, F. W. 1987. Order Blattodea. In F. W. STEHR (ed.) Immature Insects, Vol. I, Kendall/Hunt Publ. Co., Dubuque. Hocm, Ll, D. F., B. ROBERTS and G. D. SANSON. 1992. Anteriorly directed microspines in the foregut of Locusta migratoria (Orthoptera : Acrididae). Int. J. Insect Morphol. Embryol. 21(I): 95-7. HUBER, I. 1974. Taxonomic and ontogenetic studies of cockroaches (Blattaria). Univ. Kansas Sci. Bull. 50(6): 233-332. JUDD, W. W. 1948. A comparative study of the proventriculus of orthopteroid insects with reference to its use in taxonomy. Can. J. Res. D. 26: 93-161. McKITrR~CK, F. A. 1964. Evolutionary studies of cockroaches. Cornell Univ. Agric. Exp. Stn. Mem. 389: 1-197. MIALL, L. C. and A. DENNY. 1886. The Structure and Life History of the Cockroach (Periplaneta orientalis). Lovell Reeve Co., London. M,.LER, H. K. and F. W. FISK. 1971. Taxonomic implications of the comparative morphology of cockroach proventriculi. Ann. Entomol. Soc. Amer. 64(3): 671-87. MURALIRANGAN,M. C. and T. N. ANANTHAKRISHNAN. 1974. Taxonomic significance of the foregut armature in some Indian Acridoidea (Orthoptera). Orient. Insects 8:119--45. MURTHV, R. C. 1975. Structure of the foregut cuticle of Periplaneta americana. Experientia 32: 316-17. SNODGRASS, R. E. 1935. Principles" oflnsect Morphology. McGraw-Hill Book Co., New York.
Int. J. Insect Morphol. & Emh(vol. Vol. 23, No. 3, pp. 253-260, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved ()1120, 7322/94 $7.00 +0.(X)
F O R E G U T MICROSPINES IN F O U R FAMILIES OF COCKROACHES (BLATTARIA)
RICttARD J. ELZINGA and THEODORE L. HOPKINS Department of Entomology, Kansas State University, Manhattan, KS 66506, U.S.A.
(Accepted 7 July 1993)
Abstract--The microspines of the cockroach foregut were investigated in order to determine their fine structure, variation, patterns of distribution, and possible functions. The following were studied: Blaberidae (4 species), Blatellidae (3 species), Blattidae (2 species), and Cryptocercidae (one species). Elongate microspines (over 30/~m), usually several attached to a basal plate, were found in the buccal cavity and anterior and posterior pharynx of blaberids and blattids, whereas moderate (15-20/~m) to short (1-5/~m) miscrospines were found in 2 regions in the blanellid and cryptocercid cockroaches. Short microspines (1-5 p~m) individually attached to a basal plate occurred in the esophagus, crop, proventriculus and stomodeal valve regions in all families studied. Microspines appear to be useful in understanding systematics and evolution of cockroaches. The possible role of elongate microspines in retaining food particles during regurgitation behavior is postulated. Index descriptors (in addition to those in title): Blatteria, cockroaches, cuticular intima, foregut, microspines. INTRODUCTION THE PRESENCE of microspines on foregut cuticle of a c o c k r o a c h , Blatta orientalis, was first r e p o r t e d by Miall and D e n n y (1886) as "hairs (setae) of elongate, conical form, and often articulated at the base, like the large setae of the o u t e r skin". In the esophagus, the hairs were very long and g r o u p e d in bundles along a sinuous transverse line, but they b e c a m e shorter in the crop. T