Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Interspecific competition between two scelionid egg parasitoids, the non-native, invasive Trissolcus basalis (Wollaston) and the native Trissolcus mitsukurii (Ashmead) on the southern green stink bug Nezara viridula (Linnaeus) in Japan.

Abstract

We compared the life history characteristics of two egg parasitoids: Trissolcus basalis (Wollaston) (TB), a non-native, invasive species, and the native Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) (TM) using the southern green sting bug Nezara viridula (Linnaeus) (Heteroptera: Pentatomidae) as a host, and analyzed effects of the interspecific competition between the two species. Observations of the color of parasitized egg masses of N. viridula indicate that the larval period of TM was shorter, but the developmental duration until adult emergence of TB was shorter than that of TM. Rapid growing of TM larvae is advantageous for survival in competition with TB larvae as confirmed by multiparasitism experiments. Further, TM does not have enough time to oviposit because adult female of TM shows strong aggressiveness against other TM individuals (and also against other species including TB) when multiple females oviposit in a host egg mass simultaneously, resulting in TM spending more time to oviposit. In contrast, TB can parasitize together with several other females of TB in a shorter period because it is less aggressive than TM. Interspecific competition between TB and TM when trying to oviposit in a host egg mass at different ratios of females (1:1 and 1:2) resulted in producing TM species in most emerged wasps, but TB emergence success was lower: 5.8% in 1:1, 23.4% in 1:2 ratios. The life span of TB females was about 90 days and that of TM was 60 days when inexperienced in oviposition, and the life spans of TB and TM with oviposition experience were about 48 and 23 days respectively, showing that TB females have a longer life than TM, regardless of oviposition experience. Total number of eggs laid during its lifetime was about 258 in TB and the female ratio was 0.48 (♀/(♂ + ♀)), while lifetime egg oviposition of TM was about 125 with 0.77 female ratio. About 21% of the TB wasps emerged successfully under dry conditions (20-30% humidity), but the TM could not emerge at all. Multiparasitism is reproductively disadvantageous for TB. However, these results suggest that TB has a greater ability to adapt to low humidity environments as well as complete the oviposition process more rapidly and produce more offspring because of its long adult life span and high fecundity when a large number of host egg masses are available due to its high relative host density.