Enwmologia Experimentalis etApplicata 77: 61-68, 1995. 61 (~) 1995 Kluwer Academic Publishers. Printed in Belgium.

Differential adaptation to water deprivation in first-instar nymphs of the German cockroach (Blattella germanica) and the brown-banded cockroach (Supella longipalpa)

Robert H. Melton Department of Ecology, Ethology, and Evolution, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Present address: U.S. Army Construction Engineering Research Laboratories, 2902 Newmark Drive, Champaign, IL 61801-9005, USA

Accepted February 2, 1995

Key words: water deprivation, food deprivation, metabolic water, Blattella germanica, Supella longipalpa, ecology, Dictyoptera, Blattellidae

Abstract

This study compares the relative abilities of first-instar nymphs of the german cockroach (Blattella germanica L.) and the brown-banded cockroach (Supella longipalpa E) to survive prolonged periods of food and/or water deprivation. S. longipalpa nymphs survived significantly longer than B. germanica nymphs when drinking water was absent, but the advantage of S. longipalpa over B. germanica disappeared if food was also absent. These results are consistent with the hypothesis that S. longipalpa is adapted to drier habitats than is B. germanica, and suggest that S. longipalpa nymphs may be more capable of producing and utilizing extra metabolic water from food than B. germanica nymphs. Evidence from the literature suggests that this species difference applies mainly to juveniles, since adults of B. germanica and S. longipalpa do not differ in ability to withstand water deprivation, regardless of food availability.

Introduction

The purpose of this investigation is to compare water- deprivation tolerance ability in first-instar nymphs of the brown-banded cockroach, Supella longipalpa E, and the german cockroach, Blattella germanica L.. The rationale for comparison of these two species' adaptation to water stress arises from comparisons of 1) geographical distributions of congeneric wild cock- roach species and 2) observed distributional differ- ences between the two species in human dwellings, both of which suggest that S. longipalpa may be bet- ter adapted to water-limited environmental conditions than B. germanica.

Both B. g ermanica and S. longipalpa are among the nuisance cockroach species of economic and hygien- ic importance (Cornwell, 1968). Capable of rapidly building to large populations, cockroaches are poten- tial vectors for a wide range of pathogens (Roth & Willis, 1957, 1960; Rueger & Olsen, 1969; Le Guyad-

er et al., 1989; Ash & Greenberg, 1980; Bell & Adiy- odi, 1981; Schal & Hamilton, 1991) and are high- ly allergenic (Frazier & Brown, 1980; Pollart et al., 1991) so that they can serve both as a source of infec- tive and immunological stress. The two species both infest human habitations such as houses, apartment buildings, office buildings, and food establishments (Cornwetl, 1968; Atkinson et al., 1990). Both species can occur together in the same building and even the same harborage (Gould & Deay, 1940, and pers. obs.). They are thus potential competitors for food, water, and shelter in human habitations.

The geographical origins of B. germanica and S. longipalpa are obscured by their present cosmopoli- tan distributions. Evidence regarding their habitats of origin, however, can be gleaned from considering the biogeography of their nearest congeneric relatives. The nearest relatives of B. germanica, according to Roth (1985) are Blattella asahinai (= beybienkoi), B. bisig- nata, and B. nipponica, of the germanica species

62

group. B. asahinai Mizukubo (the 'Asian cockroach', a recently introduced pest in Florida, U.S.A. (Bren- ner et al., 1988)) is listed by Roth as occurring in the Western part of south-east Asia, between India and Thailand while B. bisignata occurs more to the East between Thailand and the Phillipines. While these distribution data are not precise, congruence of these countries' boundaries with climatological and vege- tation maps such as those in the Times World Atlas (1993, 9th ed.) or Briggs & Smithson (1985) suggests that these species inhabit regions of primarily asea- sonal tropical equatorial rain forest, with abundant rainfall year-round, or with only a brief dry season compensated by abundant monsoons rains. B. nip- ponica is found in Japan, which, while not tropi- cal, nonetheless has a relatively moist climate. The two other species in the germanica species group are B. lituricollis, whose distribution includes many of the Micronesian islands, Indonesia, Malaysia, southeast Asia and the Thai peninsula, China, Japan, the Philip- pines, the Comoro Islands, Madagascar, and some parts of Africa (Kenya, South Africa, and Tanzania), and B. meridionalis, which is found in the Moluccas and some islands located between Celebes and Papua New Guinea. Again the distribution primarily includes regions of equatorial rain forest, although less clearly so in B. lituricollis. If these associations are correct, it seems likely that B. germanica initially evolved in a region of warm, humid, aseasonal tropical rainforest, in which water would not likely have been a limiting resource.

