Yasuki Kitashima

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (rm) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the rm-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar rm-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.

Wolbachia-induced cytoplasmic incompatibility in Japanese populations of Tetranychus urticae (Acari: Tetranychidae)

Intracellular bacteria of the genus Wolbachia (alpha Proteobacteria) induce cytoplasmic incompatibility (CI) in many arthropod species, including spider mites, but not all Wolbachia cause CI. In spider mites CI becomes apparent by a reduced egg hatchability and a lower daughter:son ratio: CI in haplodiploid organisms in general was expected to produce all-male offspring or a male-biased sex ratio without any death of eggs. In a previous study of Japanese populations of Tetranychus urticae, two out of three green-form populations tested were infected with non-CI Wolbachia strains, whereas none of six red-form populations harbored Wolbachia. As the survey of Wolbachia infection in T. urticae is still fragmentary in Japan, we checked Wolbachia infection in thirty green-form populations and 29 red-form populations collected from a wide range of Japanese islands. For Wolbachia-infected populations, we tested the effects of Wolbachia on the reproductive traits and determined the phylogenetic relationships of the different strains of Wolbachia. All but one green-form populations were infected with Wolbachia and all strains belonged to the subgroup Ori when the wsp gene was used to determine the phylogenetic relationships of different strains of Wolbachia. Six out of 29 red-form populations harbored Wolbachia and the infected strains belonged to the subgroups Ori and Bugs. Twenty-four of 29 infected green-form populations and five of six infected red-form populations induced CI among the hosts. Thus, CI-Wolbachia strains are widespread in Japan, and no geographical trend was observed in the CI-Wolbachia. Although three red-form populations harbored other intracellular bacteria Cardinium, they did not affect host reproduction.

An LED-based UV-B irradiation system for tiny organisms: System description and demonstration experiment to determine the hatchability of eggs from four Tetranychus spider mite species from Okinawa.

We developed a computer-based system for controlling the photoperiod and irradiance of UV-B and white light from a 5×5 light-emitting diode (LED) matrix (100×100mm). In this system, the LED matrix was installed in each of four irradiation boxes and controlled by pulse-width modulators so that each box can independently emit UV-B and white light at irradiances of up to 1.5 and 4.0Wm(-2), respectively, or a combination of both light types. We used this system to examine the hatchabilities of the eggs of four Tetranychus spider mite species (T. urticae, T. kanzawai, T. piercei and T. okinawanus) collected from Okinawa Island under UV-B irradiation alone or simultaneous irradiation with white light for 12hd(-1) at 25°C. Although no eggs of any species hatched under the UV-B irradiation, even when the irradiance was as low as 0.02Wm(-2), the hatchabilities increased to >90% under simultaneous irradiation with 4.0Wm(-2) white light. At 0.06Wm(-2) UV-B, T. okinawanus eggs hatched (15% hatchability) under simultaneous irradiation with white light, whereas other species showed hatchabilities <1%. These results suggest that photolyases activated by white light may reduce UV-B-induced DNA damage in spider mite eggs and that the greater UV-B tolerance of T. okinawanus may explain its dominance on plants in seashore environments, which have a higher risk of exposure to reflected UV-B even on the undersurface of leaves. Our system will be useful for further examination of photophysiological responses of tiny organisms because of its ability to precisely control radiation conditions.

Life-history traits of the six Panonychus species from Japan (Acari: Tetranychidae).

Six species of the genus Panonychus are known from Japan. Life-history parameters of all six species were investigated at 25 °C, and for three species two strains of different geographical origin were included. The intrinsic rate of natural increase (rm) ranged from 0.172/day for the P. osmanthi albino strain to 0.209/day for P. citri, while the net reproductive rate (R0) varied from 23.98 in the thelytokous species P. thelytokus to 46.61 in P. citri. Both values were higher in the polyphagous species (P. ulmi, P. mori and P. citri), which are considered crop pests, than those in the oligophagous species (P. thelytokus and P. osmanthi), considered non-pests. The only exception was P. bambusicola, an oligophagous non-pest species with R0- and rm-values closely resembling those of the three polyphagous species.

Susceptibility to acaricides in nine strains of the tomato red spider mite Tetranychus evansi (Acari: Tetranychidae)

ABSTRACT The tomato red mite, Tetranychus evansi Baker and Pritchard, is a herbivore specialized on solanaceous plants, which has rapidly spread through the world during the last decade. It causes serious damage to a variety of crops in Africa and Europe but has not yet been reported to damage solanaceous crops in Japan. Tetranychus evansi is known to occur in Japan and it has the potential to become a severe pest on solanaceous crops here as well. The present study determined the susceptibility of nine T. evansi strains from various countries to 11 acaricides, because chemicals will be used as the first line of control against a new pest when it starts to cause severe damage to crops. Bifenazate, cyenopyrafen, milbemectin, spirodiclofen and tebufenpyrad showed higher toxicity – as indicated by 50% lethal concentrations (LC50) – for imagocidal action, and chlorfenapyr showed higher LC50 for ovicidal action in almost all T. evansi strains, compared with a susceptible strain of Tetranychus kanzawai Kishida. Still, the LC50 of imagocidal action of all acaricides, and for ovicidal action of all but one (cyflumetofen), on all nine strains tested was much lower than the recommended concentrations. These results suggest that mites from all nine strains could be controlled with acaricides as a first method, should they occur in high numbers on crops.

