Host pots were used to assess parasitism by A. columbi and were created according to the procedure described in Cronin and Strong (1990). Three to four female and two male adult planthoppers were placed in a 50-mm long by 26-mm diameter tubular clip cage that was positioned at the base of a single leaf of a potted cordgrass stem (16 cm diameter pots, 3–5 stems/pot). The planthoppers were given 48 h to lay eggs, during which time they produced a discrete host-egg clutch with an average (± 1 SE) of 64.4 ± 1.8 eggs (n = 257). By using experimentally created egg clutches, I minimized the variation in host age, density per leaf, and distribution of hosts within a leaf. Also, variation in cordgrass plant quality, which may influence parasitism (e.g., Price 1986), was minimized by using plants propagated under identical conditions.
Trap pots were used to estimate the density of adult A. columbi at each location within the patch and matrix. For each trap pot, a thin layer of Tanglefoot (The Tanglefoot Company, Grand Rapids, Michigan, USA) was applied to the basal 10 cm of 2 opposite-facing leaves of a host-free cordgrass stem. As I have found with the congeneric parasitoid A. sophiae (Cronin and Strong 1993a), female A. columbi do not detect the Tanglefoot, and readily walk onto or alight on the sticky leaves (Cronin 2003). Laboratory studies support the notion that these trap leaves represent independent replicates for the estimation of A. columbi numbers per leaf. Female wasps usually emigrate from a leaf by flying (Cronin 2003). Colonization of a subsequent leaf that is attached to the same or a different stem (~ 0.3 m away) occurs with equal likelihood. The distance moved is on the order of a few decimeters and is comparable to the movement patterns of A. sophiae (Cronin and Strong 1993a,b, 1999).
Cronin, J. T. 2003. Patch structure, oviposition behavior, and the distribution of parasitism risk. Ecological Monographs 73:283–300.
Cronin, J. T., and D. R. Strong. 1990. Biology of Anagrus delicatus (Hymenoptera: Mymaridae), an egg parasitoid of Prokelisia marginata (Homoptera: Delphacidae). Annals of the Entomological Society of America 83:846–854.
Cronin, J. T., and D. R. Strong. 1993a. Substantially submaximal oviposition rates by a mymarid egg parasitoid in the laboratory and field. Ecology 74:1813–1825.
Cronin, J. T., and D. R. Strong. 1993b. Superparasitism and mutual interference in the egg parasitoid Anagrus delicatus (Hymenoptera: Mymaridae). Ecological Entomology 18:293–302.
Cronin, J. T., and D. R. Strong. 1999. Dispersal-dependent oviposition and the aggregation of parasitism. American Naturalist 154:23–36.
Price, P. W. 1986. Ecological aspects of host plant resistance and biological control interactions among three trophic levels. Pages 11-20 in D. J. Boethel and R. D. Eikenbarry, editors. Interactions of plant resistance and parasitoids and predators of insects. Wiley and Sons, New York, New York, USA.