POPULATIONECOLOGY Effects of Host Diet on the Orientation, Development, and Subsequent Generations of the Gypsy Moth (Lepidoptera: Lymantriidae) Egg Parasitoid Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) RICHARD W. HOFSTETIER 1 ANDKENNETH F. RAFFA Department of Entomology, University of Wisconsin-Madison, 345 Russell Laboratories, 1630 Linden Drive, Madison, WI 53706 Environ. Entomol. 26(6): 1276-1282(1997) ABSTRACT Female Ooencyrtns ktlvanae (Howard) were attracted to odors from gypsy moth, Lymantria dispar (L.), egg masses in a 4-way olfactometer. Responses to egg mass odors varied with the difference of larval diet of the host. The number of gypsy moth generations on a particular larval diet also appeared to affect parasitoid orientation to the resulting egg masses. The plant species on which gypsy moth larvae fed affected characteristics of both the egg masses and the emerging wasps. Gypsy moth egg masses derived from plant-fed larvae had larger, but fewer, eggs than those derived from larvae fed artificial diet. The effects of host larval food on egg parasitoid emergence appeared in the 2nd generation, apparently because wasp develop- mental substrate affected their fecundity. O. ktlvanae that developed in eggs derived from oak-fed gypsy moths produced more offspring than those that developed in eggs derived from tamarack-fed gypsy moths, regardless of subsequent ovipositional substrate. The offspring sex ratio was influenced by the ovipositional and parental substrates. The proportion of females was highest in larval treatments and egg mass sections that yielded the largest eggs. O. kuvanae generally parasitized more eggs in the section of the egg mass that was laid first by the gypsy moth. KEY WORDS Ooencyrtm kuvanae, Lymantria dispar, egg parasitoid, host location, sex ratio, fecundity INSECTPARASITOroSLOCATEsuitable hosts by respond- ing to various stimuli from the host or host habitat (Price 1981, Turlings et al. 1990). Larval parasitoids often respond to plant volatiles such as those emit- ted in response to herbivore feeding (Alphen and Vet 1986). Likewise, host food plant can have strong effects on the size, sex ratio and development time of larval parasitoids (House 1977, Greenblatt and Barbosa 1981, Corrigan et al. 1991). Among egg parasitoids, however, the role of the host feeding substrate is less direct. Eggs are often separated from the larval host plant in both time and space (Brown et al. 1981, Rossiter 1981, Mauffete and Lechoweiz 1984), and therefore plant injury pro- vides a less reliable cue for host location. Egg parasitoids are more commonly reported to ex- ploit host and host derived by-products as primary kairomones (Lewis et al. 1972, Vinson 1976, Kai- noh et al. 1990). Host plants are known to affect indirectly the reproductive success of egg parasitoids, however. Type of host food plant can influence herbivore egg size (Rossiter 1987), which can directly affect para- 1 Current address: Yakima Agricultural Research Laboratory, USDA-ARS,Wapata,WA98951. sitoid offspring size and vigor (Bai et al. 1992). Parasitoid size may enhance adult competitiveness, dispersal ability, longevity, egg load, and overwin- tering success (Assen et al. 1989). Thus, there could be advantages for egg parasitoids of polyphagous herbivore hosts to orient toward eggs of those in- dividuals that feed on certain plant types or species. We know relatively little, however, about how larval feeding substrate affects the behavior and develop- ment of egg parasitoids. The gypsy moth, Lymantria dispar L., is the pri- mary host of the egg parasitoid Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae). Gypsy moths deposit eggs in 1 large mass, often away from the larval host plant. At high densities, female gypsy moth larvae are known to crawl up to 50 m to find a suitable pupation site, although most travel sub- stantially shorter distances (Lance and Barbosa 1982). Upon eclosion, the flightless females crawl upward a few centimeters to meters, where they mate and oviposit. Host plant diet directly influ- ences the number and size of gypsy moth eggs (e.g., Rossiter 1987). Ooencyrtus kuvanae populations are highly local- ized within forests and cluster on egg masses of particular trees and tree species (Rossiter 1981, 0046-225X/97/l276-1282$02.00/0 © 1997EntomologicalSociety of America Downloaded from https://academic.oup.com/ee/article/26/6/1276/2464423 by guest on 16 October 2021