Takayuki Mitsunaga

Larval Cannibalism and Intraguild Predation Between the Introduced Green Lacewing, Chrysoperla carnea, and the Indigenous Trash-Carrying Green Lacewing, Mallada desjardinsi (Neuroptera: Chrysopidae), as a Case Study of Potential Nontarget Effect Assessment

Abstract To study the potential competitive risk of the introduced Chrysoperla carnea (Stephens) on the indigenous trash-carrying chrysopid Mallada desjardinsi (Navás), we studied the occurrence of cannibalism and intraguild predation (IGP) at different prey densities. In C. carnea, 100% cannibalism was observed in the absence of aphids. In M. desjardinsi, cannibalism was also observed, but absence of cannibalism occurred at 35% in pairs of second- + third-instar larvae and at 70% in pairs of third- + third-instar larvae. In pairs of M. desjardinsi larvae whose trash package had been artificially removed, all third-instar larvae ate second-instar larvae. The trash package may play a role in the reduced mortality of younger larvae by cannibalism. IGP occurred in all pairs. In the absence of aphids, the interaction was symmetric between second-instar larvae, but asymmetric for second- versus third- and third- versus third-instar larvae, and the interaction was similar when M. desjardinsi larvae with or without trash package were paired with C. carnea larvae. When third-instar larvae of both species were paired, C. carnea larvae ate significantly greater numbers of M. desjardinsi larvae than vice versa. The trash package of M. desjardinsi larvae may thus not play a defensive role against IGP by C. carnea. Increasing the availability of aphids tended to decrease both cannibalism and IGP levels. Nontarget effects such as competitive displacement resulting in loss of potentially beneficial attributes of the indigenous M. desjardinsi by the exotic C. carnea are likely to be negligible under conditions of abundant aphids.

Time allocation of Orius sauteri in attacking Thrips palmi on an eggplant leaf

Orius sauteri (Poppius) (Heteroptera: Anthocoridae) is a polyphagous predator used as a biological control agent of palm thrips, Thrips palmi (Karny) (Thysanoptera: Thripidae). We studied O. sauteris searching efficiency, time allocation on a leaf, leaving tendency, and attacking of prey. Approximately 78% of the encountered prey was eaten. Searching for prey was concentrated for 86% of the time on the lower leaf side, where palm thrips are usually found. Patch residence times on empty leaves were different from those on leaves with T. palmi larvae. Walking activity was not affected by the thrips density, and walking took place during 64% of the total search time. The leaving tendency of O. sauteri was affected by the time from patch entry and the presence or absence of palm thrips, but not by the thrips density. If prey were present, the leaving tendency decreased (multiplication factor 0.327), resulting in longer giving‐up times than when no prey was present. The fact that the leaving tendency increases when patch exploitation lasts longer suggests that not much time is wasted on patches where encounters with prey are scarce.

Laboratory Hybridization Between the Introduced and the Indigenous Green Lacewings (Neuroptera: Chrysopidae: Chrysoperla) in Japan

Abstract We report on laboratory hybridization between the indigenous Chrysoperla nipponensis and its close relative, C. carnea, which has been imported since 2001 from Germany to Japan as a biological control agent. Interspecific hybrids were obtained, and fully viable and fertile F1 and F2 generations were produced. Crosses between C. carnea females and C. nipponensis males showed 41.3% fertility, but the reciprocal cross showed only 9.5% fertility. Despite the low fertility of interspecific crosses, most F1 hybrids were fertile and were successfully backcrossed to both parental species. However, F1 males from C. carnea females × C. nipponensis males showed low fertility (zero except for 20% in one case) when crossed with any females (F1 or backcross). In the one combination resulting in 20% fertility, an extremely long preoviposition period was observed, caused presumably by a mating delay. The absence of change in hatchability, adult emergence rate, total developmental period, or deviation from the 50:50 sex ratio from parents to the F2 generation of hybrids suggests that there is no genetic incompatibility between C. carnea and C. nipponensis resulting from hybrid breakdown. Because the courtship songs of the introduced C. carnea and the indigenous C. nipponensis are quite different, interspecific mating between the two close relatives may not occur under natural conditions. It will be necessary to monitor the establishment of the introduced C. carnea and its possible hybrids with the indigenous C. nipponensis in the wild to minimize any irreversible ecological risks, such as loss of genetic identity.

Two Year Field Study to Evaluate the Efficacy of Mamestra brassicae Nucleopolyhedrovirus Combined with Proteins Derived from Xestia c-nigrum Granulovirus

Japan has only three registered baculovirus biopesticides despite its long history of studies on insect viruses. High production cost is one of the main hindrances for practical use of baculoviruses. Enhancement of insecticidal effect is one possible way to overcome this problem, so there have been many attempts to develop additives for baculoviruses. We found that alkaline soluble proteins of capsules (GVPs) of Xestia c-nigrum granulovirus can increase infectivity of some viruses including Mamestra brassicae nucleopolyhedrovirus (MabrNPV), and previously reported that MabrNPV mixed with GVPs was highly infectious to three important noctuid pests of vegetables in the following order, Helicoverpa armigera, M. brassicae, and Autographa nigrisigna. In this study, small-plot experiments were performed to assess concentrations of MabrNPV and GVPs at three cabbage fields and a broccoli field for the control of M. brassicae. In the first experiment, addition of GVPs (10 µg/mL) to MabrNPV at 106 OBs/mL resulted in a significant increase in NPV infection (from 53% to 66%). In the second experiment, the enhancing effect of GVP on NPV infection was confirmed at 10-times lower concentrations of MabrNPV. In the third and fourth experiments, a 50% reduction in GVPs (from 10 µg/mL to 5 µg/mL) did not result in a lowering of infectivity of the formulations containing MabrNPV at 105 OBs/mL. These results indicate that GVPs are promising additives for virus insecticides.