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Specialization in the alimentary canal of some mole crickets (Orthoptera : Gryllotalpidae)
SPECIALIZATION IN THE ALIMENTARY CANAL OF SOME MOLE CRICKETS (ORTHOPTERA : GRYLLOTALPIDAE) JAMES L. NATION Department
Of
Entomology
and Nematology,
(Accepted
Univ,ersity of Florida,
7 Jamtar!
Gainesville,
FL 3261 I, U.S.A.
1983)
Abstract-The objectives of this work were to describe the structure of the gut in 4 species of mole crickets from dissections and paraffin embedded serial sections, and to use SEM techniques to study the setae-bearing papillae in the hindgut. The anatomy and histology of the guts were similar in Scapreriscus vicinus Scudder, S. acletus Rehn and Hebard, S. abbrevia/lts Scudder, and Neocurtilla hexadactyla Perty, (Orthoptera : Gryllotalpidae) but there were differences in overall length of the gut, and in the length of particular regions of the gut. The species of Scapreriscm had a female-specific gland, the proctodaeal gland, evaginated from the gut wall near the origin of the malpighian tubules. In each of the species the midgut was limited to 2 large gastric caeca. All of the gut posterior to the caeca had a cuticular lining on the cell surface and was considered to be hindgut, Thus, more than one-half of the hindgut was anterior to the origin of the malpighian tubules. The long hindgut contained clearly delineated anterior, middle, and posterior regions. The middle segment contained several rows of setae-bearing papillae projecting into the lumen of the gut. The setae trapped partially digested food and provided a suitable habitat and substrate surface for the growth of numerous microorganisms. No peritrophic membrane was found in any part of the gut. Index descriptors (in addition to those in title): Gryllotalpidae, morphology, alimentary canal, Scaprerisccts vicinus. Scapreriscrts ahhreviatrts, Neocltrtilla he.wadact.vla.
mole crickets. gut aclerus, Scaprerisms
INTRODUCTION MARTOJA (1966) has provided an excellent review of the early literature on gut anatomy in crickets. Briefly, crickets (Gryllidae) and mole crickets (Gryllotalpidae) share unusual features in gut structure not found in other groups of insects. These unusual features include a long segment of gut containing setae-bearing papillae densely-populated by microorganisms and a cuticular lining in part of the gut anterior to the malpighian tubules. The malpighian tubules do not arise from the gut directly at the junction of the mid- and hindguts as in other insects, but they empty into a common bladder connected to a ureter that leads into the hindgut. These anatomical features have caused considerable controversy over the correct terminology for the various parts of the gut, particularly the segment with a cuticular lining that is anterior to the malpighian tubules. Martoja (1966) concluded that the segment was hindgut. His arguments for hindgut hinge upon a number of points, including comparative gut structure in the Orthoptera; the view that since the malpighian tubules do not come directly off the gut they do not mark the position of the mid- and hindguts; the presence of large populations of microorganisms in the gut segment and the structure of the gut in newly hatched crickets. Yu (1982) has reported biochemical evidence that supports Martoja’s view. The specific activity of mixed function oxidases (MFO) is higher in gastric caeca tissue (midgut tissue) than it is in the 201
202
J.Artr \ I
N.X~IOP.
rest of the gut; high MFO activity is generally characteristic of midgut tissue, whereas low activity is characteristic of hindgut tissue (Yu, 1982). The papillae with their setae and microorganisms are especially interesting and have attracted the attention of several authors. Kidd (1825) seems to have been the first to call attention to the setae and papillae in the gut of a mole cricket (probably Gryllotalpa species). Ander (1939) found similar papillae and setae in all cricket subfamilies of the Gryllidae with the exception of the Myrmecophilinae. Sayce (1899) presented excellent drawings of the papillae from the gut of Gryllotalpa australis (Erichs). Martoja (1961, 1962) showed that large numbers of microorganisms lived among the setae of Gryllus bimaculaius De Geer, and he suggested that they contributed to digestion and nutrition of their host. Four species of mole crickets, Scapteriscus vicinus Scudder, S. acletus Rehn and Hebard, S. abbreviatus Scudder, and Neocurfilla hexadactyla Perty occur in Florida. The Scapteriscus species are introduced species (Walker and Nickle, 1981) that are considered economically important (Koehler and Short, 1976; Koehler, 1977; Reinert, personal communication). Analyses of the gut contents (Ulagaraj, 1975; Taylor, 1979; Matheny, 1981) led to suggestions that S. vicinus was mainly herbivorous, while S. acletus was largely carnivorous. No information exists on the internal anatomy of these 4 mole crickets, and this study was undertaken to describe the gut in them. The work also afforded an opportunity to study the setae and papillae in the hindgut with SEM techniques, and to make comparisons with published drawings and data from species of Gryllotalpa. In the divisions of the gut I followed Martoja (1966) and considered any part of the gut with a cuticular lining as either stomodaeum or proctodaeum depending upon position relative to the gastric caeca. MATERIALS
AND
METHODS
S. ricinns and S. uclertrs were collected in the Gainesville, FL, area over several years. One female of N. he.varlcrc/t’/cr was collected locally and nymphs were reared in the laboratory from eggs she laid. S. ubhrer8icrrltr was rtudjed from I alcohol preserved female that was captured in Miami. FI..
Gut tissues were fixed in aqueous Bouin’s fixative, dehydrated through a series of alcohol solutions, and paraffin. Serial sections were cut at 10 urn and stained with haematoxylin and eosin or embedded in Paraplast’ with Mallory’s triple stain (Gray, 1952). A dissecting microscope equipped with a calibrated eyepiece micrometer was used to measure internal structures in freshly dissected crickets.