h e y also stated that the hairs were directed posteriorly and p r o b a b l y served as a guide for the flow of saliva. T h e s e " h a i r s " are n o w referred to as microspines. Microspines in the proventriculus (to a very m i n o r degree) and the large proventricular tooth modifications (Snodgrass, 1935; Judd, 1948) have been used as diagnostic characters in cockroach classification and keys (McKittrick, 1964; Miller a~d Fisk, 1971; H u b e r , 1974; Fisk, 1987). Using light microscopy, M u r t h y (1975) r e p o r t e d that the foregut cuticle of Periplaneta americana had longer microspines in the p h a r y n x than in the crop. Similar research on o t h e r c o c k r o a c h species has not been reported. Also, the use of the m o r e efficient Scanning Electron Microscope ( S E M ) to study c o c k r o a c h microspines has been limited to 2 micrographs f r o m P. americana (Bracke et al., 1979). W e have used S E M to examine the fine structure, variation, and patterns of microspines located on the cuticular surface of the buccal cavity, pharynx, esophagus, crop, and s t o m o d e a l valve (as defined by Snodgrass, 1935) of representative species in 4 families of cockroaches. 253
254
R . J . ELZINGA and T. L. HOPKINS
MATERIALS AND METHODS The lollowing cockroach families and species were studied: Cryptocercidae: Cryptocercus punctulatus Scudder: Blanidae: Periplaneta americana (L.); Blatta orientalis L.; Blattellidae: Parcoblatta pennsylvanica (DeGeer); Blattella germanica (L.); Supella Iongipalpa (Fab.): and Blaberidae: Blaberus craniifer Burmeister" Gromphadorhina portentosa (Schaum); Leucophaea maderae (Fab,); and Nauphoeta cinerea (Oliver). These species were selected because they represent distant relationships within families and subfamilies as presented by McKittrick (1964) and Huber (1974) and, most likely, would include possible variation. All specimens were obtained from Kansas State University cultures, except P. pennsylvanica, which was collected at Pillsbury Crossing, Riley County, Kansas, and Crvptocercus punctulatus, which was provided by Christine Nalepa, North Carolina State University. Adult cockroaches were randomly culled and fixed in Kahle's solution. Each head was removed and sectioned sagittally, but the foregut was left in position to ensure accurate correlations between observations and specific sections of the gut. The remainder of the foregut was dissected and sectioned along the dorsal meson, Gut contents were removed, and the exposed intima was brushed with an artist's paint brush whose libers had been cut short to obtain rigidity. Subsequently, detergent was added and the gut soaked for 30 min, then the intima brushed again and flushed 4 or 5 times with distilled water forcibly ejected from a narrow-diameter pipette. The cleansed foreguts were transferred to dry Petri dishes, spread open, and covered with microscope slide fragments to prevent curling. The specimens were then dehydrated using an ethyl alcohol series and left to dry within the closed Petri dish. Once dry, each foregut was cut into sections and transferred to SEM stubs, sputter-coated with gold palladium, and finally viewed in an ETEC Autoscan electron microscope.
