Suitability of Listronotus maculicollis (Coleoptera : Curculionidae) as a host for Microctonus hyperodae (Hymenoptera : Braconidae)

Microctonus hyperodae Loan is an effective parasitoid against Listronotus b onariensis (Kuschel) in New Zealand. To determine the potential for M. hype rodae as a biological control agent for L, maculicollis Dietz, live specime ns were imported to a quarantine facility in New Zealand. A series of exper iments examined the suitability of 3 South American geographic populations (ecotypes) of M. hyperodae in terms(of parasitism rates, prepupal emergence , and development times compared with the natural host, L. bonariensis. Lim ited development occurred in L.. maculicollis by all 3 ecotypes, but parasi tism rate was significantly lower than in L. bonariensis. Comparison with a related parasitoid showed higher rates of prepupal emergence from L. macul icollis for M. aethiopoides Loan than for M. hyperodae. The presence of ann ual bluegrass, Poa annua, in the test arena and prior experience on L. macu licollis increased parasitism rate significantly when a combination of L. m aculicollis and L. bonariensis were exposed to M hyperodae. The low rate of successful prepupal emergence by M. hyperodae in L. maculicollis was attri buted in part to a physiological response by L. maculicollis which led to e ncapsulation of the developing parasitoid egg and larva. Based on these res ults, M. hyperodae probably would not be a suitable biological control agen t of L. maculicollis in the United States because of the low rates of paras itism observed under laboratory conditions and delayed development times co mpared with those in the natural host, L. bonariensis. M. aethiopoides is m ore successful in parasitizing and developing in L. maculicollis, but this parasitoid also exhibited significantly lower levels of parasitism compared with L. bonariensis, although development times were comparable. Furthermo re, M. aethiopoides used in these trials probably originated in North Afric a and may not be suited to a northeastern United States climate.