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The oriental fruit fly, Bactrocera dorsalis(Hendel), is a devastating pest of citrus fruits. After successful mating, adult females insert their eggs into the ripened fruit, resulting in moldy and rotten fruit and causing great economic losses for the citrus industry. In the field, flies initiate copulatory behaviors as twilight approaches, and decreasing light intensity in this period is the normal stimulus for copulation. In this study, ten light intensities ranging from 0–30 000 lux were set to identify the typical intensity that strongly regulates the copulation behavior of B. dorsalis. Three light intensities found to regulate the copulation behavior were then selected to verify their effects on adult male wing fanning and female chemotaxis towards 2,3,5-trimethylpyrazine (TMP). At last, strong light and complete darkness were artificially combined in the lab to verify whether they could prevent copulation to inform behavioral manipulation of oriental flies in the future. The results indicated that adult flies generally initiated copulatory behaviors at low light intensity (<1 000 lux). Stronger light significantly prevented copulation in proportion to intensity, with nearly no copulation events initiated when light intensity was above 20 000 lux. Both male wing fanning and female chemotaxis towards TMP were attenuated as light intensity became stronger. However, at 10 000 lux, males still fanned their wings to a certain extent while TMP completely lost its attractiveness to females. In the darkness, adults did not initiate any sexual behaviors, e.g., copulation, wing fanning, or chemotaxis to TMP. One hour of strong light (10 000 lux) combined with continuous darkness completely prevented mating. These results show that light condition is an essential factor for copulatory behaviors in the oriental fruit fly. Researchers could thus manipulate light conditions artificially or disrupt the molecular target in flies' light transduction pathway to develop environmentally-friendly techniques to control this pest.

‘CandidatusLiberibacter asiaticus (CLas)’, which causes citrus Huanglongbing (HLB) disease, has not been successfully cultured in vitroto date. Here, a rapid multiplication system for CLas was established through in vitroregeneration of axillary buds from CLas-infected ‘Changyecheng’ sweet orange (Citrus sinensisOsbeck). Stem segments with a single axillary bud were cultured in vitroto allow CLas to multiply in the regenerating axillary buds. A high CLas titer was detected in the regenerated shoots on an optimized medium at 30 days after germination (DAG). This titer was 28.2-fold higher than in the midribs from CLas-infected trees growing in the greenhouse. To minimize contamination during in vitroregeneration, CLas-infected axillary buds were micrografted onto seedlings of ‘Changyecheng’ sweet orange and cultured in a liquid medium. In this culture, the titers of CLas in regenerated shoots rapidly increased from 7.5×104to 1.4×108cells μg–1of citrus DNA during the first 40 DAG. The percentages of shoots with >1×108CLas cells μg–1DNA were 30 and 40% at 30 and 40 DAG, respectively. Direct tissue blot immunoassay (DTBIA) indicated that the distribution of CLas was much more uniform in regenerated plantlets than in CLas-infected trees growing in the greenhouse. The disease symptoms in the plantlets were die-back, stunted growth, leaf necrosis/yellowing, and defoliation. The death rate of the plantlets was 82.0% at 60 DAG. Our results show that CLas can effectively multiply in citrus plantlests in vitro. This method will be useful for studying plant-HLB interactions and for rapid screening of therapeutic compounds against CLas in citrus.

Heavy metal contamination has been regarded as an environmental variable that affects the efficiency of pest biological control, but the parasitic fitness of parasitoids under heavy metal stress is poorly understood. Herein, the effect of Cd exposure through the host pupa of Hyphantria cuneaon the parasitic fitness of Chouioia cuneawas investigated, and the mechanism by which Cd exposure affects the interaction between H. cuneaand C. cuneafrom the perspective of innate immunity in host insect and the oxidative status in the parasitoid offspring was explored. Our results indicated that Cd can be transferred from the H. cuneapupae to the parasitoid offspring, and the transfer coefficient reflected biological amplification. There were no significant differences in the rates of parasitism success and offspring emergence between the untreated and Cd-treated groups. However, after parasitizing Cd-accumulated pupae, the parasitic fitness of offspring wasps (e.g., the number, individual size and life span) decreased significantly. Under Cd exposure, the cellular and humoral immunity of H. cuneapupae decreased significantly. Compared with the untreated group, the H2O2content of parasitoid offspring in the Cd-treated group was significantly increased. Cd exposure significantly inhibited superoxide dismutase activity in parasitoid offspring, but the contents of ascorbic acid and glutathione were significantly increased by Cd stress. Taken together, these results indicate that Cd exposure reduces the cyclic utilization efficiency of C. cuneaon H. cuneapupae. The oxidative status of parasitoid offspring triggered by Cd exposure could be responsible for the reduced parasitic fitness of C. cuneaon Cd-accumulated H. cuneapupae.