Portions of the gut were dissected, heated for I5 min with 2 ml saturated KOH solution in vessels as recommended by Campbell (1929) in a glycerol bath at 16O”C, and cooled. Any remaining tissue or residue was tested for the presence of chitosan by Van Wiselingh’s chitosan color test (Campbell, 1929). Scanning Electron Microscope (SEMI The gut was dissected from freshly killed crickets in saline (9 g NaCI, 0.42 g KCI, and 0.25 g CaCI, in I L deionized water) and was subsequently transferred to 1% glutaraldehyde in 0. I M cacodylate buffer, pH 7.0 for 5 min. Some dissections were made by flooding the cricket with I% glutaraldehyde in buffered saline as the dissection was made. Tissues were passed from glutaraldehyde to water for a few minutes, and dehydrated through an alcohol series. From 100% ethanol they were transferred to hexamethyl disilarane for 5 min. air dried, mounted on stainless steel stubs, and gold coated with an Eiko 18-2 ion coater.
R E S U I. T S
The gut of S. vicinus is shown in Fig. 1, and it is representative of the structure and appearance of the gut from S. acletus, S. abbreviatus and N. hexadactyla, except that
Alimentary
Canal
-
C.C.
f
G. C.Cl.
7 -6”
Ant. Hg.
M.
.a, /r
I
203
of Some Mole Crickets
Hg.
Proc. Cl.
Post. Hg.
am
FIG. I. Alimentary canal of female Scupreriscus vicious. Malpighian tubules are not drawn to scale and are greatly reduced in number for diagrammatic simplicity. Ant. Hg. = anterior hindgut; Cr = Crop; G. C. = Gastric caeca; G. C. Cl. = Gastric caecal glands; M. Hg. = Middle hindgut: Proc. Cl. = Proctodaeal gland; Post. Hg. = Posterior hindgut.
female N. hexudactyla did not have a proctodaeal gland as did the females of the Scupteriscus species. Length of the gut and of major divisions of the gut are shown in Table 1. The total gut length, and several segments of the gut including mouth to proventriculus, proventriculus plus gastric caeca, and middle hindgut, are longer (t-test, a = 0.01) in S. TABLE
I. TOTAL
BODY LENGTH, TOTAL GUT LENGTH. AND LENGTH OF GUT SEGMENTS IN
s. vicinus (n = IO)
Measurement Total body length Total gut length Mouth to provent. Provent. and gastric Ant. hindgut Middle hindgut Post. hindgut All measurements
caeca
31.6? 50.4 18.6 5.2 4.9 13.3 8.8
” f f 2 * *
(mean + S.D.) in mm.
2.2 4.1 2.4 0.6 0.8 2.2 1.1
S. acletus (II = 10) 28.5 42.2 15.5 4.1 4.0 9.1 9.5
f + 2 -c * 2 *
1.7 4.7 2.4 0.4 0.7 1.3 0.9
4 SPECIES
S. abbreviatus (n = 1)
4.5 11 10
OF MOLE CRICKETS
N. hexadactyla (n = 1) 33 55 I7 4 5 12 13
vicinus
different
than in S. m&us. The ratio total gut length: (t-test, II = 0.01) in the 2 species.
body
length
is not significantly
The foregut
The tubular esophagus joined the crop on its lateral surface (Fig. 1). The crop was large and capable of great distension in all species. The crop of S. vicinus and S. acletus was usually empty and contained a large air bubble if the dissections were made within a day after the crickets had flown to a sound trap. Similar observations were made by Ulagaraj (1975). The crop was connected to the proventriculus by a short duct. The proventriculus contained 6 rows of heavily sclerotized teeth and a thick muscular wall that adapted it well for grinding and tearing the food. The midgut
Two large gastric caeca partially surrounded the proventriculus (Fig, 2A). The inner wall of these caeca was convoluted into deep folds that increased surface area. The tissues contained columnar cells with a brush border (Fig. 2C) and numerous nidi of regenerative cells located at the bases of the columnar cells. The lack of a cuticular lining, general cell morphology and the nidi of regenerative cells are characteristic of midgut tissue, and these caeca were, indeed, the only midgut tissue in the gut of all the mole crickets. No evidence of a peritrophic membrane, either in the gastric caeca or in any other part of the gut, was found in numerous dissections of S. vicinus and S. acletus. Attached at the base of each caecum and projecting into the hemocoel was a group of short, blind tubules (Fig. 2A,B). Their function was not determined, but they may secrete digestive enzymes and might also play a role in absorption of digested products. The hindgut
A cuticular lining that withstood hot KOH treatment and gave a positive chitosan test occurred throughout the gut posterior to the gastric caeca in each of the mole crickets. This lining was a continuous piece. from just behind the gastric caeca to the posterior termination of the gut. The hindgut began, then, just posterior to the gastric caeca. Food from the proventriculus passed directly into the anterior part of the hindgut, and was shunted past the gastric caeca by 5 long (> 3 mm) overlapping cusp-shaped proventricular valves that extended well past the opening to the gastric caeca. Only liquid food or a solution of digested products could pass between the valves. No food particles or sand grains, both of which were very common in the proventriculus and hindgut, were observed in gastric caeca. Usually little food was found in the anterior segment of the hindgut, a simple, smooth tube whose function seemed to be merely transport of food to the middle segment of hindgut. Cells in the wall of the anterior hindgut were uniform in size and had a cuticular lining on their surface (Fig. 2D). A valve controlled by a ring of circular muscle marked the junction of the anterior hindgut with the middle hindgut. This junction was clearly evident in gross dissection. The middle segment of hindgut contained 3 - 4 rows of projecting papillae with long setae along most of the length of the segment (Fig. 3A). The papillae and setae, which were in direct contact with the food because there was no peritrophic membrane, were matted with partially digested food and microorganisms. The microorganisms were both rod-shaped and filamentous. The filamentous ones were possibly actinomycetes; such as
Alimentary
Canal of Some Mole Crichets
205
FIG. 2. Scanning electron micrographs (SEM) and photomicrographs of paraffin embedded histological sections of mole cricket gut. A. SEM preparation of gastric caeca and caecal glands from S. aclefus: x 21.6; B. SEM preparation of caecal glands; x 99; C. Brush border on gastric caecal cells; x 810; D. cross-section, anterior hindgut from S. vicinus; arrow indicates chitinous lining at lumen surface; x 540.