RESULTS
Buccal cavity and p h a r y n x M i c r o s p i n e s in these 2 sections of the f o r e g u t often a r o s e at the p o s t e r i o r b o r d e r of a scalelike s u b s e c t i o n ( s o m e t i m e s difficult to distinguish) o f i n t i m a (Figs 1-4). T h e s e units will h e n c e f o r t h be r e f e r r e d to as m u l t i s p i n o s e w h e n m o r e t h a n o n e m i c r o s p i n e was f o u n d p e r " s c a l e " and unispinose if only one was p r e s e n t . T h e s e spines v a r i e d in length on a g r a d i e n t f r o m short (1-5 # m ) to m o d e r a t e ( 1 5 - 2 0 / z m ) to long ( o v e r l a p p i n g o n e a n o t h e r sufficiently such that length c o u l d not be definitely d e t e r m i n e d but w e r e at least 3 0 # m ) . A l l spines p r o j e c t e d p o s t e r i o r l y in t h e s e 2 regions. A s in all r e g i o n s h e r e i n r e p o r t e d , t h e r e w e r e no c o r r e l a t i o n s b e t w e e n m i c r o s p i n e size a n d the size o f the r o a c h b e i n g studied. M i c r o s p i n e s first a p p e a r e d a b r u p t l y in the a n t e r i o r p o r t i o n of the buccal cavity. W h e n the d o r s a l m i c r o s p i n e s w e r e long, the l a t e r a l a n d v e n t r a l o n e s w e r e initially s h o r t , but the f o r m e r usually b e c a m e e l o n g a t e p r i o r to r e a c h i n g the a n t e r i o r p h a r y n x . T h e r e v e r s e possibility, the p r e s e n c e of long l a t e r a l a n d v e n t r a l m i c r o s p i n e s a n d s h o r t e n e d d o r s a l ones, was n e v e r o b s e r v e d . T h e s h a p e a n d size o f m i c r o s p i n e s f o u n d in the buccal cavity c o r r e l a t e d closely with those of spines l o c a t e d in b o t h the a n t e r i o r a n d p o s t e r i o r p h a r y n x regions. C o c k r o a c h species classified within the s a m e family h a d similar m i c r o s p i n a l d e v e l o p m e n t . W i t h the e x c e p t i o n of B. craniifer, which h a d m o d e r a t e l y long m i c r o s p i n e s a n d was m u l t i s p i n o s e (Fig. 1), the B l a b e r i d a e p o s s e s s e d n u m e r o u s long uni- o r m u l t i s p i n o s e ( " s h a v i n g " small a r e a s p e r m i t t e d this to be seen) spines, t h e o v e r a l l a p p e a r a n c e b e i n g o n e of a c o n t i n u o u s brush. This d i f f e r e n c e is c o r r e l a t e d with the d i s t a n t s e p a r a t i o n o f Blaberus f r o m the o t h e r 3 species s t u d i e d into d i f f e r e n t s u b f a m i l i e s as p r e s e n t e d by M c K i t t r i c k (1964). T h e B l a t t i d a e also h a d e l o n g a t e m i c r o s p i n e s (Fig. 2), but the l a t e r a l a n d v e n t r a l o n e s were usually o n l y m o d e r a t e l y long (Fig. 3). T h e B l a t t e l l i d a e (Fig. 4) a n d C r y p t o c e r c i d a e p o s s e s s e d only s h o r t m i c r o s p i n e s t h e r e b y p e r m i t t i n g t h e i r distinct scalelike base and m u l t i s p i n o s e c o n d i t i o n to be easily seen.
Foregut Microspines in Cockroaches
255
FIG. 1. Blaberus craniifer. Pharynx with some microspines "shaved" off to expose their origins. Anterior is to left as in all subsequent figures, s = scalelike base, Bar = 3.3/xm. FIG. 2. Biatta orientalis. Pharynx with overlapping elongate microspines. Bar = 3.3/.tm. FIG. 3. Periplaneta americana. Pharynx, lateral microspines, s = scalelike base. Bar = 3.3 p.m. FlG. 4. Supella longipalpa. Pharynx. s = scalelike base. Bar = 3.0/xm.