No correspondingly recent revision of the genus Supella is available, but Princis (1969) suggests an African origin. His classification lists under the sub- genus Supella, along with S. longipalpa, the species S. vicina from the Comoro Islands, S. dimidiata from Eritrea, Kenya, the Congo (Kinshasa), Ango- la, Zambia, Rhodesia (now Zimbabwe), Mozambique, Botswana, Southwest Africa (now Namibia), and parts of South Africa, and S. abbotti from Kenya, Tanza- nia, and Malawi. These are areas typified by tropical deciduous forest and savannah, with abundant annual rainfall but with a pronounced dry season. These distri- butions of congeneric species suggest that S. longipal- pa probably evolved under a regime of seasonally dry tropical rain forest or savannah, in which water would have been a seasonally limiting resource. This hypoth- esis is further suggested by Rehn's (1945) description of S. longipalpa as '...distributed over much of Africa outside of the Guinea forest areas'. Therefore, S. longi-

palpa might be expected to be better adapted to water- limited conditions than B. germanica.

Indirect evidence that B. germanica may be more strongly limited by water availability is also suggest- ed by the observed microhabitat preferences of the two species in homes. B. germanica tends to be found primarily in kitchens and bathrooms, whereas S. longi- palpa ranges more freely, being found commonly in closets, furniture, and drawers in various parts of the house, visiting the kitchen primarily to feed (Back, 1937; Gould & Deay, 1940).

Regarding the comparative adaptability of B. ger- manica and S. longipalpa to water shortage, both species must drink water to survive (Willis & Lewis, 1957), and the adult cuticles of these species do not sig- nificantly differ in their permeability to water (Appel et al., 1983). The study of Willis & Lewis (1957) (see Discussion) did not show any better survival rates in water-deprived S. longipalpa than in water-deprived B. germanica (juveniles were not tested). The oothecal lining of S. longipalpa is thicker and more resistant to desiccation than that of B. germanica (Roth, 1968). However, the B. germanica female provides water to her eggs through a water-permeable membrane form- ing the attachment between her body and the ootheca (Roth, 1955), whereas the S. longipalpa female choos- es a protected spot to lay her ootheca, deposits it, and then abandons it (McKittrick, 1964). Which maternal behavior pattern is better suited to protecting eggs from desiccation is not apparent a priori.

Materials and methods

Stock animals and rearing methods. Breeding stocks of B. germanica and S. longipalpa were obtained by trapping populations on the campus of the University of Illinois at Urbana-Champaign USA. The B. ger- manica came from a starting colony of 16 ootheca- bearing females collected from Morrill Hall during the spring of 1985, whereas the S. longipalpa were derived from 40 individuals (male and female, juveniles and adults) trapped in the Shelford Vivarium (approximate- ly 300 m from Morrill Hall) during the fall of 1986. The cockroach breeding stocks were maintained in five gal- lon plastic pails containing cohorts of animals hatched within a given week. Maintenance of a total of sev- en of such cohorts of B. germanica and ten cohort of S. longipalpa allowed access to a constant supply of cockroaches of all age and stage classes. Food and water were refreshed weekly and were available to

63

the stock animals at all times ad libitum. Details of daily stock rearing and maintenance procedures are described in Melton (1992).

The stock cohorts were fed Teklad@ standard lab- oratory rat chow. Purina@ Dog Chow was used in the experiments, partly because commercial dry dog food is a good cockroach diet (Alsop, 1990), and partly because it came packaged in appropriately-sized chunks to fit in the feeding vials.

it, rather than in the food vial, a strategem that was largely successful.