those shown to be present in some termites (Bignell et al., 1979). A large (about 30 x 40 urn) flagellate was seen more than once, but not consistently, in the middle hindgut. Usually 1 or more nematodes were present. Ulagaraj (1975) also found these nematodes and identified them to the family Thelastomatidae. Setae on the papillae of S. vicinus and S. acletus were cleaned by an ultrasonic treatment and found to be stout, straight and to contain a cavity (Figs. 3C, D and 4A, respectively). Setae on papillae of N. hexudactyla were not as stout, but were longer and lightly curved (Fig. 3E). Details of the setae in S. abbreviutus (Fig. 3B) could not be determined from the 1 individual available. Although the setae were slightly deformed by hot KOH treatment, they survived (Fig. 3F), and clearly their composition is largely, if not entirely, chitinous.
206
FIG. 3. SEM preparations of papillae and setae from middle hindgut of mole crickets. A. Cleaned from papillae and setae from S. vicinus. x 108; B. Setae matted with food and microorganisms middle hindgut of S. abbreviatus, x 567; C. cleaned setae from S. vicious, x 1080; D. cleaned setae from S. oclelus, x 657; E. setae matted with food and microorganisms from N. hexuducfylu, x 990 F. setae from S. vicinus after hot KOH treatment, x 261.
Alimentary
Canal
of Some Mole Crickets
207
A large cluster of malpighian tubules wrapped around the midpoint of the middle hindgut segment. The tubules did not arise, however, from the gut directly as in other groups of insects, but had their origin from a common bladder (Fig. 4B) attached to a ureter that emptied into the hindgut at the junction of the middle and posterior segments. In S. vicinus and S. acletus there were 3 types of tubules (Fig. 4C). In dissections the tubules could easily be classed as yellow, white, or having small (50 x 70 urn) white nodules of uric acid, but the types observable from dissections were not identified with the histological types. One of the 3 types had a brush border on the lumen surface (Fig. 4D). Females of the Scupteriscus species had a gland that was never present in males at the junction between the middle and posterior segments of hindgut. I propose the name proctodaeal gland for this structure, which earlier workers failed to find in Gryllotalpa species, and which may be restricted to and characteristic of the genus Scapteriscus. The lumen of the gland usually contained black fluid, but no food particles. The cuticular lining was slightly wrinkled, but it bore no setae. The gland was present in nymphal females, and it enlarged as the ovaries matured and as eggs developed in the ovaries (Table 2). Although the function of the gland was not determined, its enlargement with sexual maturity suggests that it might have some reproductive function.
FIN. 4. A. SEM preparation of setae from S. vicinus after cleaning and shearing of some setae by prolonged ultrasonic treatment to show that setae are hollow, x 4410; B. paraffin embedded crosssection of malpighian tubules and bladder from S. aclefus; x 25.2; C. Cross-section of malpighian tubules, S. acletus; x 90. Note 3 types of tubules based on cell morphology and diameter of tubule lumen; D. malpighian tubule from S. aclefus with thick wall and brush border on lumen surface; x
s. vicin1rs * oocyte Month
Oct. No\. DW. Jan. Feb. Mar.
II
0 I 6 4 0 5
S. aclelusi
length
proctodaeal length
gland width
oocyte length
proctodaeal length
gland width
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
1.oo 1.02 I .O3
1.10 I .23 1.08
1.00 1.30 I .28
1.26
I .30
0.64 0.81 0.86 0.86 I .05 1.10
0.58 0.93 O.UR
0.98
0.78 0.91 0.91 1.42 1.oo 0.90
1.oo 1.00 1.00
*S. vicin~~ individuals were dissected for measurements as they were sound-trapped. Eggs deposited in laboratory soil cultures measured I .8 x 3.2 mm (n = 41). tAll S. aclerus were sound-trapped in Oct. 1978 and were then held individually in containers of roil with dog food until dissected. Eggs deposited in laboratory soil cultures measured 1.8 x 3.0 mm (n = 25).
I) I S c‘ U S S I 0 N
The gut is morphologically similar in each of the 4 species of mole crickets. One notable difference among the crickets is the presence of the proctodaeal gland in females of Scupreriscus species and its absence in females of N. hexadactylu. The earlier suggestions and gut analyses indicating a preference for plant food by S. vicinus are supported by the structure of the gut. The gut is longer in S. vicinus than in S. aclefus, and specifically, the middle hindgut segment is longer in S. vicinus. This segment is probably where most of the chemical digestion occurs, and its longer length reflects the greater difficulty of digesting plant cell walls. Feeding patterns in S. abbreviatus and in N. hexuducfylu have not been determined, but the middle and posterior segments of the hindgut are relatively long in these 2 crickets, and it is likely that they are predominantly plant eaters. No food was found in the gastric caeca, but these organs are rich sources of protease, amylase, and lipase (unpublished data). The middle hindgut may also be a major site of absorption of digested materials. The cuticular lining on the cells need not indicate inability to absorb small molecules. Absorption of several substances, including sugars and amino acids, occurs in the hindgut of some insects (Wall and Oschman, 1970), and has been suggested in others (Bayon, 1971; Bignell et al., 1980). The rich populations of microorganisms in the middle hindgut probably contribute to nutrition of crickets through synthesis of new proteins, vitamins, and sterols that can be utilized by the crickets. One function of the setae on the papillae may be to trap food coming through the gut, and to provide a suitable substrate surface for the growth of the microorganisms. Similar setae and high populations of microorganisms have recently been described from 1979, 1980) and from a beetle larva, Oryctes the hindgut of termites (Bignell et al., nasicornis L. (Bayon, 1971). The cuticular lining in the hindgut and the setae on the papillae are molted. The old cuticular lining is shed into the lumen of the gut. Papillae and setae of newly molted crickets are nearly free of food and microorganisms. Presumably crickets rapidly become reinfected, and small numbers of microorganisms remaining in the gut may multiply rapidly. Martoja (1966) identified 5 species of microorganisms from the gut of Cry//us bimaculatus L., but no additional studies of the microorganisms have been published.