E s o p h a g u s and crop T h e c r o p i~ o r t h o p t e r o i d insects r e p r e s e n t s an e n l a r g e m e n t o f the p r i m i t i v e e s o p h a g u s ; t h e r e f o r e , o n e w o u l d e x p e c t the m i c r o s p i n a l d e v e l o p m e n t to b e q u i t e s i m i l a r in t h e s e 2 s e c t i o n s of t h e f o r e g u t ; this p r o v e d to be t h e case. M i c r o s p i n e s , including t h e i r bases, f o u n d in t h e s e 2 sections d i f f e r e d m a r k e d l y in all s p e c i e s s t u d i e d f r o m t h o s e o b s e r v e d in the buccal cavity a n d p h a r y n x . G e n e r a l l y , m i c r o s p i n e s p r o j e c t e d p o s t e r i o r l y , e x c e p t t h o s e l o c a t e d at the p o s t e r i o r p a r t o f t h e c r o p n e a r the p r o v e n t r i c u l u s , which w e r e d i r e c t e d a n t e r i o r l y . In B l a b e r i d a e , the m i c r o s p i n e s w e r e o n l y of m o d e r a t e l e n g t h a n d w e r e m u l t i s p i n o s e in the e s o p h a g u s a n d the e x t r e m e a n t e r i o r p a r t o f t h e c r o p , b u t t h e y t h e n s h o r t e n e d q u i c k l y a n d b e c a m e u n i s p i n o s e with v e r y s h o r t b a s e s (Fig. 5). T h i s . s h o r t e n e d ,
256
R.J. ELZZN6Aand T. L. HOPKINS
Fie;. 5. Leucophaea maderae. Anterior part of crop. s = scalelike base. Bar = 3.3/zm. Fic;. 6. Nauphoeta cinerea. Posterior region of crop with microspines projecting anteriorly. Bar = 3.3/xm.
u n i s p i n o s e c o n d i t i o n was r e t a i n e d to the j u n c t i o n b e t w e e n the c r o p a n d p r o v e n t r i c u l u s (Fig. 6). T h e b l a t t i d m i c r o s p i n e s within these 2 regions w e r e initially similar to t h o s e l o c a t e d in the p h a r y n x a n d t h e n s h o r t e n e d in the e x t r e m e a n t e r i o r p o r t i o n of the c r o p , but the c o n t r a s t was not as distinct as in the b l a b e r i d s . A few i s o l a t e d m i c r o s p i n e s o f m o d e r a t e length w e r e l o c a t e d a n t e r i o r l y (Fig. 7). T h e spines w e r e usually s h o r t a n d u n i s p i n o s e t h r o u g h o u t the crop. T h e s p i n e l i k e base f o u n d in the m i c r o s p i n e s of c r y p t o c e r c i d p h a r y n x s h o r t e n e d in the e s o p h a g u s a n d b e c a m e o b s c u r e d by n u m e r o u s folds (Fig. 8); t h e r e f o r e , the multispinose c o n d i t i o n was e v i d e n t only by e x t r a p o l a t i n g the p h a r y n x state to this region. T h e s e m o d i f i c a t i o n s w e r e c o n t i n u e d t h r o u g h o u t the c r o p , e x c e p t in the p o s t e r i o r p o r t i o n w h e r e the m i c r o s p i n e s b e c a m e slightly longer. T h e g r e a t e s t v a r i a t i o n in c r o p m i c r o s p i n e s was f o u n d a m o n g t h e B l a t t e l l i d a e , a n d this c o r r e l a t e d with M c K i t t r i c k ' s (1964) p l a c e m e n t of the 2 species s t u d i e d into s e p a r a t e subfamilies. In S. Iongipalpa, m a n y of the m i c r o s p i n e s w e r e m o d e r a t e l y e l o n g a t e in the m i d c r o p , w h e r e a s those o b s e r v e d in P. p e n n s y l v a n i c a a n d B. germanica w e r e s h o r t e n e d with the scalelike base b e c o m i n g indistinct (Fig. 9), as seen in the B l a b e r i d a e .
Fie. 7. Periplaneta americana. Anterior region of crop. Bar - 5.0/zm. FI~;. 8. Cryptocercus punctulatus. Anterior part of crop. s = scalelikc base. Bar - 3.3/~m. Flt~. 9. Blattella germanica. Mid crop. Bar = 3.3/xm. FI~;. 10. Leucophaea maderae. Multisetose microspines on tip of proventricular tooth. Bar - 33.0/zm. FIG. 11. Nauphoeta cinerea. Proventricular microspines. Bar 3.3/xm. FI~. 12. Gromphadorhina portentosa. Multisetose microspines on tip of proventricular tooth. Bar - 3.3/zm.
