Conspecifics as Food Sources

The remaining cases of animal-based food pertain to fellow cockroaches. This fits the profile of other detritivores, as intraguild predation and cannibalism are widespread within decomposer food webs (Scheu and Setala, 2002). There are a few cases of cockroaches preying on other cockroach species, like N. cinerea killing and eating D. punctata (Roth, 2003a). A more significant source of animal tissue, however, originates from same-species interactions (Nalepa, 1994). Most records of cockroach cannibalism come from domestic pests in lab culture (e.g., Periplaneta spp.—Pope, 1953; Roth, 1981a; B. german-ica—Gordon, 1959),and it is the vulnerable that are most often taken as prey. Hatchlings, freshly molted nymphs, and the weak or wounded are the most frequent victims. It is usually the abdomen that is eaten first, to take advantage of the uric acid pool stored in the fat body (Cochran, 1985). Adult cockroaches in culture (Abbott, 1926) and in caves (Darlington, 1970) often have their wings extensively nibbled (although this may also be the result of aggressive interactions). The most ubiquitous ecological factor favoring cannibalism is the quality and quantity of available food, which depends to varying degrees upon population density (Elgar and Crespi, 1992).

Egg eating is a form of cannibalism, although in some cases the ingested eggs may be unfertilized or unviable (Joyner and Gould, 1986). In cockroaches, oothecae may be partially or entirely eaten prior to hatch (Roth and Willis, 1954b;Nalepa, 1988a),and oothecae carried by fe

Costa Rican Flying Cockroach
Fig. 4.6 The Costa Rican cockroach Macrophyllodromia maximiliani palpating the elytron of the fulgorid Copidocephala guttata. From Roth and Naskrecki (2001), courtesy of Piotr Naskrecki, with permission from the Journal of Orthoptera Research.

Table 4.5. Organic composition of exuvia from adult ecdysis and oothecae from several cockroach species, as determined by 13C-NMR analyses. Reprinted from Kramer et al., "Analysis of cockroach oothecae and exuvia by solid state 13C-NMR spectroscopy," Insect Biochemistry 21 (1991): pp. 14956; copyright (1991), with permission from Elsevier.

Table 4.5. Organic composition of exuvia from adult ecdysis and oothecae from several cockroach species, as determined by 13C-NMR analyses. Reprinted from Kramer et al., "Analysis of cockroach oothecae and exuvia by solid state 13C-NMR spectroscopy," Insect Biochemistry 21 (1991): pp. 14956; copyright (1991), with permission from Elsevier.

Relative amount (%) in/on exuvia

Species

Protein

Chitin

Diphenol

Lipid

Periplaneta americana

49

38

11

2

Blattella germanica

59

30

9

2

Gromphadorhina portentosa

53

38

8

1

Blaberus craniifer

52

42

5

1

Rhyparobia maderae

61

35

4

1

Relative amount (%) in/on post-hatch oothecae

Species

Protein

Oxalate

Diphenol

Lipid

Periplaneta americana

87

8

4

1

Periplaneta fuliginosa

86

7

6

1

Blatta orientalis

88

7

4

1

Blattella germanica

95

< 1

3

1

males are not immune to biting and cannibalism by con-specifics (Roth and Willis, 1954b; Willis et al., 1958). After hatch, neonates of ovoviviparous cockroaches eat the embryonic membranes and the oothecal case (Nutting, 1953b; Willis et al., 1958); the sturdier oothecal cases of oviparous species are probably eaten by older nymphs or adults. After hatch in Cryptocercus, for example, oothecal cases are occasionally found still embedded in wood, but chewed flush with the surface of the gallery; hatching oothecae isolated from adults always remain intact (Na-lepa and Mullins, 1992). It is estimated that females of Cryptocercus may be able to recover up to 59% of the nitrogen invested into a clutch of eggs by consuming the oothecal cases after hatch, but it is unknown how much of this nitrogen is assimilated (Nalepa and Mullins, 1992). Cannibalism may be part of an evolved life history strategy in young families of Cryptocercus (Nalepa and Bell, 1997; Chapter 8).