Alimentary
Canal
of Some Mole Crickets
209
Probably more species remain to be identified, as well as their relationship to the crickets. Each species of cricket may have its own characteristic collection of microorganisms. This seems like a rich field worthy of investigation. Paired anal glands are not part of the gut, but some earlier workers (e.g. Sayce, 1899) suggested that they opened into the hindgut at the rectum. Careful dissection and staining of the glands showed that they actually opened to the exterior at each side of the anal opening. The glands were 2 - 3-mm long in S. vicinus and S. acletus and about 4-mm long in N. hexadactyla. These glands contained a fluid that gelled upon exposure to the air and became sticky and mucilaginous. Mole crickets frequently eject fluid from these glands and defecate when handled, probably as defensive reactions. The sticky anal gland secretion might entangle small predators, such as ants; it may also contain substances that are distasteful or irritating. It is not, however, the source of the offensive odor associated with agitated mole crickets. Glands were carefully dissected from S. vicinus and S. aclefus and crushed on a laboratory tissue. No odor was detectable. The crushed rectum, however, produced the characteristic, foul odor. Clearly this odor comes from the gut itself, probably from the rectum.
Acknowledgemenfs-I thank Dr. T. J. Walker for collection of some of the crickets and for numerous discussions of cricket morphology and biology, Ms. Pat Carlysle, USDA, Gainesville, for initial introduction to SEM techniques, Dr. Greg Erdos, Univ. of Florida, for help with SEM procedures and use of the microscope, Dr. Harvey Cromroy, Univ. of Florida, and Dr. Don Jouvenez, USDA, Gainesville, for assistance with photography through the microscope and Ms. Kathy Dennis who made many dissections and rendered able technical assistance. I thank Drs. Tom Walker, Simon Yu and 2 anonymous reviewers for critical reading of the manuscript, and Mrs. Glinda Benson for typing the manuscript.
REFERENCES K. 1939. Vergleichend anatomische und phylogenetische Studien iiber die Ensifera (Saltatoria). Opus. Entomol. (Suppl.) 2: I ~ 306. BAYON, C. 1971. La cuticule proctodeal de la larve d’Orvc/es ncrsicornrs L. (ColPopteres ScarabPides). Etude au microscope electronique a balayage. J. Microsc. (Paris) I I: 353 - 70. BIC~NELI., D. E., H. OSKARSSON and J. M. ANDERSON. 1979. Association of actinomycete-like bacteria with soil-feeding termites (Termitidae, Termitinae). Appl. Environ. Microbial. 37: 339-42. BIGNELL, D. E., H. OSKARSSON and J. M. ANDERSON. 1980. Specialization of the hindgut wall for the attachment of symbiotic micro-organisms in a termite Procubitermes aburiensis (Isoptera, Termitidae, Termitinae). Zoomorphologie 96: 103 ~ 12. CAMPBELI , F. L. 1929. The detection and estimation of insect chitin; and the irrelation of chitinization to hardness and pigmentation of the cuticle of the American cockroach, Periplaneta americana L. ANDEK,
Ann. Entomol. Sot. Amer. 22: 401 - 26. GRAY, P. 1952. Handbook of Basic Microtechnique.
The Blakiston Co. New York. KIDD, J. 1825. On the anatomy of the mole-cricket. Phi/ox Trans. R. Sot. Land. 115: 205 -46. KOEHL.ER, P. G. 1977. Biology and control of mole crickets in pasture. Florida Coop. Ext. Serv. Publ. No. ENY-28. KO~HLER, P. G. and D. E. SHORT. 1976. Control of mole crickets in pasturegrass. J. Econ. Entomol. 69: 229 - 32.
MAKTO.I.\. R. 1961. Signification anatomique et biologique du regment B villosltCc de I’intestin de\ Grylloidea (Orthopteres). C. R. Acad. Ser. Paris 2531): 2759 - 61, M.\KTOI.I. R. 1962. Assimilation de la cellulose et microorganisme5 intestinaux chew Cry//us brmuculuruc De Geer (Insecte, Orthopttre, Grylioidea). C. K. Acad. Sci. furis 2541): 3040 42. MARTOJA, R. 1966. Sur quelques aspects de la biologie des orthopteres en relation avec la presence de concentrations microaiennes (bactkries intestinals, rickettsies). Ann. Sot. Entomol. Fr. 2: 753 - 940. MATHENY, E. L., JR. 1981. Contrasting feeding habits of pest mole cricket species. J. Econ. Entomol. 74: 444-45.
