Evaluation of mortality of Galerucella calmariensis L. (Coleoptera: Chrysomelidae) preimaginal life stages and pupal survival at two wetlands in Iowa

To quantify mortality of Galerucella calmariensis L. preimaginal life stages in wetlands, with influences levels of biological control of purple loosestrife, Lythrum salicaria L., we sampled G. calmariensis for 19 wk during 2004 in two Iowa wetlands. At each site, we randomly collected 15 to 19 L. salicaria stems that were either surrounded by water or not surrounded by water for a total of 30 stems per site on each sample date. At each site, partial life tables were constructed for egg, first instar, and second-third instars. Stem location (surrounded by water and not surrounded by water) did not affect mortality from egg to second-third instar, thus data were pooled to create a partial life table for each site. At Site 1, insect predators (Coccinellidae) were present on 16% of the sampled dates and at Site 2 insect predators (Coccinellidae and Chrysopidae) were present on 11% of the sampled dates. Mortality from egg to second-third instar was over 99% at both sites. Using the same L. salicaria stems collected for the partial life table, we longitudinally sliced the L. salicaria stems, to determine the pupation site of G. calmariensis within L. salicaria stems surrounded by water. Eighty-six pupae were collected within stems of L. salicaria plants surrounded by water from Site 1. No pupae were found within stems of L. salicaria in dry areas or from Site 2. This is the first report of G. calmariensis pupating within L. salicaria stems. In a laboratory study, three soil moisture treatments (0, 30, and 60% soil moisture) were used to determine soil moisture effects on G. calmariensis eclosion. No eclosion was observed from the 60% treatment. Eighty-four percent of adults eclosed from the 30% soil moisture treatment compared to 56% in the 0% treatment. The number of days (4) to eclosion was similar in the 0 and 30% soil moisture treatments. Abiotic and biotic factors affect G. calmariensis mortality and levels of biological control may vary relative to these factors.