Live cockroach nymphs were weighed on a Met- tier AE 100 top-loading electronic scale to the nearest .0001 gram, without anesthetization, by chasing the nymph into a space between two small plastic cups (set one within the other), and then placing the entire assembly on the scale and reading the tared nymph mass.

Experimental conditions and weighing methods. All experiments were performed in a basement room. The photoperiod was maintained at L12:D12 in all exper- iments, a pattern suitable for two species of trop- ical origin. Ambient temperature varied because of the heating effect of the lights on the shelves, ris- ing to 29.0 ~ during the day cycle, and dropping to 26.7 ~ during the night cycle. Temperature at any given position on the shelf was consistent from day to day. Mean (4-standard deviation) ambient after- noon relative humidity levels, read between 1:00 pm and 5:00 pm, were 31.2% 4-5.2% r.h. during experi- ment 1 (N= 22 days), and 50.3%-4-4.6% r.h. during experiment 2 (N = 26 days). Relative humidity in the experimental housing cups was not measured, but was equalized as much as possible among the treatments by using organdy cloth screens (described below) as barriers to water access.

The experimental cockroaches were kept individ- ually in housing cups designed to permit controlled access to food and water. These were 9-ounce, dispos- able plastic drinking cups, with snap-on lids punctured with 5 small pinholes for air exchange. Petroleum jelly smeared around the inner rim retarded escape attempts. The cup was provisioned with a food vial, a water vial or dish, and a plastic bottlecap for shelter. The food vial was a 52 mm (height) x 15 mm (diameter) plastic scin- tillation vial with a screw-on cap. The cap was removed and replaced on the vial as needed to limit access to food. The water vials were 75 mm (length) x 12 mm (diameter) disposable glass culture tubes filled with distilled water, plugged with a ball of absorbent cot- ton, and placed mouth-downward in the cup at an angle that allowed access to the cotton by the cockroach. A small organdy screen was secured over the mouth of the tube with a rubber band. This screen was easi- ly removed and replaced as needed to limit access to water, and allowed evaporative water to humidify the inside of the cup at all times. A bottlecap was placed in the cup to encourage the cockroach to harbor under

Effect of water deprivation on survival. Two sepa- rate experiments were performed. Experiment 2 was a repeat of experiment 1, except that both food and water were manipulated to test for species x food • water interaction effects on nymphal survival.

Experiment 1 was conducted during March, 1988. The nymphs used were collected from samples of 100 oothecae per species, which hatched over a 3-day peri- od, and were therefore between 1 and 3 days old when the treatments began. From these nymphs, random samples of 56 nymphs per species were collected, weighed to the nearest 0.1 milligram, and random- ly allocated to one of two treatments, 'water' (8 ml of water provided per day) or 'no water' (water provision- ing discontinued after the first 24 h), and also randomly allocated a position on the shelf. Thus, a total of 112 nymphs were used, 28 nymphs per species-treatment combination. Nymphal survival was monitored daily. The experiment was terminated on the day of death of the last remaining water-deprived animal, the total duration of experiment 1 being 22 days. Control ani- mals still alive at the end of experiment 1 were assigned a survival time of 22 days.

Experiment 2 was conducted during July, 1989. The nymphs used were collected in a manner sim- ilar to experiment 1, except that the S. longipalpa eggs took longer to hatch than had been anticipated, and so first instar S. longipalpa were obtained directly from the stock cohort pails. Therefore, the B. german- ica nymphs were between 1 and 3 days old, and the S. longipalpa nymphs were between 1 and 7 days old. The 80 nymphs collected per species were weighed to the nearest 0.1 milligram, then randomly allocated to one of four treatments, and to a position on the shelf. Thus, a total of 160 nymphs were used, 20 nymphs per species-treatment combination, although a proce- dural error resulted in slightly unequal sample sizes (Table 1B). The 'food present, water present' (FW) group had both food and water available ad libitum. The 'food present, water absent' (FX) group had food available ad libitum but access to water was blocked

64

Table 1. Descriptive statistics for the initial wet masses of the Blatella germanica and Supella longipalpa nymphs used in (A) experiment 1, and (B) experiment 2. Treatment designations in (B) represent: 'FW' = 'Food Present, Water Present', 'FX' = 'Food Present, Water Absent', 'XW' = 'Food Absent, Water Present', and 'XX' = 'Food Absent, Water Absent'