210
JAMES L. NATION
1899. On the structure of the alimentary system of Gry//ofa/pa ausrrdis (Erichs.) with some physiological notes. Proc. R. Sot. Victoria 11: 114- 29. TAYLOR, T. R. 1979. Crop contents of two species of mole crickets, Scapteriscus aclelus and S. vicinus (Orthoptera : Gryllotalpidae). F/u. Entomo/. 62: 278 - 79. ULAGARAJ, S. M. 1975. Food habits of mole crickets (Orthoptera : Gryllotalpidae : Scupreriscus). J. Cu. Entomol. Sot. 10: 229 - 3 1. WALKER, T. J. and D. A. NICKLE. 1981. Introduction and spread of pest mole crickets: Scupleriscus vicinus and S. acleius re-examined. Ann. Enromol. Sec. Amer. 74: I58 - 63. WAL I, B. J. and J. L. OSCHMAN, 1970. Water and solute uptake by the rectal pads of Peripluneta amerrcunu. Amer. J. Physiol. 218: 1208 ~ 15. Yu, S. J. 1982. Microsomal oxidases in the mole crickets, Scupteriscus acletus Rehn and Hebard and Scupreriscus vicinus Scudder. Pest. Biochem. Physiol. 17: 170- 76.
SAYCE, 0. A.
Of
Entomology
and Nematology,
(Accepted
Univ,ersity of Florida,
7 Jamtar!
Gainesville,
FL 3261 I, U.S.A.
1983)
Abstract-The objectives of this work were to describe the structure of the gut in 4 species of mole crickets from dissections and paraffin embedded serial sections, and to use SEM techniques to study the setae-bearing papillae in the hindgut. The anatomy and histology of the guts were similar in Scapreriscus vicinus Scudder, S. acletus Rehn and Hebard, S. abbrevia/lts Scudder, and Neocurtilla hexadactyla Perty, (Orthoptera : Gryllotalpidae) but there were differences in overall length of the gut, and in the length of particular regions of the gut. The species of Scapreriscm had a female-specific gland, the proctodaeal gland, evaginated from the gut wall near the origin of the malpighian tubules. In each of the species the midgut was limited to 2 large gastric caeca. All of the gut posterior to the caeca had a cuticular lining on the cell surface and was considered to be hindgut, Thus, more than one-half of the hindgut was anterior to the origin of the malpighian tubules. The long hindgut contained clearly delineated anterior, middle, and posterior regions. The middle segment contained several rows of setae-bearing papillae projecting into the lumen of the gut. The setae trapped partially digested food and provided a suitable habitat and substrate surface for the growth of numerous microorganisms. No peritrophic membrane was found in any part of the gut. Index descriptors (in addition to those in title): Gryllotalpidae, morphology, alimentary canal, Scaprerisccts vicinus. Scapreriscrts ahhreviatrts, Neocltrtilla he.wadact.vla.
mole crickets. gut aclerus, Scaprerisms
INTRODUCTION MARTOJA (1966) has provided an excellent review of the early literature on gut anatomy in crickets. Briefly, crickets (Gryllidae) and mole crickets (Gryllotalpidae) share unusual features in gut structure not found in other groups of insects. These unusual features include a long segment of gut containing setae-bearing papillae densely-populated by microorganisms and a cuticular lining in part of the gut anterior to the malpighian tubules. The malpighian tubules do not arise from the gut directly at the junction of the mid- and hindguts as in other insects, but they empty into a common bladder connected to a ureter that leads into the hindgut. These anatomical features have caused considerable controversy over the correct terminology for the various parts of the gut, particularly the segment with a cuticular lining that is anterior to the malpighian tubules. Martoja (1966) concluded that the segment was hindgut. His arguments for hindgut hinge upon a number of points, including comparative gut structure in the Orthoptera; the view that since the malpighian tubules do not come directly off the gut they do not mark the position of the mid- and hindguts; the presence of large populations of microorganisms in the gut segment and the structure of the gut in newly hatched crickets. Yu (1982) has reported biochemical evidence that supports Martoja’s view. The specific activity of mixed function oxidases (MFO) is higher in gastric caeca tissue (midgut tissue) than it is in the 201
202
J.Artr \ I
N.X~IOP.
rest of the gut; high MFO activity is generally characteristic of midgut tissue, whereas low activity is characteristic of hindgut tissue (Yu, 1982). The papillae with their setae and microorganisms are especially interesting and have attracted the attention of several authors. Kidd (1825) seems to have been the first to call attention to the setae and papillae in the gut of a mole cricket (probably Gryllotalpa species). Ander (1939) found similar papillae and setae in all cricket subfamilies of the Gryllidae with the exception of the Myrmecophilinae. Sayce (1899) presented excellent drawings of the papillae from the gut of Gryllotalpa australis (Erichs). Martoja (1961, 1962) showed that large numbers of microorganisms lived among the setae of Gryllus bimaculaius De Geer, and he suggested that they contributed to digestion and nutrition of their host. Four species of mole crickets, Scapteriscus vicinus Scudder, S. acletus Rehn and Hebard, S. abbreviatus Scudder, and Neocurfilla hexadactyla Perty occur in Florida. The Scapteriscus species are introduced species (Walker and Nickle, 1981) that are considered economically important (Koehler and Short, 1976; Koehler, 1977; Reinert, personal communication). Analyses of the gut contents (Ulagaraj, 1975; Taylor, 1979; Matheny, 1981) led to suggestions that S. vicinus was mainly herbivorous, while S. acletus was largely carnivorous. No information exists on the internal anatomy of these 4 mole crickets, and this study was undertaken to describe the gut in them. The work also afforded an opportunity to study the setae and papillae in the hindgut with SEM techniques, and to make comparisons with published drawings and data from species of Gryllotalpa. In the divisions of the gut I followed Martoja (1966) and considered any part of the gut with a cuticular lining as either stomodaeum or proctodaeum depending upon position relative to the gastric caeca. MATERIALS
AND
METHODS
S. ricinns and S. uclertrs were collected in the Gainesville, FL, area over several years. One female of N. he.varlcrc/t’/cr was collected locally and nymphs were reared in the laboratory from eggs she laid. S. ubhrer8icrrltr was rtudjed from I alcohol preserved female that was captured in Miami. FI..
