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Invertebrate herbivory in a Texas playa lake.

Herbivory as an ecological process is considered minor compared to the detrital energy pathway in defining the function of freshwater wetlands (Mitsch and Gosselink, 1986). Smith (1988) found no evidence for vertebrate herbivory in playa lakes dominated by Typha sp. Recent studies have shown that invertebrates can remove a substantial amount of herbage in wetlands (Scott and Haskins, 1987; Foote et al., 1988). The objectives of this paper are to report 1) the presence of invertebrate herbivory in a playa lake, 2) a new geographic record for a species of Chrysomelidae, 3) differences between sexes in the quantity of herbivory by a species of Chrysomelidae in playa lakes, and 4) to discuss the potential of this species as a biological control for a plant species in playa lakes.

I observed invertebrate herbivory in a playa lake 4 km. NW Floydada, Floyd Co., Texas, during the summers of 1989 and 1990. The herbivore was Gastrophysa dissimilis (Say) (Coleoptera: Chrysomelidae). Herbivory was accomplished by larvae during 1989 and primarily by adults during 1990. This species has not been reported in Texas. Previous reports of G. dissimilis are for Utah, Missouri, and Kansas (Wilcox, 1972; Riley and Enns, 1979).

White et al. (1984) generalized that most chrysomelids have a distinct preference for a single plant species as a host. Wilcox (1972) reported G. dissimilis as being found on Polygonum sp. Riley and Enns (1979) listed specimens found on Rumex verticullatus and Polygonum sp. I found G. dissimilis exclusively on Persicaria (=Polygonum by some authors) coccinea. I followed Correll and Johnston (1979) in using Persicaria rather than Polygonum as the generic name for the species.

In August 1991, the area of the lake was determined, from transit angle and distance data, to be 15.3 hectares. Frequency of all plant species was evaluated along five evenly spaced, parallel transects across the lake. Individual species frequency was measured in quadrats 10 centimeters in diameter that were located at five-meter intervals along each transect (202 total quadrats). Any plants within quadrats that had evidence of herbivory (for example, chewed parts, insect presence) were noted.

Frequency data were used to estimate the area of all Persicaria sp. in the lake. Persicaria coccinea covered 85.4 percent (13.1 hectares) of the lake, whereas P. pensylvanica and P. lapathifolia covered 12.2 percent (1.9 hectares) and 1.0 percent (0.2 hectare) of the lake, respectively. However, only leaves of P. coccinea had any evidence of herbivory in that 65.7 percent (8.6 hectares) of all individuals indicated the presence of G. dissimilis.

The actual amount of herbage removed by G. dissimilis in the field was not estimated because individual leaves died when parts were eaten and the uneaten portion (mostly midribs) rapidly disintegrated. The lack of new leaf growth on individuals of P. coccinea that had been partially eaten indicated no compensatory growth in response to herbivory.

The potential amount of herbivory by male and female G. dissimilis on leaves of P. coccinea was measured in the laboratory. The area of 18 P. coccinea leaves were measured with a LI-COR, Inc. LI-3100 area meter. Each leaf was placed on a moistened paper towel in separate petri dishes. Three replicates each of male and female G. dissimilis at one, two, and three individuals per leaf were placed in the petri dishes. Females were identified by the presence of an egg sac. Seven days later, the remaining area of each leaf was measured.

Females consumed more of the leaf as compared to males (Fig. 1). This was expected because females were producing eggs. Also, as expected, increasing the number of individuals per leaf for males and females increased the total consumption of the leaf (Fig. 1). A considerable percentage of the leaf area was consumed by both male and female G. dissimilis, especially at three individuals per leaf (approximately 60 and 20 percent for females and males, respectively--see Fig. 1). Therefore, the amount of P. coccinea consumed by G. dissimilis adults is potentially large. Loss of this amount of photosynthetic tissue may be sufficient to alter the function of playa lakes. This possibility should be a subject of further research.

Playa lakes are important wintering areas for waterfowl (Anonymous, 1988). Waterfowl in playas need seeds from native vegetation for a balanced, nutritious diet (Baldassarre et al., 1983). However, P. coccinea produces little seed compared to other species of Persicaria (Haukos, unpublished data). Also, because P. coccinea is a rhizomatous perennial (Correll and Johnston, 1979), it is capable of dominating a playa lake (personal observation) and preventing the germination and seed production of desirable annual species for waterfowl (Haukos, 1991). It is apparent that G. dissimilis is unable to eliminate P. coccinea when the latter is widespread in a playa. However, it is possible that when P. coccinea starts to invade a lake, translocation of sufficient quantities of G. dissimilis may provide a biological control, which would eliminate or retard the invasion of P. coccinea. This would allow more desirable species to continue to produce seed in the playa for waterfowl.

[FIGURE 1 OMITTED]

I would like to thank E. G. Riley of Texas A & M University for confirming the identification of G. dissimilis and providing pertinent citations for Chrysomelidae. Vouchers of G. dissimilis are in the Texas Tech University Entomological Collection and W. R. Enns Entomology Museum, University of Missouri. L. M. Smith and H. L. Schramm, Jr., reviewed the manuscript. This is paper T-9-625 of the Texas Tech University, College of Agricultural Sciences.

LITERATURE CITED

Anonymous. 1988. Playa lakes region waterfowl habitat concept plan, category 24 of the North American Waterfowl Management Plan. U.S. Fish and Wildlife, Albuquerque, New Mexico, 37 pp.

Baldassarre, G. A., R. J. Whyte, E. E. Quinlin, and E. G. Bolen. 1983. Dynamics and quality of waste corn available to postbreeding waterfowl in Texas. Wildlife Soc. Bull., 11:25-31.

Correll, D. S., and M. C. Johnston. 1979. Manual of the vascular plants of Texas. Univ. Texas at Dallas Press, Richardson, Texas, xiii+1881 pp.

Foote, A. L., J. A. Kadlec, and B. K. Campbell. 1988. Insect herbivory on an inland brackish wetland. Wetlands, 8:67-74.

Haukos, D. A. 1991. Vegetation manipulation strategies for playa lakes. Unpublished Ph. D. dissertation, Texas Tech Univ., Lubbock, xiii+175 pp.

Mitsch, W. J., and J. G. Gosselink. 1986. Wetlands. Van Nostrand Reinhold, New York, xiii+537 pp.

Riley, E. G., and W. R. Enns. 1979. An annotated checklist of Missouri leaf beetles (Coleoptera: Chrysomelidae). Trans. Missouri Acad. Sci., 13:53-83.

Scott, M. L., and J. L. Haskins. 1987. Effects of grazing by chrysomelid beetles on two wetland herbaceous species. Bull. Torrey Bot Club, 114:13-17.

Smith, L. M. 1988. Lack of vertebrate herbivory in playa wetlands. Wetlands, 8:193-197.

White, D. S., J. T. Doyen, and W. U. Brigham. 1984. Aquatic Coleoptera. Pp. 361-437, in An introduction to the aquatic insects of North America (R. W. Merritt and K. W. Cummins, eds.), Kendall/Hunt Publ. Co., Dubuque, Iowa, xiii+722 pp.

Wilcox, J. A. 1972. A review of the North American Chrysomeline leaf beetles (Coleoptera: Chrysomelidae). Bull. New York State Sci. Ser., 421:1-37.

DAVID A. HAUKOS

Department of Range and Wildlife Management, Texas Tech University, Lubbock, Texas 79409
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Title Annotation:GENERAL NOTES
Author:Haukos, David A.
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:May 1, 1992
Words:1204
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