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There is little evidence that any cockroach species is able to subsist solely on the mature green leaves of vascular plants. There are reports of occasional herbivory, such as that of Crowell (1946), who noted that the small, round leaves of the aquatic plant Jussiaca are included in the diet of Epilampra maya. Often, cockroaches that appear to be feeding on green leaves are actually eating either a small, dead portion at the leaf edge or around a hole, or other material on the leaf (WJB, unpubl. obs.). To test the extent to which tropical cockroaches include fresh vegetation in their diets, WJB set up a series of two-choice tests in laboratory cages at La Selva Biological Station in Costa Rica. Ten species of cockroaches were tested: Capucina sp., Cariblatta imitans, Epilampra involucris, Ep. rothi, Ep. unistilata, Latiblattella sp., Imblattella impar, Nahublat-tellasp., Nesomylacrissp., and X hamata. The insects were offered a choice of green leaves versus dead leaves of the same plant species; only leaves eaten readily by local Or-

Table 4.3. Longevity of cockroaches on starvation diets.Tests were performed at 36-40% relative humidity,except for tests with R.maderae, which were run at 70%. Note that controls (+ food, + water) are not adult lifespans; controls were terminated when all the experimental insects of the species died. Modified from Willis and Lewis (1957).

Species

Blattidae Blatta orientalis

Neostylopyga rhombifolia

Periplaneta americana

Eurycotis floridana

Blattellidae Blattella germanica

Blattella vaga

Supella longipalpa

Blaberidae Diploptera punctata

Rhyparobia maderae

Nauphoeta cinerea

Pycnoscelus surinamensis thoptera were used. The feeding behavior of the cockroaches was observed throughout the night, and their guts dissected the next day. Without exception, no cockroach ate fresh vegetation. Individuals that nibbled the greenery appeared repelled and on occasion could be observed jumping away from the leaf. When offered a choice of paper versus green leaves, the cockroaches ate the paper. When only green leaf was offered, they refused to feed.

Nonetheless, there are numerous records of cockroaches as plant pests (Roth and Willis, 1960). In 1789, Captain William Bligh had to wash down his ships with boiling water so that cockroaches would not destroy the breadfruit trees he was transporting from Tahiti to the West Indies (Roth, 1979a). One of the more frequently reported plant pests is Pycnoscelus surinamensis, which destroyed the roots of 300,000 tobacco plants in Sumatra. In

Mean length of survival (days)

Female

64

16.8

32.1

14.2

Male

40

11.5

20.0

11.9

Female

108

25.4

26.7

22.1

Male

128

24.6

29.3

21.9

Female

190

40.1

89.6

41.7

Male

97

27.3

43.7

28.1

Female

86

26.6

43.0

26.7

Male

70

21.8

29.7

21.1

Female

85

11.9

41.9

12.8

Male

54

8.8

9.6

8.2

Female

95

7.9

32.4

8.5

Male

69

5.4

16.8

4.8

Female

80

12.8

14.3

14.5

Male

74

11.5

10.1

9.0

Female

102

18.7

42.9

18.7

Male

119

14.5

28.9

15.8

Female

181

160.0

54.3

51.3

Male

150

84.0

56.0

35.1

Female

98

24.3

61.1

27.0

Male

94

22.8

46.1

27.3

Female

139

18.8

73.2

24.3

Male

74

9.9

39.8

10.6

greenhouses, it is known to girdle rose bushes, eat the bark and stems of poinsettias, and damage orchids, cucumbers, and lilies. It was responsible for the destruction of 30,000-35,000 rose plants in one Philadelphia greenhouse, and regularly hollows the hearts of palms and ferns in the southern United States (Roth, 1979a). Apparently, it managed to sneak into Biosphere 2 and took a strong liking to every kind of living plant. Tomatoes, sweet potato leaves, flowers and fruit of squash plants, rice seedlings, ripe papayas and figs, and green sorghum seeds were each included on the bill of fare (Alling et al., 1993). While the culprit cockroach was never identified, both Pyc. surinamensis and P. australasiae were found in the beehives brought in to pollinate crops (Susan C. Jones, pers. comm. to CAN).