Gut tissues were fixed in aqueous Bouin’s fixative, dehydrated through a series of alcohol solutions, and paraffin. Serial sections were cut at 10 urn and stained with haematoxylin and eosin or embedded in Paraplast’ with Mallory’s triple stain (Gray, 1952). A dissecting microscope equipped with a calibrated eyepiece micrometer was used to measure internal structures in freshly dissected crickets.
Portions of the gut were dissected, heated for I5 min with 2 ml saturated KOH solution in vessels as recommended by Campbell (1929) in a glycerol bath at 16O”C, and cooled. Any remaining tissue or residue was tested for the presence of chitosan by Van Wiselingh’s chitosan color test (Campbell, 1929). Scanning Electron Microscope (SEMI The gut was dissected from freshly killed crickets in saline (9 g NaCI, 0.42 g KCI, and 0.25 g CaCI, in I L deionized water) and was subsequently transferred to 1% glutaraldehyde in 0. I M cacodylate buffer, pH 7.0 for 5 min. Some dissections were made by flooding the cricket with I% glutaraldehyde in buffered saline as the dissection was made. Tissues were passed from glutaraldehyde to water for a few minutes, and dehydrated through an alcohol series. From 100% ethanol they were transferred to hexamethyl disilarane for 5 min. air dried, mounted on stainless steel stubs, and gold coated with an Eiko 18-2 ion coater.
R E S U I. T S
The gut of S. vicinus is shown in Fig. 1, and it is representative of the structure and appearance of the gut from S. acletus, S. abbreviatus and N. hexadactyla, except that
Alimentary
Canal
-
C.C.
f
G. C.Cl.
7 -6”
Ant. Hg.
M.
.a, /r
I
203
of Some Mole Crickets
Hg.
Proc. Cl.
Post. Hg.
am
FIG. I. Alimentary canal of female Scupreriscus vicious. Malpighian tubules are not drawn to scale and are greatly reduced in number for diagrammatic simplicity. Ant. Hg. = anterior hindgut; Cr = Crop; G. C. = Gastric caeca; G. C. Cl. = Gastric caecal glands; M. Hg. = Middle hindgut: Proc. Cl. = Proctodaeal gland; Post. Hg. = Posterior hindgut.
female N. hexudactyla did not have a proctodaeal gland as did the females of the Scupteriscus species. Length of the gut and of major divisions of the gut are shown in Table 1. The total gut length, and several segments of the gut including mouth to proventriculus, proventriculus plus gastric caeca, and middle hindgut, are longer (t-test, a = 0.01) in S. TABLE
I. TOTAL
BODY LENGTH, TOTAL GUT LENGTH. AND LENGTH OF GUT SEGMENTS IN
s. vicinus (n = IO)
Measurement Total body length Total gut length Mouth to provent. Provent. and gastric Ant. hindgut Middle hindgut Post. hindgut All measurements
caeca
31.6? 50.4 18.6 5.2 4.9 13.3 8.8
” f f 2 * *
(mean + S.D.) in mm.
2.2 4.1 2.4 0.6 0.8 2.2 1.1
S. acletus (II = 10) 28.5 42.2 15.5 4.1 4.0 9.1 9.5
f + 2 -c * 2 *
1.7 4.7 2.4 0.4 0.7 1.3 0.9
4 SPECIES
S. abbreviatus (n = 1)
4.5 11 10
OF MOLE CRICKETS
N. hexadactyla (n = 1) 33 55 I7 4 5 12 13
vicinus
different
than in S. m&us. The ratio total gut length: (t-test, II = 0.01) in the 2 species.
body
length
is not significantly
The foregut
The tubular esophagus joined the crop on its lateral surface (Fig. 1). The crop was large and capable of great distension in all species. The crop of S. vicinus and S. acletus was usually empty and contained a large air bubble if the dissections were made within a day after the crickets had flown to a sound trap. Similar observations were made by Ulagaraj (1975). The crop was connected to the proventriculus by a short duct. The proventriculus contained 6 rows of heavily sclerotized teeth and a thick muscular wall that adapted it well for grinding and tearing the food. The midgut
Two large gastric caeca partially surrounded the proventriculus (Fig, 2A). The inner wall of these caeca was convoluted into deep folds that increased surface area. The tissues contained columnar cells with a brush border (Fig. 2C) and numerous nidi of regenerative cells located at the bases of the columnar cells. The lack of a cuticular lining, general cell morphology and the nidi of regenerative cells are characteristic of midgut tissue, and these caeca were, indeed, the only midgut tissue in the gut of all the mole crickets. No evidence of a peritrophic membrane, either in the gastric caeca or in any other part of the gut, was found in numerous dissections of S. vicinus and S. acletus. Attached at the base of each caecum and projecting into the hemocoel was a group of short, blind tubules (Fig. 2A,B). Their function was not determined, but they may secrete digestive enzymes and might also play a role in absorption of digested products. The hindgut
A cuticular lining that withstood hot KOH treatment and gave a positive chitosan test occurred throughout the gut posterior to the gastric caeca in each of the mole crickets. This lining was a continuous piece. from just behind the gastric caeca to the posterior termination of the gut. The hindgut began, then, just posterior to the gastric caeca. Food from the proventriculus passed directly into the anterior part of the hindgut, and was shunted past the gastric caeca by 5 long (> 3 mm) overlapping cusp-shaped proventricular valves that extended well past the opening to the gastric caeca. Only liquid food or a solution of digested products could pass between the valves. No food particles or sand grains, both of which were very common in the proventriculus and hindgut, were observed in gastric caeca. Usually little food was found in the anterior segment of the hindgut, a simple, smooth tube whose function seemed to be merely transport of food to the middle segment of hindgut. Cells in the wall of the anterior hindgut were uniform in size and had a cuticular lining on their surface (Fig. 2D). A valve controlled by a ring of circular muscle marked the junction of the anterior hindgut with the middle hindgut. This junction was clearly evident in gross dissection. The middle segment of hindgut contained 3 - 4 rows of projecting papillae with long setae along most of the length of the segment (Fig. 3A). The papillae and setae, which were in direct contact with the food because there was no peritrophic membrane, were matted with partially digested food and microorganisms. The microorganisms were both rod-shaped and filamentous. The filamentous ones were possibly actinomycetes; such as
Alimentary
Canal of Some Mole Crichets
205
FIG. 2. Scanning electron micrographs (SEM) and photomicrographs of paraffin embedded histological sections of mole cricket gut. A. SEM preparation of gastric caeca and caecal glands from S. aclefus: x 21.6; B. SEM preparation of caecal glands; x 99; C. Brush border on gastric caecal cells; x 810; D. cross-section, anterior hindgut from S. vicinus; arrow indicates chitinous lining at lumen surface; x 540.
