PROC. ENTOMOL. SOC. WASH. 93(3), 1991. pp. 748-750 GROWTH EFFICIENCY IN JUVENILE MANTIDS: ABSENCE OF SELECTION FOR OPTIMIZATION IN A FOOD-LIMITED ENVIRONMENT (ORTHOPTERA: MANTIDAE) HuRD L. E. Ecology Program, School ofLife Sciences, University ofDelaware, Newark, Delaware 19716. Abstract.—First instar mantids, Tenodera aridifolia sinensis (Saussure), were offered prey at six different densities in a replicated laboratory experiment. Although predation rate consistently increased with increasing prey density, growth efficiency reached a peak (58%) at intermediate prey density, and declined to 40% at the highest prey density. This decline, which represents a decrease in assimilation efficiency at the most rapid feeding rates, depicts wastage offood and reflects the lack ofselection for optimization in food limited environments. Key Words: predation rate, prey density, growth efficiency, feeding rates. The Chinese mantid, Tenodera aridifolia tids in that experiment to clarify how sinensis(Saussure), isageneralistarthropod nymphs fed at rates beyond their ability to predator which inhabits a wide variety of benefit from increasing prey densities. early successional habitats in Delaware and Materials and >4ethods much ofthe eastern United States (Gumey 1950, Hurd and Eisenberg 1989). Egg hatch An experimental cohort of T. a. sinensis typically occurs early in the spring when nymphs was derived from oothecae col- prey availability for first instar nymphs is lected in New Castle County, Delaware low (Hurd 1988). Most mortality occurs (Hurd and Rathet 1986). Nymphs were during the first stadium, chiefly as a result maintained individually in 130 ml glass vi- of food limitation (Hurd and Eisenberg als, beginning immediately upon hatching. 1984). These were divided into six treatment Hurd and Rathet (1986) addressed the groups, representing different prey densi- question of whether, in view of heavy se- ties, consisting of20 nymphs each. Densi- lection against the first stadium, mantid ties ofprey (Drosophila melanogaster Mei- nymphs could optimize predation rate gen) were established by varying the rate of (functional response) to achieve maximum supply among groups: group I = 0.33 flies/ = development rate and size at first ecdysis day (one fly every three days), group II undera variety ofprey densities in the lab- 0.50 flies/day,groupIII = 1.0 fly/day,group oratory. We found that nymphs which suc- IV = 2.0 flies/day, group V = 3.0 flies/day, cessfully completed the first stadium in- andgroup VI = ad libitum (flieswereadded creased predation rate beyond that which in excess ofdepletion). These mantids were produced gains in both ofthese life history kept in incubators at 23°C on a 12:12 L:D parameters,anapparentlywastefulstrategy. light cycle. Here I examinegrowthefficienciesforman- Numbers of flies consumed, whole or in VOLUME 93, NUMBER 3 749 Table 1. Mean(±SE)predation rate(flies/mantid/ 60 day), dry weight biomass at ecdysis, and dry weight biomass ofprey eaten during first stadium for T. si- nensis nymphs in six experimental groups. Group 750 PROCEEDINGS OFTHE ENTOMOLOGICALSOCIETY OFWASHINGTON nets ofoptimal foraging theory, such as re- density manipulations ofthe predator Tenodera jectingsuboptimalprey(StephensandKrebs sinensisSaussure(Orthoptera:Mantidae)inanold- 1986). Most studies of the relationship of field community. I. Mortality, development and dispersal ofjuvenile mantids. Journal ofAnimal various arthropod predators to their prey Ecology 53: 269-281. sources have revealed some degree offood 1989. Temporaldistributionofhatchingtimes limitation (e.g. Mukerji and LeRoux 1969, inthreesympatricmantids(Mantodea: Mantidae) Lawton 1971, Wise 1975, 1979, Takafuji with implications for niche separation and coex- and Chant 1976, Formanowicz 1982, Len- istence. Proceedingsofthe EntomologicalSociety ofWashington 91: 55-58. ski 1984, Folsom and Collins 1984). There- Hurd, L. E. and I. H. Rathet. 1986. Functional re- fore in the real world such predators gen- sponse and success injuvenile mantids. Ecology erally may provide poor fit to optimization 67: 163-167. models. Lawton, J. H. 1971. Maximum and actual feeding- rates in larvae of the damselfly Pyrrhosoma Acknowledgments nymphula (Sulzer) (Odonata: Zygoptera). Fresh- water Biology 1: 99-111. This work was supported in part by NSF Lenski,R.E. 1984. Foodlimitationandcompetition: grant BSR 8506181. 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