The most commonly reported type of plant damage by cockroaches is to seedlings, new leaves, and growing root and shoot tips. These are likely preferred because their actively growing tissues have physically tender, thin-walled cells, lower levels of secondary compounds, and higher levels of nitrogen than mature leaves (Chown and Nicol-son, 2004). Examples include P. americana destroying 30% of the freshly planted seeds of the quinine-producing plant Cinchona pubescens in Puerto Rico (Roth, 1979a), and Shelfordina ( = Imblattella) orchidae damaging developing roots and shoots of orchids in Australian greenhouses (Rentz, 1987). Calolampra elegans and Cal. solida (Blaberidae) are pests requiring control measures in a variety of Australian crops, including sunflower, soybean, sorghum, cotton, navy beans, wheat, and maize. The cockroaches live in litter and the upper layers of soil, and emerge at night to chew the stems of seedlings at or near ground level (Robertson and Simpson, 1989; Murray and Wicks, 1990; Roach and Rentz, 1998). Cockroach herbivory in tropical forests is probably more common than generally realized; damage to newly flushed leaves in the canopy of Puerto Rican rainforest has been correlated with the abundance of cockroaches (Dial and Roughgar-den, 1995).

Overt herbivores are not limited to feeding on green leaves of vascular plants; the category includes organisms that feed on other plant parts as well (Hunt, 2003). Many cockroach species, then, are at least partly herbivorous, because they include pollen, nectar, sap, gum, roots, bark, twigs, flowers, and fruit in their diet. Among those known to feed on pollen are Sh. orchidae (Lepschi, 1989), Para-tropes bilunata (Perry, 1978), Latiblattella lucifrons (Helfer, 1953), and Ellipsidion sp. (Rentz, 1996). Balta bicolor is commonly found on the leaves and spent flower heads of Gahnia sp. in eucalypt woodlands (Rentz, 1996) and both males and females are attracted to pollen placed on a tree branch (Fig. 4.3). In a survey of insects captured by the pitcher plant Sarracenia flava in North Carolina, CAN (unpubl. data) collected males of four species of Parcoblatta (Parc. fulvescens, Parc. uhleriana, Parc. virginica, and Parc. lata), and both sexes of Cariblatta lutea. Since all these are winged as adults, while females of the Parcoblatta species are brachypterous, the cockroaches may be seeking nectar as an easily harvested source of energy to fuel flight. This suggestion is strengthened by the observation that volant Blattella asahinai adults, but not nymphs, feed on aphid honeydew (Brenner et al., 1988). Trichoblatta sericea in India feeds on the gum exuded from the bark of Acacia trees, and less commonly on gum from other trees (Azadirachta, Moringa, Enterolobium) (Reuben, 1988). Since individuals lived twice as long and had four times the reproductive output when fed a diet of powdered gum arabic when compared to a diet of biscuit crumbs or wheat flour, gum may be providing essential nutrients. The digestive physiology of this species would be of interest, as most gums are carbohydrate polymers that require microbial degradation if they are to be assimilated (Adrian, 1976). A number of cockroaches are noted as feeding "on flowers" (e.g., Opisthoplatia orien-talis—Zhu and Tanaka, 2004a; Ectobius pallidus—Payne, 1973), but it is unclear as to whether the individuals were actually feeding on flower petals, or standing on the flower ingesting pollen or nectar. Arenivaga apacha (Cohen and Cohen, 1976) and possibly other cockroaches that dwell in vertebrate burrows feed on the stored seeds of their host, while sand-swimming species of Arenivaga include the roots of desert shrubs in their diet (Hawke and Farley, 1973). Many species feed on ripe fruit, an energy-rich, seasonally available food source. Diplotera punctata, for example, feeds on mangoes, papayas, and oranges, as well as on the outer covering of Acacia pods (Bridwell and Swezey, 1915) and the bark of Cypress, Japanese cedar, citrus, and Prosopis spp. (Roth, 1979a).

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