=t"
0
258
R.J. ELZINGAand T. L. HOPKINS
Proventriculus and stomodeal valve As indicated earlier, the macro structures of the proventriculus (proventricular teeth, etc.) have been well studied, particularly by Judd (1948), McKittrick (1964), and Miller and Fisk (1971), whereas the microspines have received considerably less study. Although this study did not initially intend to include the "microtrichia" (enlarged microspines) of the pads and interdentary zones of Miller and Fisk (1971), some cursory information must be reported, because the microspines of these 2 regions reflect the continuum of spines throughout the foregut. In the Blaberidae, where the proventricular teeth are poorly specialized, the microspines were slightly longer than those found in the crop and varied from multi- to unispinose, often on the same proventricular tooth (Figs 10-12). The stomodeal valve had similarly developed spines and patterns to those found on the proventricular teeth. In N. cinerea, the microspines were separated from one another in both of these 2 regions (Fig. 11) and were essentially identical. The proventricular teeth were much more specialized and sclerotized in the Blattidae than in the Blaberidae. Between the proventricular teeth were rows of short or elongate "microtrichia", as noted previously; however, many of these had branches or tines (Fig. 13). The large sclerotized teeth possessed scalelike microspines, but these were found usually at the tips of the teeth and not continuously over their entire surface. In C. punctulatus, with their slender, short proventricular teeth, multispinose microspines were normally located only between the teeth and became shortened in the stomodeal valve area (Fig. 14). Large scalelike microspines were found at the tips of the bladelike proventricular teeth in the Blattellidae. Also, both multi- and unispinose microspines were arranged in rows between the teeth and on the pads. The stomodeal valve lacked microspines in B. germanica, but possessed minute microspines in P. pennsylvanica.
DISCUSSION A continuum of microspines was found throughout the foregut, except for the basal sections of the large sclerotized proventricular teeth and the stomodeal valve in B. germanica. With the exception of the proventricular "microtrichia," the longest microspines (at least 30 p.m) in the multispinose condition were located in the buccal cavity and pharynx, while the shortest spines, usually in the unispinose state, were found in the crop and stomodeal valve. Boudreaux (1980) and Chapman (1985) discussed the modifications of proventricular microspines or acanthae in different insect orders and indicated their potential use in systematics, particularly where relationships are conjectural; but what of those found in other sections of the foregut? The presence of short, umspinose and often sparse microspines in the pharyngeal region of primitive insects such as Thysanura, Odonata, and Ephemeroptera (Elzinga, unpublished data) demonstrates the ground plan for microspines in the head foregut. Our finding of the more advanced multispinose condition with short spines in the primitive Cryptocercus punctulatus and in the Blatellidae, both of which are placed on separate branches of the phyiogram of McKittrick (1964), demonstrates the character advance for cockroaches. Further, the
Foregut Microspinesin Cockroaches
259
FIG. 13. Periplaneta americana. Microtrichialtips between proventricular teeth. Bar = 3.3/~m. FIG. 14. Cryptocercus punctulatus. Stomodeal valve, s = scalelike base. Bar = 3.3/xm.
