No abstract

The nonmigratory grasshopper Oedaleus infernalis Saussure (Orthoptera : Acridoidea) is an agricultural pest to crops and forage grasses over a wide natural geographical distribution in China. The genetic diversity and genetic variation among 10 geographically separated populations of O. infernalis was assessed using polymerase chain reaction-based molecular markers, including the intersimple sequence repeat and mitochondrial cytochrome oxidase sequences. A high level of genetic diversity was detected among these populations from the intersimple sequence repeat (H: 0.2628, I: 0.4129, Hs: 0.2130) and cytochrome oxidase analyses (Hd: 0.653). There was no obvious geographical structure based on an unweighted pair group method analysis and median-joining network. The values of FST, θII, and Gst estimated in this study are low, and the gene flow is high (Nm > 4). Analysis of the molecular variance suggested that most of the genetic variation occurs within populations, whereas only a small variation takes place between populations. No significant correlation was found between the genetic distance and geographical distance. Overall, our results suggest that the geographical distance plays an unimpeded role in the gene flow among O. infernalis populations.

No abstract

The entomopathogenic nematodes (EPN), together with their symbiotic bacteria, are obligate and lethal parasites of insects and are applied as biological approaches to pest management. In this paper, we isolated 122 strains of symbiotic bacteria from 23 EPN isolates that were gathered in various soils containing different vegetations from different regions of China. All these isolated bacterial strains showed oral insecticidal activity and/or growth inhibition to the larvae of Ostrinia furnacalis. Among these strains, Xenorhabdus sp. SY5 exhibited high insecticidal activity to O. furnacalis, Plutella xylostella, Mythimna separata, Laphygma exigua and Tenebrio molitor, all of which are important agricultural pests. Xenorhabdus sp. SY5 was isolated from EPN Steinernema sp. SY5. Through DEAE-52 column chromatography, seven toxins were purified from X. sp. SY5. Bioassay results showed that all seven toxins had, to a certain extent, insecticidal activity and/or growth inhibition to O. furnacalis, T. molitor, P. xylostella, M. separata and L. exigua. Our data also showed that each of these toxins had different insecticidal activity and/or growth inhibition against different insect species. The partial toxin gene sequence of X. sp. SY5 was determined, and its deduced amino acid sequence only showed 75, 66 and 65% identities to homologues of EPN symbiotic bacteria Photorhabdus luminescens, Xenorhabdus nematophila and Yersinia mollaretii, respectively. These results suggested that strain SY5 is a highly virulent EPN symbiotic bacterial strain that has a potential value for biological pest control.

Many studies have demonstrated that many species of parasitoid wasps can control offspring sex ratio in response to environmental variables. This article tests the effects of temperature, relative humidity, photoperiod, foundress number, foundress age, host number, interval time of host supplying, species of food, species of host and symbiotic bacterium (Wolbachia) on sex ratio of Trichogramma ostriniae. Results showed that the sex ratio of T. ostriniae was affected significantly by temperature (35°C), number of foundress (>2 number), age of foundress (3-day-old) and Wolbachia. Through transmitted Wolbachia from Trichogramma embryophagum to Trichogramma dendrolimi, even the reproductive mode of T. dendrolimi was changed from gamogenesis to thelytoky. Our work verifies the sex ratio theory and implies that the potential effectiveness of Trichogramma spp. as a biological control agent can be further improved.