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species.

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O.×fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. TheP. osmanthi population was bimodal, with one peak in spring (May–June) and another in winter (November–January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak.

Susceptibility of the red spider mite, Oligonychus coffeae (Acari: Tetranychidae), to acaricides on tea plants in Japan

Abstract The red spider mite, Oligonychus coffeae (Nietner) (Tetranychidae), was recently found on mango and tea plants in the Ryukyu Islands, southern Japan. The susceptibility of adult females and eggs of a population from tea on Okinawa Island to 19 acaricides was examined, using a spray tower. The LC50 values in female adults of O. coffeae indicated high susceptibility to 15 acaricides and resistance only to chlorfenapyr. Of the group of 15 chemicals, bifenazate and fenbutatiaoxide yielded higher LC50 values in O. coffeae than in the susceptible strain of T. kanzawai, suggesting that these chemicals may be less effective in controlling O. coffeae. Eggs were resistant to ten acaricides, especially to bifenthrin and chlorfenapyr, but susceptible to the other nine. Thus, eggs were more resistant to the chemicals than adult females, but nine acaricides are candidates for effective control of O. coffeae.

Divergence in host range and reproductive compatibility in three strains of Oligonychus gotohi Ehara (Acari: Tetranychidae)

Abstract Preliminary observations indicated that Oligonychus gotohi Ehara collected from deciduous chestnut (deciduous-tree strain) could not develop on leaves of the evergreen broad-leaved tree Lithocarpus edulis (Makino) Nakai in the laboratory. Furthermore, we found an evergreen arrhenotokous (A) strain that produces both female and male progeny and an evergreen thelytokous (T) strain that produces only female progeny. These observations suggest that O. gotohi consists of either host races or sibling species. To determine which is the case, we examined the above three strains on 19 fagaceous plant species. The deciduous-tree strain successfully developed and oviposited on seven deciduous trees but did not develop on evergreen trees at all. The evergreen-A strain had the narrowest host range and could develop and oviposit only on three species of deciduous trees and only on three species of evergreen trees. The evergreen-T strain grew well on six deciduous trees and on all but one of the evergreen trees. Thus, the three strains demonstrated host plant divergence. Malate dehydrogenase (MDH) zymograms among populations of the same strain were similar, but those from the different strains were clearly different. Inter-population crosses in the deciduous-tree and the evergreen-A strains were compatible, but the reciprocal crosses between the deciduous-tree and the evergreen-A strains produced no females, indicating that these two strains were reproductively isolated. Neither virgin females of the evergreen-T strain nor evergreen-T strain females crossed with males of either the deciduous-tree or the evergreen-A strain produced male offspring. Thus, O. gotohi contains at least three different biological entities that may be sibling species.

Geographic variation of esterase and malate dehydrogenase allozymes in two spider mite species, Panonychus osmanthi and P. citri (Acari: Tetranychidae) in Japan

Abstract The genetic basis of malate dehydrogenase (MDH) and an esterase (α-Est 3) in the citrus red mite Panonychus citri (McGregor) and P. osmanthi Ehara and Gotoh was studied by polyacrylamide gel electrophoresis and crossing experiments. Based on the banding patterns and the phenotype-segregation ratio, the MDH-1 appeared as a dimeric enzyme of a single locus composed of three codominant alleles (S, M and F) in P. citri. Esterase (α-Est 3), also a dimeric enzyme regulated by two codominant alleles (S and F), was polymorphic in some populations of P. citri, and the frequency of the F allele was higher in southwestern populations than in other populations. The F allele of P. osmanthi, a mite that superficially resembles P. citri, was observed in only one population and all others were fixed for the S allele. At the MDH-1 locus, all populations of P. osmanthi and P. citri were fixed for the M allele with one exceptional population of P. citri. In this population, most females exhibited a single band of the ‘MM’ homozygote, but one female showed three bands of the ‘SM’ heterozygote and two females showed three bands of the ‘MF’ heterozygote. Thus, little geographical variation was found in allele distribution at the MDH-1 locus, but some variation was detected at the α-Est 3 locus only in P. citri.

A new species of the genus Bryobia Koch (Acari: Tetranychidae) from Iran

Abstract A new mite, Bryobia mirmoayedii n. sp. (Tetranychidae), is described and illustrated based on females, a male and larvae collected from the grass, Poa bulbosa L. (Poaceae), in Rijabin Kermanshah Province, Iran.