Tetsuo Gotoh

Cardinium symbionts cause cytoplasmic incompatibility in spider mites.

Intracellular symbiotic bacteria belonging to the Cytophaga–Flavobacterium–Bacteroides lineage have recently been described and are widely distributed in arthropod species. The newly discovered bacteria, named Cardinium sp, cause the expression of various reproductive alterations in their arthropod hosts, including cytoplasmic incompatibility (CI), induction of parthenogenesis and feminization of genetic males. We detected 16S ribosomal DNA sequences similar to those of Cardinium from seven populations of five spider mite species, suggesting a broad distribution of infection of Cardinium in spider mites. To clarify the effect of Cardinium on the reproductive traits of the infected spider mites, infected mites were crossed with uninfected mites for each population. In one of the populations, Eotetranychus suginamensis, CI was induced when infected males were crossed with uninfected females. The other six populations of four species showed no reproductive abnormalities in the F1 generation, but the possibility of CI effects in the F2 generation remains to be tested. One species of spider mite, Tetranychus pueraricola, harbored both Cardinium and Wolbachia, but these symbionts seemed to have no effect on the reproduction of the host, even when the host was infected independently with each symbiont.

Effect of temperature on life history of the predatory mite Amblyseius (Neoseiulus) californicus (Acari: Phytoseiidae).

Amblyseius (Neoseiulus) californicus is an indigenous mite in Japan that feeds on many spider mite species. We evaluated the development, survivorship and life-history parameters of A. californicus on a diet of eggs of Tetranychus urticae (red form). More than 97.3% of A. californicus eggs hatched and more than 81.6% of newly hatched larvae attained maturity at temperatures between 15 and 35 °C. Females oviposited at 37.5 °C, but no eggs hatched. At 40 °C, no females laid eggs. The lower threshold temperature from egg to oviposition was 10.3 °C and the thermal constant was 86.2 degree-days. Based on these data, the maximum number of generations that could complete development in a year under field conditions in Ibaraki, central Japan, would be between 21 and 28. At 25 °C, females laid a mean of 41.6 eggs during a mean oviposition period of 19.4 days. The intrinsic rates of natural increase (rm) were 0.173 at 20 °C, 0.274 at 25 °C and 0.340 at 30 °C.

Wolbachia distribution and cytoplasmic incompatibility based on a survey of 42 spider mite species (Acari: Tetranychidae) in Japan

Wolbachia are a group of maternally inherited bacteria that infect a wide range of arthropods. Wolbachia infections are known to result in the expression of various abnormal reproductive phenotypes, the best known being cytoplasmic incompatibility. The first systematic survey of 42 spider mite species in Japan revealed that seven species (16.7%) were infected with Wolbachia. Wolbachia in the spider mites were grouped into three subgroups in supergroup B by phylogenetic analyses of the wsp gene. Most spider mites did not show cytoplasmic incompatibility when infected males were crossed with uninfected females. However, all infected populations of Panonychus mori and Oligonychus gotohi (five and four populations, respectively) possessed modification-positive strains of Wolbachia, and the cytoplasmic incompatibility decreased egg hatchability and female ratio of the spider mites. Thus, some Wolbachia strains cause sex ratio distortion in their hosts.

Prevalence of Cardinium Bacteria in Planthoppers and Spider Mites and Taxonomic Revision of “Candidatus Cardinium hertigii” Based on Detection of a New Cardinium Group from Biting Midges

ABSTRACT Cardinium bacteria, members of the phylum Cytophaga-Flavobacterium-Bacteroides (CFB), are intracellular bacteria in arthropods that are capable of inducing reproductive abnormalities in their hosts, which include parasitic wasps, mites, and spiders. A high frequency of Cardinium infection was detected in planthoppers (27 out of 57 species were infected). A high frequency of Cardinium infection was also found in spider mites (9 out of 22 species were infected). Frequencies of double infection by Cardinium and Wolbachia bacteria (Alphaproteobacteria capable of manipulating reproduction of their hosts) were disproportionately high in planthoppers but not in spider mites. A new group of bacteria, phylogenetically closely related to but distinct from previously described Cardinium bacteria (based on 16S rRNA and gyrB genes) was found in 4 out of 25 species of Culicoides biting midges. These bacteria possessed a microfilament-like structure that is a morphological feature previously found in Cardinium and Paenicardinium. The bacteria close to the genus Cardinium consist of at least three groups, A, B, and C. Group A is present in various species of arthropods and was previously referred to as “Candidatus Cardinium hertigii,” group B is present in plant parasitic nematodes and was previously referred to as “Candidatus Paenicardinium endonii,” and group C is present in Culicoides biting midges. On the basis of morphological and molecular data, we propose that the nomenclature of these three groups be integrated into a single species, “Candidatus Cardinium hertigii.”

