The nutritional status and ovarian development of Halyomorpha halys adults collected in an apple orchard and in coppiced trees were investigated in 2000 and 2001, and those of adults reared on apple trees with fruits were investigated in 2002. Adults were observed earlier in the apple orchard than in the coppices; adults immigrated into the apple orchard in May of each year. Female adults had developed ovaries and produced mature eggs. Adults were seldom observed in the orchard after early June, when many adults were observed in the coppices. However, many adults were observed in the apple orchard from mid-July to early August in 2001; the nutritional status of these adults was inferior to that of adults collected in the coppices, and many of the females had undeveloped ovaries. The nutritional status and the number of deposited eggs of the adults reared on apple trees with fruits were significantly inferior to those of adults reared on peanuts and soybeans, foods which were similarly suitable as mature fruit of Japanese flowering cherry. These results suggest that apple fruit is not as good a food for H. halys adults as other plants, but apple is satisfactory when more suitable foods are in short supply.
Nutritional status of post-overwintering adults of Halyomorpha halys at their hibernating site was investigated in Akita Prefecture, northern Japan from 2000 to 2005. Nutritional levels of the adults were significantly lower than those of pre-hibernating adults, and the fat body did not develop. Additionally, nutritional levels of the adults recently exited from the hibernating site were significantly lower than those of the adults at their hibernating site in April in 2001 and 2002. Almost all the adults given only water in field from late April could not survive until late May in 2002. These observations suggested that post-overwintering adults of H. halys exiting from the hibernating sites cannot survive for a long period, if they cannot feed on their suitable food plant.
Competitive displacement is considered the most severe consequence of interspecific competition; if a superior competitor invades the habitat of an inferior species, the inferior species will be displaced. Most displacements previously reported among arthropods were caused by exotic species. The lack of investigation of displacement among native species may be due to their apparently harmonious coexistence, even if it is equivalent to an outcome of interspecific association. A seasonal change in the species composition of spider mites, from Panonychus ulmi to Tetranychus urticae, is observed in apple trees worldwide. Previous laboratory experiments have revealed amensal effects of T. urticae on P. ulmi via their webs. Using manipulation experiments in an orchard, we tested whether this seasonal change in species composition occurred as the result of interspecific competition between these spider mites. Invasion by T. urticae prevented an increase in P. ulmi densities throughout the experimental periods. Degree of overlap relative to the independent distribution on a leaf-surface basis (omega (S)) changed from positive to negative with increasing density of T. urticae. T. urticae invasion drove P. ulmi toward upper leaf surfaces (competitor-free space). The niche adjustment by P. ulmi occurred between leaf surfaces but not among leaves. Our findings show that asymmetrical competition between T. urticae and P. ulmi plays an important role in this unidirectional displacement and that the existence of refuges within a leaf produces the apparently harmonious coexistence of the mites and obscures their negative association.
In order to improve the rearing efficiency of Halyomorpha halys, I developed a new rearing method using carrots with a peanut-soybean diet. Nymphs were reared under one of three food conditions, as follows: FC-A, raw peanuts and dry soybean seeds (a conventional rearing method); FC-B, carrot flesh only; and FC-C, carrot flesh, raw peanuts and dry soybean seeds. The adult emergence ratio of nymphs on FC-C was significantly higher than on FC-A, and was as high as on FC-B. The developmental period of nymphs fed FC-C was not significantly different from that of those fed FC-A, and was significantly shorter than those fed FC-B. The body size of adults fed FC-C was significantly greater than that fed FC-A, but that fed FC-B was significantly inferior to that of FC-A. The nutritional status of adults fed FC-C was not significantly different from that of those fed FC-A, and was significantly greater than those fed FC-B. The survival period and the number of eggs deposited by females fed FC-C were not significantly different from those fed FC-A, and were significantly greater than those fed FC-B. These results suggest that adding carrots to a peanutsoybean diet significantly improves the rearing of successive generations of H. halys.
To improve the success of integrated pest management (IPM) in apple orchards, we investigated whether generalist phytoseiid mites have suppressed the occurrence of Tetranychus urticae. In Akita Prefecture, northern Japan, in 2012 and 2013, two types of experimental plot were compared. Conservation plots had been managed for the conservation of generalist phytoseiid mites by selective chemical spraying without mowing since 2009. Conventional plots were managed by non-selective chemical spraying with regular mowing. The conservation plots had significantly fewer T. urticae adult females per tree in both years. Two species of generalist phytoseiid mites-Typhlodromus vulgaris and Amblyseius tsugawai-were continuously present in the conservation plots, with only a few T. urticae. The conservation plots had significantly more A. tsugawai adult females in the undergrowth in both years, and significantly more T. vulgaris adult females on apple leaves in 2012. Typhlodromus vulgaris was continuously present in the conservation plots but was scarce from late May to early August in the conventional plots. In the presence of T. vulgaris, low numbers of T. urticae did not increase on apple leaves. These results indicate that the generalist phytoseiid mites serve as important biological control agents in IPM in apple orchards.
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