【Aim】 In view of the strong adaptability of Periplaneta americana in harsh environments, this study aims to isolate and screen actinomycetes with antibacterial activity from the gut of P. americana adults in the wild in Dali prefecture of Yunnan province so as to provide strain resources for the development of antibiotics. 【Methods】 The gut actinomycetes of P. americana adults were isolated by coating plate method and plate marking method, and six strains of common human pathogenic bacteria, Staphylococcus aureus, methicillin-resistant S. aureus, Pseudomonas aeruginosa, Enterococcus faecalis, Escherichia coli and Salmonella typhimurium, were used as the indicator strains. The antibacterial activities of the secondary metabolites extracted from these actinomycetes were determined by the Oxford cup method. The actinomycetes with broad spectrum and obvious antibacterial activities were identified according to their morphological features as well as 16S rRNA gene sequence analysis. Their taxonomic statuses were confirmed by the BLAST analysis of their 16S rRNA gene sequences and phylogenetic analysis. 【Results】 Totally, 41 actinomycetes strains were isolated from the gut of P. americana adults. The results of antibacterial activity test showed that 34 strains (82.9%) of actinomycetes had inhibitory activities against at least one indicator pathogenic bacterium. Among them, seven strains had inhibitory activities against more than three pathogenic bacteria, and nine strains had obvious antibacterial activities. Based on the results of phylogenetic analysis, these actinomycetes were identified as Streptomyces spp. 【Conclusion】 The gut of P. americana adults in the wild contains rich actinomycete resources with antibacterial activity, which provides an important microbial source for further exploration of new antibiotics.

 【Aim】 The objective of this study is to investigate the preference of Anoplophora chinensis to volatiles of Salix ohsidare in different physiological states, and to further explore the reasons for the difference in behavioral choice of A. chinensis between insect-infested and healthy S. ohsidare. 【Methods】 The volatiles of S. ohsidare twigs in the two physiological states (insect-infested and healthy S. ohsidare) were collected, respectively, by using the dynamic headspace adsorption method, and then the collected volatile samples were identified and analyzed by gas chromatography-mass spectrometry (GC-MS). The electrophysiological and behavioral responses of A. chinensis to standard compounds of the main compounds identified from the volatile samples were analyzed by electroantennogram (EAG) and Y-tube olfactometer, respectively, and the trapping efficacies of single volatile compound and the two-component and three-component formulae of volatile compounds on A. chinensis adults were analyzed by large cage behavior experiment and field trapping test. 【Results】 We identified three main compounds from the volatiles of healthy S. ohsidare twigs, including α-pinene, 3-carene and camphor, and five main compounds from the volatiles of insect-infested S. ohsidare, including α-pinene, β-pinene, 3-carene, β-ocimene and camphor. In addition, the amphor content in the volatiles of insect-infested S. ohsidare twigs was significantly higher than that in the volatiles of healthy S. ohsidare twigs, the 3-carene contents in both the volatiles of insect-infested and healthy S. ohsidare twigs were not significantly different, while the α-pinene content in the volatiles of healthy S. ohsidare twigs was significantly higher than that in the volatiles of insect-infested S. ohsidare twigs. The EAG experiment showed that the relative EAG response value of A. chinensis adults to three compounds, α-pinene, 3-carene and β-ocimene, were relatively high, and gradually increased with the increase of the concentrations of these three compounds. The relative EAG response values of A. chinensis adults to β-pinene and camphor exhibited no significant difference, and the concentration changes of these two compounds had no significant effect on the relative EAG response value. The Y-tube olfactometer experiment showed that α-pinene, 3-carene and β-ocimene at the concentration of 1 mg/mL all attracted significantly more male adults of A. chinensis than the control group (paraffin oil), 1 mg/mL β-ocimene also attracted significantly more female adults than the control group, and 3-carene at the concentration of 10 mg/mL attracted significantly more male adults than the control group. The large cage behavior experiment exhibited that the insect-infested formula D of three components (α-pinene∶3-carene∶β-ocimene=42∶30∶103), α-pinene and β-ocimene attracted the largest number of A. chinensis adults, which was significantly higher than the numbers of A. chinensis adults attracted by the healthy formula H of two components (α-pinene∶3-carene=105∶38) and 3-carene. The field trapping test showed that α-pinene and the insect-infested formula D had the best trapping efficacies on A. chinensis adults, with the number of adults trapped significantly higher than those trapped by β-ocimene and the healthy formula H, while 3-carene and the blank control group did not trap any A. chinensis adults. 【Conclusion】 α-Pinene shared in the volatiles of insect-infested and healthy S. ohsidare twigs and β-ocimene specific in insect-infested S. ohsidare twigs are the two important host plant volatile compounds with the attractiveness to A. chinensis adults, while 3-carene inhibits the attractiveness of α-pinene to A. chinensis adults. We speculate that β-ocimene specific in the volatiles of insect-infested S. ohsidare is one of the causes that insect-infested S. ohsidare is more susceptible to the damage of A. chinensis than healthy S. ohsidare.

