The pederin-producing bacteria density dynamics in Paederus fuscipes at different developmental stages.

Pederin, a defensive toxin in Paederus fuscipes, is produced by an uncultured Gram-negative symbiont, which establishes a stable symbiotic relationship with a female host before completion of metamorphosis. However, the transmission process of pederin-producing bacteria (PPB) in P. fuscipes at different life stages remains unknown. Herein, the PPB population dynamics and transcriptome atlas for P. fuscipes development (egg, first-instar larva, second-instar larva, pupa, and newly emerged female and male) were characterised. We found that a microbial layer containing PPB covered the eggshell, which could be sterilised by smearing the eggshell with streptomycin. Maternal secretions over the eggshell are likely the main PPB acquisition route for P. fuscipes offspring. The PPB density in eggs was significantly higher than that in other life stages (p < 0.05), which demonstrated that the beetle mothers gave more PPB than the larvae acquired. Physiological changes (hatching and eclosion) led to a decreased PPB density in P. fuscipes. Pattern recognition receptors related to Gram-negative bacteria recognition were identified from P. fuscipes transcriptomes across various life stages, which might be used to screen genes involved in PPB regulation. These results will help advance future efforts to determine the molecular mechanisms of PPB colonisation of P. fuscipes.

Stable composition of gut microbiome in the Asian ladybeetle Coccinella septempunctata reared on natural and artificial diets.

The Asian ladybeetle, Coccinella septempunctata, is an important insect of predatory natural enemy, which has a strong control effect and application prospects for aphids, whiteflies, mealybugs, and other small-sized pests of agriculture and forestry crops. Gut microbiota composition posed impacts on development of insects. In order to clarify the effect of artificial feed feeding on the intestinal microbial species and structure of C. septempunctata, we compared the intestinal microbial flora of C. septempunctata reared on bean aphids and artificial food for 15 days. Results show that Proteobacteria was the dominant component in all groups at phylum level, Rhodobacter, Methylovigula, Burkholderia, and Bradyrhizobium were the dominant bacteria among all groups at genus level. As to the differences in bacterial community structure and diversity, there is no significant difference between Shannon index and Simpson index, the principal components analysis of the bacterial communities, and the samples were roughly distributed in different regions. After 15 days of feeding, artificial diet did not significantly reduce the microbial diversity of the gut of C. septempunctata compared to the aphid group, and there was no significant effect on the abundance of dominant flora in the gut of C. septempunctata, C. septempunctata gut has a similar core microbiota. This study clarifies the effects in intestinal microbial diversity and composition structure of the C. septempunctata with artificial diet, and provides a theoretical basis for understanding the intestinal microorganisms and optimizating the artificial diet of C. septempunctata.

Effects of Juvenile Hormone Analog and Days after Emergence on the Reproduction of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae) Populations.

Mythimna separata (Walker) is a main cereal crop pest that causes extensive damage to the world grain production. The effects of juvenile hormone on M. separata populations remain poorly understood. Here, we explored how JH analog (JHA) affected reproductive traits of both migrant and resident populations in this pest. Our results showed that the influence of JHA treatment on reproduction depended on adult age (days after emergence) of exposure to JHA and populations. Exposure of M. separata residents to JHA (methoprene) on day 1 and day 2 after adult emergence significantly shortened the pre-oviposition period, but increased the lifetime fecundity, mating frequency and grade of ovarian development compared to the controls. However, M. separata migrants exposed to JHA only on day 1 facilitated their reproduction, resulting in a reduction in the pre-oviposition period but an increase in lifetime fecundity, mating frequency and grade of ovarian development. In addition, exposure to JHA from day 2 to day 4 did not significantly affect the ovarian and reproductive development in both migrant and resident populations. These results indicated that the first two days after adult emergence were the sensitive period for residents. In contrast, only the first day after adult emergence was the sensitive stage for migrants. Our findings will contribute to a better understanding of JHA function on M. separata populations.

[Effects of neighbors with different sexuality and soil sterilization on biomass of Populus cathayana seedlings]. / 不同性别邻体和土壤灭菌对青杨幼苗生物量的影响.

Although plant-plant interactions have been intensively studied, few studies examined sex-related neighbor interactions in dioecious plant species. Here, we investigated the sexual diffe-rences in biomass accumulation, and analyzed the sexual neighbor effects and yields of sexual combination in Populus cathayana seedlings under the treatments of inter- and intra-sex neighbors and soil sterilization. The results showed that biomass accumulation of P. cathayana decreased in both of sexes when grown with an intra-sex neighbor. Females increased biomass accumulation under non-sterilization condition when grown with an inter-sex neighbor. Soil sterilization decreased biomass accumulation in both sexes of these plants, especially for females. Soil sterilization treatments did not significantly affect intra-sex interactions, but neutralized the positive effects in females and led the effects in males to turn from neutral to negative in inter-sex neighbors. The highest biomass in female-male combination under non-sterilization condition and the lowest biomass in male-male combination under sterilization condition were observed among combinations. These results indicated that the growth of female and male P. cathayana differed in their responses to their sexual neighbors, and that such neighbor effects were affected by soil microorganism. Our results could contribute to improve the productivity of poplar plantations in silviculture.

[Resistance realized heritability and risk assessment of Panonychus citri to avermectin and fenpropathrin].

On the basis of resistance breeding and selection in laboratory, and by using the threshold trait analysis in quantitative genetics, this paper studied the realized resistance heritability of Panonychus citri (McGregor) collected from Beibei of Chongqing to avermectin and fenpropathrin, and predicted the resistance risk of P. citri to these two acaricides. After 11- and 16-generations of selection with avermectin and fenpropathrin, the resistance of P. citri to the two acaricides increased by 3.8- and 29.9-fold, and the realized resistance heritability was 0.0475 and 0.1544, respectively. Under laboratory condition, to develop a 10-fold increase of resistance required 12-26 generations of selection for avermectin, and 7-16 generations of selection for fenpropathrin under the selection pressure of 50%-90% mortality for each generation. Under field condition, it would require more generations to develop the same resistance level. Comparing with bioacaricide avermectin, pyrethroid fenpropathrin had obviously higher resistance risk to P. citri. The results provided references for the resistance management of P. citri to acaricides.