PERSPECTIVES 335 Res. Board Influences of Diet on the Life Histories of Aquatic Insectsi,2 toplankton toxicants, N. H. ANDERSON AND KENNETH W. CUMMINS Fish. Res. Department of Entomology and Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331, USA iver into a !33. ,RAM. 1975. ANDERSON, N. H., AND K. W. CUMMINS. 1979. Influences of diet on the life histories of aquatic le effect of insects. J. Fish. Res. Board Can. 36: 335-342. growth of Benthic species are partitioned into functional feeding groups based on food-acquiring mechanisms. Effects of food quality on voltinism, growth rate, and size at maturity are demon- I larvae of strated for representatives of gougers and shredders, collectors, and scrapers. Food quality for iscidae). J. predators is uniformly high, but food quantity (prey density) obviously influences their life histories. A food switch from herbivory to predation, or some ingestion of animal tissues, in large dams stream flow the later stages is a feature of the life cycle of many aquatic insects. Temperature interacts with and C. H. both food quality and quantity in effects on growth as well as having a direct effect on control of metabolism. Thus further elaboration of the role of food in life history phenomena will d seasonal require controlled field or laboratory studies to partition the effects of temperature and food. .ructure of Key words: aquatic insects, feeding strategies, functional groups, life histories i. W. Esch II, ERDA ANDERSON, N. H., AND K. W. CUMMINS. 1979. Influences of diet on the life histories of aquatic G. ATCHI- insects. J. Fish. Res. Board Can. 36: 335-342. esponse of Nous avons separd les especes benthiques en groupes, selon le type dalimentation fonc- containing tionnelle ton sur les mecanismes dacquisition de la nourriture. Chez des representants de creuseurs et de dechireurs, de collecteurs et de racleurs, nous demontrons les effets de la qualite 3. Effect of de la nourriture sur le voltinisme, le rythme de croissance et la taille a la maturite. Pour les Is of mayfly predateurs, la qualite de la nourriture est uniformement haute, mais la quantite de nourriture (density des proies) influe evidemment sur leurs cycles biologiques. Un changement de regime, DEWALL. dherbivore a preclateur, ou une certaine absorption de tissus animaux aux stades ulterieurs s diminm is est une caracteristique du cycle biologique de plusieurs insectes aquatiques. 11 y a interaction ,chiedlicher de la temperature avec la qualiti aussi bier que la quantite de nourriture dans ses effets sur la 05-709. croissance, de meme quun effet direct sur le contrOle du metabolisme. Des etudes plus poussees am habitat sur le role de la nourriture dans les phenomenes du cycle biologique necessiteront des expe- s. Can. J. riences de laboratoire ou des etudes contrOlees sur le terrain afin de separer les effets de la temperature et de la nourriture. nd chronic Fish. Res. Received July 31, 1978 Recu le 31 juillet 1978 Accepted December 14, 1978 Accepte le 14 decembre 1978 in the egg ^ejdovsky) THE study of trophic relations in freshwater com- insects has been criticized (e.g. Resh 1976; Fuller and . 43: 719— munities reveals a bewildering array of foods available Stewart 1977). However, the partitioning of taxa on and methods of resource utilization. As Hynes (1970, the basis of food-acquiring mechanisms, that is, com- p. 192) suggested "It may seem inappropriate to con- munity functional role, rather than what is eaten, has sider the food of invertebrates in any biotope, as it is proven useful in approaching certain ecological ques- obviously as varied as the invertebrates themselves." tions (Cummins 1973, 1974; Merritt and Cummins Because of such complexity, it seems necessary to at- 1978; Wiggins and Mackay 1978). This approach, tempt some simplification in evaluating the general which stresses partitioning of food resources on a com- role of nutrition in controlling aquatic insect life his- munity basis, reveals that detrital utilization by tories — primarily growth (i.e. rate and maximum size shredders (coarse particle feeders) and collectors (fine attained). The stereotyping of food habits, based on particle feeders) dominates most forested headwater what is eaten, at the generic or family level for aquatic streams. This is in contrast to many terrestrial systems in which the insects feed primarily on living plant Paper presented at the Plenary Session of the 26th An- tissue. nual Meeting of the American Benthological Society held at Various aspects of food (diet) as a factor influencing Winnipeg, Man., May 10-12, 1978. life histories, or life history strategies, are examined. Technical Paper No. 4875, Oregon Agricultural Experi- ment Station, and Contribution No. 322 of the Coniferous Since field data implicating food as a causal factor Forest Biome, Ecosystems Analysis Studies, U.S. Interna- usually have other possible explanations, our task is tional Biological Program. akin to completing a jigsaw puzzle with most of the pieces missing. Furthermore, the interaction of abiotic Printed in Canada (J5334) factors, especially temperature, with food quality and Imprime au Canada (15334) quantity (food per unit of environment) confounds the 336 J. FISH. RES. BOARD CAN., VOL. 36, 1979 TEMPERATURE 25 tive correlation `■ Control of Control of of microbial flora Density per Density per nitrogen content Unit of Food Unit of Environment 20 and ATP conter Control of R. Speaker, and Animal I FOOD QUALITY 1 I FOOD QUANTITY I the rate of leaf di Metabolism fast; Carya, inter Nutritional Density of t° slow) is a gc Value per Unit Food Units 01 Food preference. C 10 3 C •- 3. Although s GROWTH I A conditioned subs Flo. 1. Relationship between temperature and food in the feeding rate to n control of macroinvertebrate growth. 