those shown to be present in some termites (Bignell et al., 1979). A large (about 30 x 40 urn) flagellate was seen more than once, but not consistently, in the middle hindgut. Usually 1 or more nematodes were present. Ulagaraj (1975) also found these nematodes and identified them to the family Thelastomatidae. Setae on the papillae of S. vicinus and S. acletus were cleaned by an ultrasonic treatment and found to be stout, straight and to contain a cavity (Figs. 3C, D and 4A, respectively). Setae on papillae of N. hexudactyla were not as stout, but were longer and lightly curved (Fig. 3E). Details of the setae in S. abbreviutus (Fig. 3B) could not be determined from the 1 individual available. Although the setae were slightly deformed by hot KOH treatment, they survived (Fig. 3F), and clearly their composition is largely, if not entirely, chitinous.
206
FIG. 3. SEM preparations of papillae and setae from middle hindgut of mole crickets. A. Cleaned from papillae and setae from S. vicinus. x 108; B. Setae matted with food and microorganisms middle hindgut of S. abbreviatus, x 567; C. cleaned setae from S. vicious, x 1080; D. cleaned setae from S. oclelus, x 657; E. setae matted with food and microorganisms from N. hexuducfylu, x 990 F. setae from S. vicinus after hot KOH treatment, x 261.
Alimentary
Canal
of Some Mole Crickets
207
A large cluster of malpighian tubules wrapped around the midpoint of the middle hindgut segment. The tubules did not arise, however, from the gut directly as in other groups of insects, but had their origin from a common bladder (Fig. 4B) attached to a ureter that emptied into the hindgut at the junction of the middle and posterior segments. In S. vicinus and S. acletus there were 3 types of tubules (Fig. 4C). In dissections the tubules could easily be classed as yellow, white, or having small (50 x 70 urn) white nodules of uric acid, but the types observable from dissections were not identified with the histological types. One of the 3 types had a brush border on the lumen surface (Fig. 4D). Females of the Scupteriscus species had a gland that was never present in males at the junction between the middle and posterior segments of hindgut. I propose the name proctodaeal gland for this structure, which earlier workers failed to find in Gryllotalpa species, and which may be restricted to and characteristic of the genus Scapteriscus. The lumen of the gland usually contained black fluid, but no food particles. The cuticular lining was slightly wrinkled, but it bore no setae. The gland was present in nymphal females, and it enlarged as the ovaries matured and as eggs developed in the ovaries (Table 2). Although the function of the gland was not determined, its enlargement with sexual maturity suggests that it might have some reproductive function.
FIN. 4. A. SEM preparation of setae from S. vicinus after cleaning and shearing of some setae by prolonged ultrasonic treatment to show that setae are hollow, x 4410; B. paraffin embedded crosssection of malpighian tubules and bladder from S. aclefus; x 25.2; C. Cross-section of malpighian tubules, S. acletus; x 90. Note 3 types of tubules based on cell morphology and diameter of tubule lumen; D. malpighian tubule from S. aclefus with thick wall and brush border on lumen surface; x
s. vicin1rs * oocyte Month
Oct. No\. DW. Jan. Feb. Mar.
II
0 I 6 4 0 5
S. aclelusi
length
proctodaeal length
gland width
oocyte length
proctodaeal length
gland width
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
1.oo 1.02 I .O3
1.10 I .23 1.08
1.00 1.30 I .28
1.26
I .30
0.64 0.81 0.86 0.86 I .05 1.10
0.58 0.93 O.UR
0.98
0.78 0.91 0.91 1.42 1.oo 0.90
1.oo 1.00 1.00
*S. vicin~~ individuals were dissected for measurements as they were sound-trapped. Eggs deposited in laboratory soil cultures measured I .8 x 3.2 mm (n = 41). tAll S. aclerus were sound-trapped in Oct. 1978 and were then held individually in containers of roil with dog food until dissected. Eggs deposited in laboratory soil cultures measured 1.8 x 3.0 mm (n = 25).