【Aim】 The parasitism rate of Aphidius gifuensis on Myzus persicae is quite high. Therefore, it is widely used for A. gifuensis to control M. persicae in tobacco. However, in the process of artificial propagation of A. gifuensis certain environmental factors may have influences on its growth and development. This study aims to make clear of the effects of photoperiod, humidity and temperature on the parasitism of A. gifuensis on M. persicae. 【Methods】 The parasitism rates on M. persicae nymphs and the emergence rates, longevity, sex ratios (proportions of females) and metathoracic tibial lengths of A. gifuensis adults under the conditions of the temperature of 25℃ and the relative humidity of 70% combined with four photoperiods (9L∶15D, 12L∶12D, 14L∶10D and 19L∶5D), under the conditions of the temperature of 25℃ and the photoperiod of 14L∶10D combined with four relative humidity levels (65%, 70%, 75% and 80%), and under the conditions of the relative humidity of 70% and the photoperiod of 14L∶10D combined with four temperatures (10℃, 15℃, 25℃ and 35℃), respectively, were investigated in the laboratory. 【Results】 The results showed that the growth and development of A. gifuensis were negatively affected by too long or too short photophase. Under the temperature of 25℃ and the relative humidity of 70%, the body size of A. gifuensis adults under the photoperiod of 14L∶10D was the largest, with their metathoracic tibial length under this photoperiod the longest (0.439 mm), while their body size under the photoperiod of 12L∶12D was the smallest, with their metathoracic tibial length the shortest (0.345 mm). Under the temperature of 25℃ and the relative humidity of 70%, A. gifuensis adults under the photoperiod of 14L∶10D had the highest parasitism rate and longevity on M. persicae nymphs, which were 42.61% and 42.33 h, respectively. Under the temperature of 25℃ and the photoperiod of 14L∶10D, the parasitism rates of A. gifuensis adults on M. persicae nymphs increased at first and then decreased with the increase of relative humidity. Under the temperature of 25℃ and the photoperiod of 14L∶10D, the parasitism rate of A. gifuensis adults on M. persicae nymphs under the relative humidity of 75% was the highest (54.44%), while that under the relative humidity of 65% was the lowest (only 21.67%), the longevity and metathoracic tibial length of A. gifuensis adults under the relative humidity of 70% were the longest (42.33 h and 0.439 mm, respectively), while their longevity under the relative humidity of 75% was the shortest (only 20.42 h), and their metathoracic tibial length under the relative humidity of 65% was the smallest (only 0.373 mm). Under the relative humidity of 70% and the photoperiod of 14L∶10D, the temperature of 25℃ was more beneficial to the growth and development of A. gifuensis adults than 10℃ or 15℃, and the parasitism rate of A. gifuensis adults on M. persicae nymphs, and the proportion of females and metathoracic tibial length of A. gifuensis adults at 25℃ were 42.61%, 39.04% and 0.439 mm, respectively, higher than those at 10℃ and 15℃. However, the high temperature of 35℃ was not conducive to the parasitic behavior of A. gifuensis adults on M. persicae nymphs: Under this high temperature, no mummy aphid was found, and even the host aphids were all killed. 【Conclusion】 Under the temperature of 25℃ and the relative humidity of 70%, the photoperiod of 14L∶10D is more beneficial to improve the parasitism rate, body size and longevity of A. gifuensis adults. Under the temperature of 25℃ and the photoperiod of 14L∶10D, the humidity of 75% is more beneficial to improve the parasitism rate of A. gifuensis adults, while the humidity of 70% is more beneficial to the increase of their longevity and body size. Under the photoperiod of 14L∶10D and the relative humidity of 70%, the temperature of 25℃ is more conducive to the increase of their parasitism rate, body size and proportion of females, while the low temperature of 10℃ is more beneficial to prolong their longevity. The results of this study provide scientific references for the artificial propagation and rejuvenation of A. gifuensis in field greenhouses or indoor sheds.

 As the most successful biological pesticide, Bacillus thuringiensis (Bt) insecticide has been used to control pests in agricultural production for about 80 years. The wide and successful use of Bt insecticide due to its specificity, safety and efficiency has greatly reduced the application rate of chemical pesticides, making a huge contribution to environmental protection. However, due to long-term application, some target insect pests have gradually developed resistance to Bt. In this article, the research advances in insect humoral immunity and the mechanisms of Bt resistance in insects were summarized. Previous studies suggested that the blockage of toxin activation and/or the mutation or reduction of toxin receptor are the main causes of the development of Bt resistance in insect pests. However, in recent years, more and more studies have shown that Bt resistance in insects is also associated to their immune system, especially to humoral immune pathways such as Toll, IMD and proPO-AS. Therefore, we reviewed and inferred the main pathways in which the humoral immune system is involved in the development of Bt resistance in insects. The IMD immune pathway may be involved in regulating Bt resistance in insects through the MAPK signaling pathway, or insects may counteract sepsis caused by the destruction of midgut tissue by Bt through multiple immune responses and promote midgut tissue healing through the JNK signaling pathway, thereby increasing their resistance to Bt. Research with the humoral immune system as the breakthrough point could be a new direction for further exploring the mechanisms of Bt resistance in insects.