Ecological and Evolutionary Consequences of Variation in Clutch Size in Asteromyia Carbonifera (o.s.) (Diptera: Cecidomyiidae)

Weis, Arthur Edward

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Description

Title

Ecological and Evolutionary Consequences of Variation in Clutch Size in Asteromyia Carbonifera (o.s.) (Diptera: Cecidomyiidae)

Author(s)

Weis, Arthur Edward

Issue Date

1981

Department of Study

Entomology

Discipline

Entomology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Biology, Ecology

Language

eng

Abstract

• The gall-midge Asteromyia carbonifera induces blister-like galls on the leaves of Canadian goldenrod, Solidago canadensis (Compositae). Female midges deposit one to five offspring per gall. During their brief adult existence, females produce a number of galls. The number of eggs laid at each ovipositional site is termed the "clutch size." Midge larvae are potential hosts to five species of hymenopterous parasitoids. Three aspects of the plant/gall-maker/parasitoid community are examined in light of current theories in evolutionary ecology: (1) the selective pressures that act upon the midge to determine optimal clutch size, (2) patterns of resource utilization among the parasitoid species, particularly as affected by gall developmental progress and midge clutch size, and (3) demonstration that ovipositional success by the parasitoid Torymus capite is influenced by gall size as affect by midge clutch size.
• A. carbonifera exhibits a semelparous life history, however its reproductive tactics are more complex than the "big bang" strategy that is often associated with semelparity. Its life history entails precocious maturation of gametes followed by a brief adult existence consisting of many ovipositional events. Females can be selected to deposit eggs in many small clutches or a few large ones. Optimal clutch size in this species is determined by a balance between the fitness per offspring, as determined by the size of clutch into which it is placed, and the number of clutches a mother can expect to deposit in her brief adult existence. It was found that as clutch size increased, so did competition between sibs within a gall, with the result that larvae developing in large clutches were smaller and less fecund than those developing in small clutches. Egg to adult survival was affected by parasitoid attack which was heavier on smaller clutches. Positive effects of small clutch size outweighed the deficits, thus, offspring from clutches of one enjoy the greatest potential fitness. If mothers could be expected to live to deposit all their eggs, the clutch size of one would be favored. However, a model is presented which indicates that as probability of mortality between each ovipositional event increases the likelihood of depositing all eggs decreases. As the between-site survivorship decreases, optimal clutch size increases.
• The parasitoid species attacking the gall-midge Asteromyia carbonifera (O.S.) were studied to determine (1) the trophic relationships with the host and with one another, (2) the temporal sequence in which they attack, and (3) the way in which they respond to the naturally occurring variation in the number of host larvae per gall. All five species feed parasitically upon the host larva. Torymus capite also feeds upon previously parasitized hosts, on gall tissue, and, as an adult, drinks haemolymph from the host larva. By feeding on hosts already parasitized by Tetrastichus fumipennis, T. capite may depress population levels of the former. The parasitoids attack in the following sequence: Platygaster solidaginis, T. fumipennis, T. capite and Tetrastichus tesserus. Time of attack by the species is related to their abilities to penetrate gall tissues during various phases in gall development. The species, T. fumipennis, T. capite and T. tesserus, showed no aggregative response toward variation in the number of host larvae per gall.
• Laboratory studies examined the mechanisms that lead to greater ovipositional success by Torymus capite in galls containing large clutches. Gall size increases subproportionally with clutch size. Thus in galls containing large clutches, midge larvae lie closer to the gall's outer margin and thus are more often within the reach of T. capite's ovipositor. Despite their greater accessability, midge larvae in large clutches often go unutilized. Features of this host/parasitoid system suggest that T. capite may employ the "hunting by expectation" foraging strategy.

Graduation Semester

1981

Type of Resource

text

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