Kazunori Ohashi

Identification of spider mites (Acari: Tetranychidae) by DNA sequences: A case study in northern Vietnam

Abstract Identification of spider mite species has been an important but complicated issue in pest control. We studied the species composition of spider mites collected in agricultural fields of northern Vietnam by using mitochondrial cytochrome oxidase subunit I sequences as a case study of the DNA barcoding identification technique for spider mites. Specimens were identified by comparing obtained DNA sequences with known sequences deposited in DNA databases. If phylogenetic analysis was used together, the DNA barcoding approach was useful for species identification of spider mites, especially for the genus Tetranychus. Using DNA barcoding, we classified most of the Vietnamese samples into Tetranychus kanzawai Kishida, T. urticae Koch and T. truncatus Ehara.

Thermal Microhabitat Use by the Ladybird Beetle, Coccinella septempunctata (Coleoptera: Coccinellidae), and Its Life Cycle Consequences

Abstract Most central Honshu populations of the ladybird beetle, Coccinella septempunctata L., pass the winter as quiescent adults. However, variations in life cycle within populations have been observed: hibernating and reproductive adults simultaneously coexist in the same habitat in winter. We studied microhabitat use patterns of this beetle in winter on a sunny slope of a southeast-facing riverbank. We found that, even though natural substrates were available, the beetle preferred to use artificial substrates such as metal cans (iron or aluminum), papers, and wooden materials discarded on the slope as oviposition and pupation sites. The artificial substrates were relatively easily warmed by solar radiation and were therefore used as thermal microhabitats by the beetle. Although ambient winter air temperatures of this region were not high enough for the beetles to complete their development, the use of thermal microhabitats enabled them to do so by thermal conduction. Prey aphids were also abundant during the winter. Thermal microhabitat use enables these beetles to complete an additional generation in winter.

Kanzawa spider mites acquire enemy‐free space on a detrimental host plant, oleander

Studies have proposed that predators of herbivores suffer significant fitness losses from the defense chemicals of host plants, and that herbivores adapted to these chemicals may experience reduced predation risk when residing on such plant species. We examined the effects of oleander, Nerium indicum Mill. (Apocynaceae), a host plant of the spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae), on their prime predator, Neoseiulus womersleyi (Schicha) (Acari: Phytoseiidae), and tested the hypothesis that this host plant provides enemy‐free space. At the study sites, T. kanzawai occurred on oleander shrubs; in contrast, although N. womersleyi was present in the area, no individuals were found on oleander. Tetranychus kanzawai feeding on oleander negatively affected the settlement, development, and egg production of N. womersleyi. The lower egg production was a result of both the direct effects of oleander and the indirect effects via T. kanzawai. Previous studies showed that the fitness of T. kanzawai in the presence of N. womersleyi was lower than that in the absence of the predator, and lower on oleander than on other palatable host plant species in the absence of predators. Our findings suggest that N. womersleyi may not be able to invade T. kanzawai patches on oleander shrubs, which results in the fitness of T. kanzawai being higher on oleander than on other host plant species in the same area when N. womersleyi is present. This supports the hypothesis that T. kanzawai acquires enemy‐free space on oleander using the direct and indirect adverse effects of oleander on their predators as major defense mechanisms.

Correction to dorsal setal lengths of spider mites (Acari: Tetranychidae: Schizotetranychus) from Malaysia described by Ehara.

Abstract Incorrect measurements of the dorsal body setae of four spider mites described as new in Ehara and Tho (1988) are corrected here. The species are Schizotetranychus kochummeni Ehara, S. approximatus Ehara, S. laevidorsatus Ehara and S. saitoi Ehara. In addition, the erroneous body size of S. saitoi described in the article is also corrected.