Spider Mites of Japan: Their Biology and Control

Spider mite biology and control in Japan were reviewed. Seventy-eight spider mite species of 16 genera (Family Tetranychidae) have been recorded in Japan. Several of the species recently described were separated from a species complex comprising strains with different ecological performance such as host range. These separations were first supported by crossing experiments and then confirmed by molecular genetic studies. Spider mite control in Japan is still dependent on heavy acaricide spraying in order to attain products of extremely high quality. The commercial use of natural enemies in spider mite management has just started.

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.

Synonymy between two spider mite species, Tetranychus kanzawai and T. hydrangeae (Acari: Tetranychidae), shown by ribosomal ITS2 sequences and cross-breeding experiments.

Amplification of the second internal transcribed spacer (ITS2) of ribosomal DNA was used to compare seven samples of the Tetranychus kanzawai Kishida-- T. hydrangeae Pritchard & Baker mite complex from five different countries: Australia, the Congo, Indonesia, Japan and the USA. No morphological differences were detected between these mites and their ITS2 sequences displayed strong similarity except for a small nucleotide divergence of 0.2% in specimens from Australia and Indonesia. Reciprocal crosses and backcrosses between mites assumed to be T. kanzawai and T. hydrangeae respectively showed reproductive compatibility. Fertile hybrid females were obtained in all cases, indicating conspecificity of the mites tested. It is concluded that T. hydrangeae is a synonym of T. kanzawai. The evidence suggests that T. kanzawai originated in South-east Asia and probably spread throughout the world on Hydrangea spp. cuttings.

Life-history traits of the acarophagous lady beetle, Stethorus japonicus at three constant temperatures

Stethorus japonicusKamiya (Coleoptera: Coccinellidae) is an indigenous ladybird beetle in Japan, which feeds on many spider mite species. We evaluated the development, survivorship and life-history parameters of this lady beetle on a diet of eggs of the two-spotted spider mite, Tetranychus urticae Koch (red form) (Acari: Tetranychidae). In addition, the effect of short photoperiod on its reproduction was assessed. Survival rates from egg to adult were more than 71% at temperatures between 17.5 and 30 °C. The highest immature mortality was 100% at 35 °C followed by 76% at 15 °C and 52% at 32.5 °C. The lower threshold temperature for development from egg to egg-laying adult was 13.0 °C and the thermal constant was calculated as 238.7° days. Based on these data, the maximum number of generations that could complete development in a year under field conditions in Ibaraki, central Japan, would be between five and seven. The intrinsic rates of natural increase (rm) were 0.093 at 20 °C, 0.156 at 25 °C and 0.241 at 30 °C. Reproductive diapause was induced at photoperiods with light phases shorter than 13 h at 18 °C.

Intraspecies Variation in the Kanzawa Spider Mite Differentially Affects Induced Defensive Response in Lima Bean Plants

The Kanzawa spider mite, Tetranychus kanzawai, is a polyphagous herbivore that feeds on various plant families, including the Leguminacae. Scars made by the mite on lima bean leaves (Phaseolus lunatus) were classified into two types: white and red. We obtained two strains of mites—“White” and “Red”—by selecting individual mites based on the color of the scars. Damage made by the Red strain induced the expression of genes for both basic chitinase, which was downstream of the jasmonic acid (JA) signaling pathway, and acidic chitinase, which was downstream of the salicylic acid (SA) signaling pathway. White strain mites also induced the expression of the basic chitinase gene in infested leaves but they only slightly induced the acidic chitinase gene. The Red genotype was dominant over the White for the induction of the acidic chitinase gene. The amount of endogenous salicylates in leaves increased significantly when infested by Red strain mites but did not increase when infested by White strain mites. JA and SA are known to be involved in the production of lima bean leaf volatiles induced by T. urticae. The blend of volatiles emitted from leaves infested by the Red strain were qualitatively different from those infested by the White strain, suggesting that the SA and JA signaling pathways are differently involved in the production of lima bean leaf volatiles induced by T. kanzawai of different strains.