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Inter- and intra-specific host discrimination in gregarious and solitary endoparasitoid wasps
No full textIn nature, most species of Lepidoptera are attacked by parasitoids, and some species may be hosts for several parasitoid species. When hosts are parasitized by more than one female of the same species (=superparasitism) or females of different species (=multiparasitism), then intrinsic competition occurs for control of host resources. To reduce competition, some parasitoids are able to recognize the difference between parasitized and unparasitized hosts. Inter- and intra-specific host discrimination were investigated in the two sympatric species, the gregarious Cotesia kariyai (Watanabe) and solitary Meteorus pulchricornis (Wesmael), endoparasitoids of the Oriental armyworm Mythimna separata (Walker). To measure host discrimination, choice experiments were conducted in which females of both species foraged and chose between healthy host larvae and hosts initially parasitized by either C. kariyai or M. pulchricornis. An olfactory test was also performed to examine the discrimination behavior of the two parasitoids. Our results showed that, in oviposition choice tests, both braconid female wasps were able to discriminate between unparasitized hosts and from four to seven day-old hosts previously attacked by conspecific and heterospecific wasps. On the other hand, superparasitism and multiparasitism occurred even in host larvae that were parasitized two days earlier. However, once the immature parasitoids hosts are at larval stage (1st and 2nd instar), super- and multiparasitism were avoided in the two-choice test, but the latter often occurred in the multiple-choice experiment. Host discrimination abilities may have been based on plant volatile signals incurred from damaged plants and internal mechanisms from four to seven post-parasitized hosts.
Microcystins derived from lysing Microcystis cells do not cause negative effects on crustacean zooplankton in Lake Taihu, China
No full textMicrocystins (MCs) have a toxic effect on crustacean zooplankton in the laboratory, but there is little or no unequivocal evidence in the literature of their lethal effects on crustacean zooplankton in the field. We used the natural microcystins extracted from Microcystis spp. to test if they could cause any negative effects on crustacean zooplankton. We conducted three experiments in enclosures with water from Lake Taihu, China, and microcystins derived by extraction from Microcystis spp. collected from the lake when the species was in bloom conditions. Initial concentrations of extracellular microcystins (EMCs = MC-RR + MC-LR + MC-YR) ranged from 9.7 to 44.9 μg/L in treatments with microcystin addition. Microcystin concentrations sharply decreased on second day in all the three experiments. EMCs at the end of the experiments varied from only 2.7 to 14.2 % of the levels at the start of the experiments. The dominant species of crustacean zooplankton in the lake were Bosmina longirotris, Ceriodaphnia cornuta, Mesocyclops spp., Limnoithona sinensis, Sinocalanus dorrii and Schmackeria inopinus. ANOVA analysis showed that the density and biomass of cladoceran and copepod did not significantly differ between treatments with microcystin addition and controls. Our results indicate that microcystins derived from lysing Microcystis do not cause any negative effects on crustacean zooplankton.