A. Experiment 1

Species Treatment Mean Initial Standard

Wet Mass Deviation

(mg)

N

B. germanica Water 1.77 0.25 28

No Water 1.79 0.24 28

S. hmgipalpa Water 1.49 0.28 28

No Water 1.46 0.36 28

B. Experiment 2

Species Treatment Mean Initial Standard

Wet Mass Deviation

(mg)

B. germanica

S. longipalpa

FW 1.31 0.17 22

FX 1.42 0.21 20

XW 1.33 0.28 18

XX 1.35 0.16 20

FW 1.29 0.42 20

FX 1.46 0.44 20

XW 1.62 0.37 20

XX 1.51 0.50 20

after the first 24 h of the experiment. The 'food absent, water present' (XW) group had continual access to water but a cap was placed over the food vial after the first 24 h of the experiment, blocking access to food. Finally, in the 'food absent, water absent' (XX) group, access to both food and water was blocked after the first 24 h. Nymphal survival was monitored daily. The experiment was terminated on the day of death of the next-to-last resource-deprived animal remaining alive, the total duration of the experiment 2 being 26 days. Animals still alive at the end of experiment 2 were assigned a survival time of 26 days.

Each nymph, in both experiments, was categorized by level of the class variable 'Survival Time' = 'less than or equal to 10 days' vs. 'greater than 10 days'. This two-level class variable was used as the dependent vari- able in a categorical analysis of variance (logit analy- sis). The analysis of variance model for experiment 1 tested the significance of all main effects and interac-

tion effects among the two independent class variables, 'Species' (B. germanica vs. S. longipalpa) and 'Food' (Control vs. Deprived). The model for experiment 2 likewise tested the significance of all main effects and interaction effects among the three variables 'Species', 'Food', and 'Water' (Control vs. Deprived). Statistical significance of effects was accepted at the a =.05 level.

Calculations. All statistical analyses were performed using Statistical Analysis System (SAS) software (SAS Institute Inc., 1985) on an IBM 3081-GX2 mainframe computer. Life-tables, survivorship curves, and stan- dard errors of survivorship at day 10, for animals in both experiments, were calculated using the actuarial model option of the SAS LIFETEST procedure. Cate- gorical analyses of variance were calculated using the SAS CATMOD procedure, employing the maximum likelihood method.

Results

The mean initial wet masses at the beginning of exper- iment 1 were as shown in Table 1A. S. longipalpa started out at somewhat smaller average masses than did B. germanica, but average masses between treat- ments within species did not differ significantly (by t-tests). The effect of complete water-deprivation on first-instar nymphs is shown in Fig. 1. The controls for both species showed good overall survivorship. The experimental groups showed a strong species differ- ence, with a much longer survival time in S. longipalpa than in B. germanica. Categorical analysis of variance of the variable 'Survival Time' showed p-values for factor effects as follows: 'Species' p = .025, 'Water' p<.001, and 'Species x Water' p = .023. The results of experiment 1 are therefore best characterized for sur- vival at day 10 by a 'Species x Water' interaction sig- nificant at the 0.05 level. This interaction appears to be related to a longer average survival time in S. longipal- pa than in B. germanica under water deprivation.

Initial wet masses of the starting populations for experiment 2 are presented in Table lB. The effects of food-deprivation and/or water-deprivation on the sur- vivorship of first instar nymphs in experiment 2 are shown in Fig. 2. The outstanding feature is the high survivorship of S. longipalpa under water-deprivation when food is present compared to the low survivorship when food is absent. Categorical analysis of variance of the variable 'Survival Time' showed p-values for factor effects as follows: 'Species' p =.866, 'Food'

1.o

0.0

(5 Z 0.8

ft"

Ca') 0.6

Z O ~--- 0.4 n- O Q. O CC 0 .2 . n

2 4 8 1 0 1 2 1 4 1 6 1 8 2 0

BG - Water

BG - No Water

�9 SL - Water

$ L - No Water

TIME (DAYS)

