Shoji Sonoda

Genotyping for the G4946E site of ryanodine receptor gene in Plutella xylostella (Lepidoptera: Yponomeutidae) considering gene duplication

Genotyping for the previously reported G4946E mutation site of the ryanodine receptor (RyR) gene was conducted individually in Plutella xylostella Linnaeus strains with different sensitivities to diamide insecticides. Results obtained by direct sequencing using primers previously reported for the mutation site were not indicative for the resistance status of the strains examined, possibly because of gene duplication. A typical example is that the RyR gene sequences with the G4946E mutation were found in the laboratory-susceptible strain. However, all clones with the G4946E mutation lacked introns, suggesting that the mutation encoded in intronless sequences does not function as a resistance factor. Primers exclusively amplifying the RyR gene sequences with introns were designed based on data obtained by cloning and nucleotide sequencing of RyR gene sequences amplified from 28 insects belonging to six strains. Using the primers, genotyping for the mutation site was conducted individually. Results showed that resistant strains contain more insets of resistant homozygote.

Cypermethrin resistance and reproductive types in onion thrips, Thrips tabaci (Thysanoptera: Thripidae)

Cypermethrin resistance and reproductive types were examined for T. tabaci strains. Some arrhenotokous and thelytokous strains encoded the sodium channel mutation (T929I) involved in cypermethrin resistance. However, the resistance levels varied to some degree among the strains. A cytochrome P450 inhibitor, piperonyl butoxide, showed different synergistic effects on the strains examined. These results suggest that fundamental and additional levels of cypermethrin resistance in T. tabaci are conferred respectively by reduced sensitivity of the sodium channel and by cytochrome P450-mediated detoxification.

Biotic performances of thelytokous and arrhenotokous strains of Thrips tabaci (Thysanoptera: Thripidae) showing resistance to cypermethrin

Two distinct reproductive types of Thrips tabaci Lindeman, one thelytokous and one arrhenotokous, have been shown to develop target-insensitive cypermethrin resistance conferred by sodium channel mutation (T929I). In this study, we examined the relation between cypermethrin resistance and biotic performances of these reproductive types. Among the T. tabaci strains examined, resistant arrhenotokous strains became adults more quickly after hatching than resistant thelytokous strains. Female adults of resistant thelytokous strains exhibited shorter longevity and oviposited fewer eggs than those of susceptible strains of the same reproductive type. Resistant arrhenotokous strains exhibited similar longevity and fecundity to susceptible thelytokous strains. We further examined the relation between reproductive types and T929I using a total of 85 strains. All 53 arrhenotokous strains encoding T929I were judged to be cypermethrin resistant. Among 32 thelytokous strains with T929I, only four were regarded as cypermethrin resistant. Based on the results, we discuss possible mechanisms accounting for the recent prominence of arrhenotoky T. tabaci in Japan.

Molecular evaluation of diamide resistance in diamondback moth (Lepidoptera: Yponomeutidae) populations using quantitative sequencing

A method to estimate proportions of the G4946E mutation in the ryanodine receptor gene, a major mechanism of diamide insecticide resistance, was developed for Plutella xylostella Linnaeus populations using quantitative sequencing (QS). Using the QS-based method, the relationship between proportions of the G4946E mutation and mortalities for diamide (flubendiamide) was examined using field-collected populations. Results showed that the populations might be classifiable as diamide resistant.

Utilization of plant food resources by phytoseiid mite species with different feeding habits

To examine the utilization of plant food resources by the phytoseiid mite species Amblyseius eharai Amitai & Swirski, Euseius sojaensis (Ehara), and Neoseiulus californicus (McGregor) (Acarina: Phytoseiidae), we collected phytoseiid mites on peach leaves in Japanese peach orchards. Then, phytoseiid mite samples that had been estimated to contain a single phytoseiid mite species using quantitative sequencing were selected. Simultaneously, we surveyed pollen available for phytoseiid mites in peach orchards and selected Digitaria ciliaris (Retz.) Koeler (Poales: Poaceae), Eleusine indica (L.) Gaertn. (Poales: Poaceae), and Pinus densiflora Siebold & Zucc. (Pinales: Pinaceae) as pollen source plants. Subsequently, the internal transcribed spacer sequences of ribosomal genes or the non-coding region of the chloroplast DNA of the three plant species were amplified from phytoseiid mite samples using polymerase chain reaction. Results showed that phytoseiid mite species with different feeding habits use plant food sources, possibly pollens, of D. ciliaris and P. densiflora.

Clonal variation of sexual morph production in response to temperature and photoperiod in soybean aphid, Aphis glycines (Hemiptera: Aphididae)

The life cycle of Aphis glycines Matsumura (Hemiptera: Aphididae) has been recognized as holocyclic. This study examined photoperiod and temperature effects on fecundity and sexual morph production using six A. glycines clones collected in northern, eastern, western, and southern Japan. Results showed that the six clones included anholocyclic and intermediate ones. Low temperature and short photoperiod negatively affected fecundity, except for one clone with anholocyclic life cycle. Possible mechanisms for the year-round parthenogenetic production of the anholocyclic clone are discussed.

Seasonal proportion change of ryanodine receptor mutation (G4946E) in diamondback moth populations

This study examined the seasonal proportion change of ryanodine receptor mutation (G4946E) for Plutella xylostella populations using quantitative sequencing. Results showed that the proportions of G4946E generally increased from spring through summer, but then decreased in autumn. Furthermore, the proportions in late autumn were similar to those in early spring of the subsequent year. These results suggest that diamide effectiveness for P. xylostella control in the reference year can be evaluated based on a proportion survey in the prior year.