5 FOOD QUALITY 0 problem (Fig. 1). A bias to lotic examples is evident magnifica both in the experimental data presented and literature Compared wi cited because our research programs are directed to FIG. 2. Life cycles of the wood gouger Heteroplectton Alnus leaves are stream studies. californicum and the leaf shredder Lepidostoma quercina, and one of the expressed as mean individual weight at each sample interval at Berry Creek, Benton Co., Oreg. Water temperature is vertebrates (lye Food Resources of Aquatic Insects given as mean monthly temperature. Cummins 1974; The range of organic materials potentially available fore, alder leave as foods for aquatic insects extends from the highly comparison in s refractory to the readily assimilable. The relative nutri- rates to provide sufficient assimilative gut contact with Trichoptera at Os tional gradient is perhaps: (1) wood; (2) terrestrial the microbial flora to meet the animals nutrient re- the limnephilid leaf litter; (3) fine particulate organic matter (FPOM); quirements; (3) supplemental feeding on higher qualit) entire larval stat (4) decomposing vascular hydrophytes and filamentous food (especially the periphyton film); or (4) some com- specimens, it be algae; (5) living algae, especially diatoms; and (6) bination of the above. tioned alder leav animal tissues. Considerable evidence has accumulated Examples of xylophages include the elmid beetle, growth. A diet it (e.g. Biirlocher and Kendrick 1973a, b) that the Lara avara, the calamoceratid caddisfly, Heteroplectron or enchytraeid v microbial flora associated with categories 1-4 is the californicum, the craneflies, Lipsothrix nigrilinea and enabled continue primary source of nutrition for aquatic insects. Monk L. fenderi, and midges of the genus Braila. Life cycle son 1976, 1978) (1976) demonstrated a weak cellulase activity in gut studies of the dipterans are incomplete. Lara avara and from the laboral extracts of several aquatic insects but found no cor- H. californicum both grow slowly; the former probably time was at lea relation between the occurrence of cellulase and the requires 3 yr or more to complete development and the than twice as h supplemented di abundance of cellulose in the diet. However, Tipula latter has a 2-yr life cycle. Microbial symbionts capable and other shredders have been shown to have hind gut of digesting cellulose have not been demonstrated in only 22.65 (-±1.1 symbionts that may be instrumental in the assimilation the hind guts of either species. compared with of products of cellulose degradation (Meitz 1975). The growth pattern of H. californicum is compared supplement. with that of a typical leaf shredder, Lepidostoma Laboratory-co quercina, in the same stream (Fig. 2). The major food with leaves Gougers and Shredders growth period for both species is from September to sibility that an These functional groups encompass those species that February when water temperature ranges from about laboratory-condi feed on coarse particulate organic matter (CPOM ) 12 to 4°C. Lepidostoma quercina is univoltine. with 2-3 wk at 12-1 (food categories 1 and 2) and reduce the particle size an instantaneous growth rate (IGR) of 2.7% • d-1, laboratory. Fec by chewing-gouging and mining wood, and skeletoniz- whereas H. californicum has a 2-yr cycle with an IGR stream-conditior ing leaf litter. Woody detritus, the most refractory of 0.9% •d-i. ditioned leaves material in aquatic habitats, has a processing time of The degradation of deciduous leaves by shredders has were more pal. at least decades. In water, microbial degradation of received considerable attention in the last decade and velopment to fift wood occurs largely on exposed surfaces (Anderson was recently reviewed by Anderson and Sedell (1979). on field-conditi and Sedell 1979). Initially food is available to in- From the viewpoint of dietary effects on life histories, ginally more ac vertebrates only through gouging at the surface, but some salient features of the shredder function are conditioned leav when tissue softens, the inner tissues are mined. Al- Life cycles of many shredders (e.g. Tipula and are not significt though wood debris offers an extremely nitrogen-poor many caddisflies) are keyed to the autumnal pulse of below the weigl diet (C to N ratio 300-500:1), in western coniferous leaf fall, with the major growth period occuring in the ment.