Fig. 1. Life-table survival rates from experiment 1 for B. germanica (BG) and S. longipalpa (SL) first instar nymphs in the presence vs.

absence of available drinking water. Vertical bars represent standard errors of proportion of survival at 10 days from the start of the experiment.

p<.0001, 'Species • Food' p= .956, 'Water' p = .026, 'Species x Water' p =.110, 'Food • Water' p =.007, and 'Species , x Food x Water' interaction p = .039. The results of experiment 2 are therefore best char- acterized at day 10 by a 'Species x Food x Water' interaction significant at the 0.05 level. This interac- tion appears to be related to a longer average survival time in S. longipalpa than in B. germanica under water deprivation when food is present (treatment 'FX'), but not when food is absent (treatment 'XX').

65

z > >

l J3 Z o_ F-

=o O Q.

l o . . . . . . . . . . . . . .

0.8- ~ T B. germanica

0.6 ~ ~ ~ ~w

~ ........... :~ ...... XW 0.4- it ~ xx

0.2" ! ~

0.0 . , �9 , . i �9 , . . , . ~ �9 0 2 4 6 8 10 12 14 16 18 20 22 ;>4 26

1.0

z 0.8 _> >

--1 0.6 o3 z O P ,',-' 0.4 0 0.- 0

ct. 02 "

0.0

g

s. Iongip lpa 1

2 4 6 8 10 12 14 16 18 20 22 Z4 26

TIME (DAYS)

Fig. 2. Life-table survival rates f rom experiment 2 for B. germanica and S. longipalpa first instar nymphs in the presence vs. absence of available food and/or water. Vertical bars represent standard errors of proportion of survival at 10 days from the start of the experiment. The treatment designations are defined as in Table I(B).

Discussion

Experiment 1 showed a strong difference between B. germanica and S. longipalpa nymphs in their abil- ity to survive when drinking water was absent. The results of experiment 1 are replicated in experiment 2 (in the FW and FX treatments), with the exception of a slightly poorer survival in the S. longipalpa FW controls relative to the B. germanica controls. Experi- ment 2 additionally showed that the survival advantage ofS. longipalpa over B. germanica nymphs when water was absent disappeared if food was also made unavail- able. Differences among treatment groups in the initial

masses of these animals did not correspond with, or help to explain, any of these results.

There is no reason to believe, in either experiment, that there were differences among treatments in rela- tive humidity within the housing cups, water available in the food, or cuticular exposure to moisture, so that the observed results cannot be explained by differ- ences in water intake other than drinking, which was under experimental control. The most likely difference between the species, that would produce the results of both experiments, is a difference in their abilities to produce and utilize extra water from the metabolism of food. Such an ability would appear to be greater

66

in first instar nymphs of S. longipalpa than those of B. germanica. The ability to produce extra metabol- ic water from food for use under dry conditions has been reported in a number of insect species (Wharton, 1985; Edney, 1977; Jindra & Sehnal, 1990), espe- cially in those that develop on substances with a low water content, such as flour, grain, fishmeal, or wool (Fraenkel & Blewett, 1944). The presence of such a mechanism in S. longipalpa, but not in B. germanica, nymphs suggests that the former species is adapted to drier conditions than is the latter.

The results of a similar experiment by Willis & Lewis (1957), using adults of B. germanica and S. longipalpa (among other cockroach species), pro- vide an interesting comparison with the results of the present study. In that study (Fig. 3) access to water appeared to benefit B. germanica females more than S. longipalpa females in the absence of food. However, neither S. longipalpa females nor males survived better under water-deprivation than adults of B. germanica, and there was no evidence that access to food mitigated the effects of water-deprivation in adult S. longipalpa. The results of Willis & Lewis and the results presented here appear to be contradictory unless we accept the hypothesis that S. longipalpa begins life at hatch with an ability to produce and use extra metabolic water, but largely loses this ability in the adult stage. B. german- ica, on the other hand, appears to begin life equally vulnerable to water deprivation and food deprivation, but as adults the females (but not males) become more resistant to the effects of food deprivation than S. longi- palpa as long as drinking water is available.