presence of elc,ngate, multispinose microspines in the pharynx and buccal cavity of both the Blattidae and the highly advanced Blaberidae, each placed on separate branches by McKittrick, suggests that this lengthened condition must have evolved at least twice. Yet, variation in the structure and patterns of microspines within families appears to be minimal and supports the conclusions of both McKittrick (1964) and H u b e r (1974). Therefore, microspines of the nonproventricular foregut appear to support the current classification of cockroaches and provide an additional tool in understanding evolution in this taxon. The adaptive function of microspines is speculative, but they most likely aid in the movement of food posteriorly in the pharynx and esophagus and the grinding of food by the proven~Lriculus (Chapman, 1985). Microspines in the cockroach crop may also assist in mixing of food with digestive enzymes and fluid from the salivary glands and midgut secretions during peristalsis. The pharyngeal spines of P. americana are apparently tanned and therefore stiffened, whereas their bases were untanned as determined b2~ staining (Murthy, 1975). Spines on the proventricular teeth are also sclerotized or tanned for grinding operations (Chapman, 1985). Microspines or acanthae are common in orthopteroid insects and several other orders that have been examined (Muralirangan and Ananthakrishnan, 1974; Boudreaux, 1980; Hochuli et al., 1992). A likely additional function for the lengthened microspines and/or multispinose condition is that these spines, in collaboration with the narrowed and muscular pharyngeal regions, are acting as a natural valve to prevent the regurgitation and loss of ingested food. Rather than using regurgitation extensively as a specialized means of defense as grasshoppers do, some cockroaches may rely on defecation to repel predators. Therefore, the distinct possibility exists that microspinal structure and distribution in cockroach foregut have been under at least a dual selection, for moving food posteriorly within the crop (with its concurrent mixing action) and for retaining ingested food within the crop by inhibiting regurgitation.
260
R . J . ELZINGA and T. L. HOPKINS
Acknowledgements--We thank John Krchma for S.E.M. work and Sharon Starkey for rearing and supplying most of the cockroach species used in this study (both of the Department of Entomology, Kansas State University). Thanks to Christina Nalepa, North Carolina State University, Raleigh, NC for supplying C. punctulatus. This publication is Contribution No. 93-413-J of the Kansas Agricultural Experiment Station, Kansas State University. The research was supported in part by Hatch Projects H033 and H548. REFERENCES BOUDREAUX, H. B. 1980. Proventricular acanthae and their phylogenetic implications. Ann. Entomol. Soc. Amer. 73(2): 189-96. BRACKE, J. W., D. L. CRUDEN and A. D. MARKOVETZ. 1979. Intestinal microbial flora of the American cockroach, Periplaneta americana L. Appl. Environ. Microbiol. 38: 945-55. CHAPMAN,R. F. 1985. Structure of the Digestive System, pp. 165-211. In G. A. KERKUTand L. I. GILBERT (eds.) Comprehensive Insect Physiology and Pharmacology, Vol. 4. Pergamon Press, Oxford. FisK, F. W. 1987. Order Blattodea. In F. W. STEHR (ed.) Immature Insects, Vol. I, Kendall/Hunt Publ. Co., Dubuque. Hocm, Ll, D. F., B. ROBERTS and G. D. SANSON. 1992. Anteriorly directed microspines in the foregut of Locusta migratoria (Orthoptera : Acrididae). Int. J. Insect Morphol. Embryol. 21(I): 95-7. HUBER, I. 1974. Taxonomic and ontogenetic studies of cockroaches (Blattaria). Univ. Kansas Sci. Bull. 50(6): 233-332. JUDD, W. W. 1948. A comparative study of the proventriculus of orthopteroid insects with reference to its use in taxonomy. Can. J. Res. D. 26: 93-161. McKITrR~CK, F. A. 1964. Evolutionary studies of cockroaches. Cornell Univ. Agric. Exp. Stn. Mem. 389: 1-197. MIALL, L. C. and A. DENNY. 1886. The Structure and Life History of the Cockroach (Periplaneta orientalis). Lovell Reeve Co., London. M,.LER, H. K. and F. W. FISK. 1971. Taxonomic implications of the comparative morphology of cockroach proventriculi. Ann. Entomol. Soc. Amer. 64(3): 671-87. MURALIRANGAN,M. C. and T. N. ANANTHAKRISHNAN. 1974. Taxonomic significance of the foregut armature in some Indian Acridoidea (Orthoptera). Orient. Insects 8:119--45. MURTHV, R. C. 1975. Structure of the foregut cuticle of Periplaneta americana. Experientia 32: 316-17. SNODGRASS, R. E. 1935. Principles" oflnsect Morphology. McGraw-Hill Book Co., New York.