Sexual Differences

Current evidence suggests that male foraging behavior and food choice differs from that of females; generally, male cockroaches feed less and on fewer food types. In the Costa Rican rainforest male cockroaches always have less food in their guts than do females after the usual nightly foraging period (WJB, unpubl. data). This is particularly true for seven species of blattellids, in which 50-100% of males had empty guts. In more than 30 male Latiblattella sp. examined, none had any food in the gut. In contrast, males of four species of blaberids often had medium to full guts, although females had still fuller guts. This difference may be due to the active mate searching required of blattellid males as compared to blaberids. Male cockroaches tend to have narrower diets than females (Table 4.2), which may relate to the nutrients required for oogenesis. A similar pattern was obvious in D. punctata in Hawaii; 44% of females had guts filled to capacity, whereas male guts were never full. Nymphal guts were variable (19% full, 81% not full). It appeared that first instars had not fed at all, suggesting that they were relying on fat body reserves developed in utero while being fed by their viviparous mother. Older nymphs had fed to repletion. In all stages, the gut content was homogeneous material resembling dead leaf mush (WJB, unpubl. data). The amount of food consumed by male P. americana varies greatly on a daily basis, with the insects fasting on approximately one-third of days (Rollo, 1984b). Male German cockroaches did not exhibit cyclical feeding patterns, but the degree of sexual activity appears influential.

Table 4.1. Diet of four species of Parcoblatta, based on 45 nocturnal observations of feeding adults (Gorton, 1980). Note that two species were not observed ingesting animal food sources.

Pare. pennsylvanica Pare. uhleriana Pare. lata Pare. virginica

Cambium +

Flower petals +

Cercropid spittle +

Live insect +

Bird feces +

Mammalian feces +

Mammalian cartilage +

0 1234 56789 10 EC ECD EC ECD

Days of the Reproductive Cycle

Fig. 4.1 Dietary self-selection in cockroaches. (A) Mean intake of protein and carbohydrate (CHO) cubes and cumulative percent molting in Supella longipalpa first instars over the course of the stadium. From Cohen et al. (1987), courtesy of Randy W. Cohen. (B) Food consumption by adult female Parcoblattaful-vescens over the course of the reproductive cycle when given a dietary choice. Dashed line, 5% protein-cellulose diet; dotted line, 5% protein-dextrose diet; solid line, 42% protein diet. EC, egg case formation; ECD, egg case deposition. From Lembke and Cochran (1990), courtesy of Donald G. Cochran. Both graphs reprinted with permission of Elsevier Press.

0 1234 56789 10 EC ECD EC ECD

Days of the Reproductive Cycle

Fig. 4.1 Dietary self-selection in cockroaches. (A) Mean intake of protein and carbohydrate (CHO) cubes and cumulative percent molting in Supella longipalpa first instars over the course of the stadium. From Cohen et al. (1987), courtesy of Randy W. Cohen. (B) Food consumption by adult female Parcoblattaful-vescens over the course of the reproductive cycle when given a dietary choice. Dashed line, 5% protein-cellulose diet; dotted line, 5% protein-dextrose diet; solid line, 42% protein diet. EC, egg case formation; ECD, egg case deposition. From Lembke and Cochran (1990), courtesy of Donald G. Cochran. Both graphs reprinted with permission of Elsevier Press.

The food intake of B. germanica males mated twice per week was greater than that of males allowed to mate only once (Hamilton and Schal, 1988).

In many oviparous females, food intake and meal type is correlated with the ovarian cycle. Food intake falls to a low level a few days prior to ovulation and remains low until the ootheca is deposited in P. americana (Bell, 1969), Parcoblatta fulvescens, Parc. pennsylvanica (Cochran, 1986b), Su. longipalpa (Hamilton et al., 1990), and B. germanica (Cochran, 1983b; Cloarec and Rivault, 1991; Lee and Wu, 1994). Water intake is also cyclical (Fig. 4.2) (Cochran, 1983b, 1986b). In the ovoviviparous R. maderae, food intake declines at the time of ovulation and remains at a relatively low level until partition; neural input from mechanoreceptors in the wall of the brood sac directly inhibits feeding (Engelmann and Rau, 1965). In pregnant females of D. punctata, gut fullness varies relative to embryo length, with a trend toward full guts when embryos are small (2-5 mm) and empty guts when embryos are large (6-8 mm) (WJB, unpubl. data).

Females in at least two blattellid species select among various food types according to their vitellogenic requirements. In choice experiments with Xestoblatta hamata, Schal (1983) found that high-nitrogen foods were consumed mainly on nights 3 and 4 of the ovarian cycle. Females of Parc. fulvescens given one high-protein and two low-protein diets fed so that they remained in nitrogen balance; relative proportions of the different nutrients varied over the reproductive cycle (Fig. 4.1B). Females with access to only high-protein diets excreted urates, an indication that ingested protein levels exceeded their needs. Ovarian cycles of the self-selecting individuals were similar in length to those of the females fed a high-protein diet (Cochran, 1986b; Lembke and Cochran, 1990).

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