A decrease in metabolic water production over development in S. longipalpa could be the result of changing selection pressures over development, a decreasing need for supplementary water as body size increases, relative to the energetic costs of extra metabolic water production. Regarding need for water, nymphs, being smaller than adults, have larger sur- face/volume ratios, making them more vulnerable to desiccation (Schmidt-Nielsen, 1984). Nymphs are also weaker than adults, less vagile, and less capable of moving between food and water sources. Regarding metabolic costs, intracellular energy flow is controlled by the ATP/ADP ratio, such that extra water produc- tion through increased metabolism cannot be achieved unless concomitant ATP accumulation is prevented, either by (1) reducing ATP generation (uncoupling mitochondrial respiration from ATP production) or by (2) increasing ATP utilization (e.g. increasing muscu- lar activity or biomass production). The first method

>.

g0 - MALES FEMALES

�9 i so -: ]~

B. german/ca

70 - S. /onglpalpa

60 "

5 0 -

3 0 '

20

0 . . . . . . . . . .

>-

uJ r~ z 0 ,_1

XX XW FX FW XX XW FX FW

T R E A T M E N T

Fig. 3. Comparison, from Willis & Lewis (1957), of mean survival durations of adult B. germanica and S. longipalpa in the presence vs. absence of food and/or water, when isolated individually in containers at 27 ~ and 40% relative humidity. Vertical bars repre- sent 1 standard error. The treatment designations are defined as in Table I(B). Survival times in the FW controls do not entirely reflect mortality, many control animals being alive at the end of the exper- iment. Survival times in all other treatments reflect actual deaths. Sample size is N= 10 for all means, except N=9 for S. longipalpa 'XW' females.

requires that energy be produced at a rapid rate without being chemically stored, whereas the second method could lead to unwanted excess activity or biomass production. Fraenkel & Blewett (1944) reported that increased facultative use of metabolic water entails decreased efficiency of conversion of ingested food into biomass, and decreased development rates, in Tribolium, Ephestia, and Dermestes. Thus, in these species, any extra energy produced along with extra metabolic water did not contribute to growth. Higher average muscular activity levels in S. longipalpa than in B. germanica nymphs could result in higher rates of metabolic water production in the former species. This explanation seems unlikely but cannot be ruled out, since activity levels were not monitored during the present study, and have not been compared between these species in other studies to date.

The present evidence supports the hypothesis that S. longipalpa is better adapted to water-limited envi- ronmental conditions than B. germanica, but also implies that such adaptation in S. longipalpa is strong- ly dependent on the availability of food, and on the developmental stage being considered. S. longipalpa could have a selective advantage over B. germanica in dry, desiccating environments, especially if food is available but standing water sources in short supply.

Therefore, S. longipalpa is predicted to fare better in competition with B. germanica in human habitations comprising arid environments, such as buildings in deserts, or in temperate regions (if well-heated) during winter. Ecological studies comparing the distribution and population dynamics of these two species when they occur together in buildings, in relation to avail- able food and water sources are warranted.

Also warranted are physiological studies of onto- genetic changes in the interaction of food intake and water balance in B. germanica, S. longipalpa, and other cockroach species. One possible study would compare different developmental stages of B. germanica and S. longipalpa using the methods of Jindra & Sehnal (1990) to determine the extent to which mitochondri- al respiration is uncoupled from ADP-to-ATP conver- sion. Endogenous coupling of respiration to ATP pro- duction is predicted to be lower in early-instar nymphs ofS. longipalpa than on B. germanica, and an increase in the degree of such endogenous coupling over the progress of development is predicted for S. longipal- pa, whereas none is predicted for B. germanica.

Acknowledgments

I wish to thank Drs. A. W. Ghent, G. O. Batzli, G. Wald- bauer, M. Berenbaum, and S. E. Franson for their crit- ical suggestions and encouragement during the course of this work. I also thank former undergraduate stu- dents Tim Alikakos, Joi Brooks, Anish Chatterjee, Kenney Choi, David Kirby, Soo Wang Lee, Eve Levin, Jim Masterson, Richard Park, Saki Ratanawong, and Melissa Tomczak for their assistance in the laboratory with rearing and experimental procedures at various times, and thank the University of Illinois at Urbana- Champaign for providing space, equipment, and sup- plies used in this work.

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