I) I S c‘ U S S I 0 N
The gut is morphologically similar in each of the 4 species of mole crickets. One notable difference among the crickets is the presence of the proctodaeal gland in females of Scupreriscus species and its absence in females of N. hexadactylu. The earlier suggestions and gut analyses indicating a preference for plant food by S. vicinus are supported by the structure of the gut. The gut is longer in S. vicinus than in S. aclefus, and specifically, the middle hindgut segment is longer in S. vicinus. This segment is probably where most of the chemical digestion occurs, and its longer length reflects the greater difficulty of digesting plant cell walls. Feeding patterns in S. abbreviatus and in N. hexuducfylu have not been determined, but the middle and posterior segments of the hindgut are relatively long in these 2 crickets, and it is likely that they are predominantly plant eaters. No food was found in the gastric caeca, but these organs are rich sources of protease, amylase, and lipase (unpublished data). The middle hindgut may also be a major site of absorption of digested materials. The cuticular lining on the cells need not indicate inability to absorb small molecules. Absorption of several substances, including sugars and amino acids, occurs in the hindgut of some insects (Wall and Oschman, 1970), and has been suggested in others (Bayon, 1971; Bignell et al., 1980). The rich populations of microorganisms in the middle hindgut probably contribute to nutrition of crickets through synthesis of new proteins, vitamins, and sterols that can be utilized by the crickets. One function of the setae on the papillae may be to trap food coming through the gut, and to provide a suitable substrate surface for the growth of the microorganisms. Similar setae and high populations of microorganisms have recently been described from 1979, 1980) and from a beetle larva, Oryctes the hindgut of termites (Bignell et al., nasicornis L. (Bayon, 1971). The cuticular lining in the hindgut and the setae on the papillae are molted. The old cuticular lining is shed into the lumen of the gut. Papillae and setae of newly molted crickets are nearly free of food and microorganisms. Presumably crickets rapidly become reinfected, and small numbers of microorganisms remaining in the gut may multiply rapidly. Martoja (1966) identified 5 species of microorganisms from the gut of Cry//us bimaculatus L., but no additional studies of the microorganisms have been published.
Alimentary
Canal
of Some Mole Crickets
209
Probably more species remain to be identified, as well as their relationship to the crickets. Each species of cricket may have its own characteristic collection of microorganisms. This seems like a rich field worthy of investigation. Paired anal glands are not part of the gut, but some earlier workers (e.g. Sayce, 1899) suggested that they opened into the hindgut at the rectum. Careful dissection and staining of the glands showed that they actually opened to the exterior at each side of the anal opening. The glands were 2 - 3-mm long in S. vicinus and S. acletus and about 4-mm long in N. hexadactyla. These glands contained a fluid that gelled upon exposure to the air and became sticky and mucilaginous. Mole crickets frequently eject fluid from these glands and defecate when handled, probably as defensive reactions. The sticky anal gland secretion might entangle small predators, such as ants; it may also contain substances that are distasteful or irritating. It is not, however, the source of the offensive odor associated with agitated mole crickets. Glands were carefully dissected from S. vicinus and S. aclefus and crushed on a laboratory tissue. No odor was detectable. The crushed rectum, however, produced the characteristic, foul odor. Clearly this odor comes from the gut itself, probably from the rectum.
Acknowledgemenfs-I thank Dr. T. J. Walker for collection of some of the crickets and for numerous discussions of cricket morphology and biology, Ms. Pat Carlysle, USDA, Gainesville, for initial introduction to SEM techniques, Dr. Greg Erdos, Univ. of Florida, for help with SEM procedures and use of the microscope, Dr. Harvey Cromroy, Univ. of Florida, and Dr. Don Jouvenez, USDA, Gainesville, for assistance with photography through the microscope and Ms. Kathy Dennis who made many dissections and rendered able technical assistance. I thank Drs. Tom Walker, Simon Yu and 2 anonymous reviewers for critical reading of the manuscript, and Mrs. Glinda Benson for typing the manuscript.
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Ann. Entomol. Sot. Amer. 22: 401 - 26. GRAY, P. 1952. Handbook of Basic Microtechnique.
The Blakiston Co. New York. KIDD, J. 1825. On the anatomy of the mole-cricket. Phi/ox Trans. R. Sot. Land. 115: 205 -46. KOEHL.ER, P. G. 1977. Biology and control of mole crickets in pasture. Florida Coop. Ext. Serv. Publ. No. ENY-28. KO~HLER, P. G. and D. E. SHORT. 1976. Control of mole crickets in pasturegrass. J. Econ. Entomol. 69: 229 - 32.
MAKTO.I.\. R. 1961. Signification anatomique et biologique du regment B villosltCc de I’intestin de\ Grylloidea (Orthopteres). C. R. Acad. Ser. Paris 2531): 2759 - 61, M.\KTOI.I. R. 1962. Assimilation de la cellulose et microorganisme5 intestinaux chew Cry//us brmuculuruc De Geer (Insecte, Orthopttre, Grylioidea). C. K. Acad. Sci. furis 2541): 3040 42. MARTOJA, R. 1966. Sur quelques aspects de la biologie des orthopteres en relation avec la presence de concentrations microaiennes (bactkries intestinals, rickettsies). Ann. Sot. Entomol. Fr. 2: 753 - 940. MATHENY, E. L., JR. 1981. Contrasting feeding habits of pest mole cricket species. J. Econ. Entomol. 74: 444-45.
210
JAMES L. NATION
1899. On the structure of the alimentary system of Gry//ofa/pa ausrrdis (Erichs.) with some physiological notes. Proc. R. Sot. Victoria 11: 114- 29. TAYLOR, T. R. 1979. Crop contents of two species of mole crickets, Scapteriscus aclelus and S. vicinus (Orthoptera : Gryllotalpidae). F/u. Entomo/. 62: 278 - 79. ULAGARAJ, S. M. 1975. Food habits of mole crickets (Orthoptera : Gryllotalpidae : Scupreriscus). J. Cu. Entomol. Sot. 10: 229 - 3 1. WALKER, T. J. and D. A. NICKLE. 1981. Introduction and spread of pest mole crickets: Scupleriscus vicinus and S. acleius re-examined. Ann. Enromol. Sec. Amer. 74: I58 - 63. WAL I, B. J. and J. L. OSCHMAN, 1970. Water and solute uptake by the rectal pads of Peripluneta amerrcunu. Amer. J. Physiol. 218: 1208 ~ 15. Yu, S. J. 1982. Microsomal oxidases in the mole crickets, Scupteriscus acletus Rehn and Hebard and Scupreriscus vicinus Scudder. Pest. Biochem. Physiol. 17: 170- 76.
SAYCE, 0. A.