Cast skins are a prized food source and are eaten quickly by the newly molted nymph or by nearby individuals. In P. americana the cast skin is usually consumed within an hour after molt (Gould and Deay, 1938), and the older the nymph, the more quickly the skin is eaten (Nigam, 1932). Nymphs of B. germanica are known to force newly emerged individuals away from their cast skins and "commence to eat the latter with great gusto" (Ross, 1929). A nymph of E. posticus usually eats its exu-vium immediately after molt, before the new cuticle has hardened. Nearby cockroaches also eat fresh exuvia, and occasionally the molting cockroach as well (Darlington, 1970). Competition to feed on exuvia has been observed in both Macropanesthia (M. Slaytor, pers. comm. to CAN) and Cryptocercus (CAN, unpubl. obs.). In the latter, "snatch and run" bouts can occur where an exuvium changes ownership a half dozen times or more before it is completely consumed. The competition is understandable in that a cast skin is a considerable investment on the part of a growing nymph; exuvia from young instars of E. posticus, for example, comprise nearly 16% of their dry weight (Darlington, 1970). The cuticle is made up of chains of a polysaccharide, chitin, embedded in a protein matrix. Protein and chitin are 17% and 7% nitrogen by mass, respectively (Chown and Nicolson, 2004), and together these may account for 95% or more of the organic materials in an exuvium or oothecal case (Table 4.5).

Fig. 4.7 Rear view of a male nymph of Periplaneta australasiae, showing the proteinaceous secretion that accumulates on the cerci and terminal abdominal tergites. Photo courtesy of Thomas Eisner.

Cockroaches apparently have the enzymes required to break down the chitin polysaccharide chain; endogenous chitinase is distributed throughout the gut of P. americana (Waterhouse and McKellar, 1961). Exuvium consumption appears directly related to nitrogen budget in P. americana; the behavior occurs more commonly in females, in insects reared on a low-protein diet, and in those deprived of their fat body endosymbionts (Mira, 2000).

In addition to the direct consumption of bodies, body parts, and reproductive products, cockroaches feed on materials exuded from the body of conspecifics in several contexts (Table 4.6). A form of nuptial feeding occurs in most cockroach species whose mating behaviors have been studied. Tergal glands are common in mature male cockroaches (Chapter 6). The secretions they produce attract the female during courtship, and as she climbs onto the male's back to feed on them she is properly positioned for genital contact (Roth, 1969; Brossut and Roth, 1977). Tergal secretions are general phagostimulants, and gravid, unreceptive females as well as males and nymphs feed on the gland of a courting male (Roth and Willis, 1952a; LMR, unpubl. obs.; Nojima et al., 1999b). In at least two blattellid species, B. germanica and X. ha-mata, males use the secretion of the uricose (accessory) gland as a nuptial gift (Mullins and Keil, 1980; Schal and Bell, 1982). During auto- and allogrooming cockroaches may ingest cuticular waxes, as well as anything else on the body surface; they spend a significant amount of time grooming antennae, legs, feet, and wings (Bell, 1990). Fe-

Table 4.6. Conspecifics as food sources (modified from Nalepa, 1994).

Feeding behavior

Selected references

Cannibalism/necrophagy

Gordon (1959), Roth (1981a)

Oophagy (oothecae/

Nutting (1953b), Roth and

oothecal cases)

Willis (1954b),Willis et al. (1958),

Nalepa (1988a)

Consumption of exuvia

Roth and Willis (1954b),Willis et

al. (1958)

Male-female transfer

Tergal glands

Nojima et al. (1999b), Kugimiya

et al. (2003)

Accessory glands

Mullins and Keil (1980),Schal

and Bell (1982)

Cuticular secretions

Roth and Stahl (1956), Seelinger

(from grooming

and Seelinger (1983)

and cercal exudates)

Parental feeding

Stay and Coop (1973), Roth

(1981b), Perry and Nalepa

(2003)

Coprophagy

Cruden and Markovetz (1984),

Lembke and Cochran (1990)

males and nymphs of both sexes in a variety of oviparous species produce a grayish viscous secretion on the cerci and terminal abdominal segments (Fig. 4.7). The material reappears 5-10 min after molt or the removal of the secretion. During autogrooming of the glandular area, the upper layer of the secretion is removed by the hind tibia; the leg is then cleaned by drawing it through the mouthparts (Naylor, 1964). The material is primarily (90%) proteinaceous and may serve as supplemental food (Roth and Stahl, 1956). Nymphs have been observed ingesting it from each other (D. Abed and R. Brossut, pers. comm. to CAN). Newly molted cockroaches eat their exuvium together with the glandular material accumulated on it (Roth and Stahl, 1956). The secretion also serves in defense, by mechanically impairing small predatory arthropods (Roth and Alsop, 1978; Ichinose and Zenny-oji, 1980). Allogrooming has been observed in Pane. cri-brata (Rugg, 1987) and Cryptocercus punctulatus (Seelinger and Seelinger, 1983), neither of which produce this type of exudate. Neonates in at least six cockroach subfamilies feed on body fluids or glandular secretions of the mother (Chapter 8). These originate from a variety of locations on the adult body and have been analyzed only in the viviparous Diploptera punctata (Chapter 7).

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