Research On Host Plant Preference And Distribution Projection Of Ophraella Communa (Coleoptera: Chrysomelidae), A Biological Control Agent Of Common Ragweed

Introduction of natural enemies is an effective approach to the management of alien invasive weeds. A serious of challenges facing biological control practitioners and theoretician is how to accurately assess potential ecological risks of introducing biological control agents to non-target plants, so as to avoid new biological invasions with biocontrol. Ophraella communa LeSage (Coleoptera:Chrysomelidae), by origin of North America, was recently reported heavily attacking alien invasive ragweed, Ambrosia artemissiifolia (Compositae) in the mainland China. Because of not strictly monophagous, its potential risks to non-target plants are of great concern. In this paper, a series of experiments was carried out to study oviposition selection of O. communa by using both classic methods and their modifications in choice- and non-choice experiments in the laboratory and the field. The study has provided rich evidences for assessment of potential risks of O. communa to non-target plants, and useful knowledge for improvement of biological weed control practices. The following results were obtained.1. Ovipositon preferences of O. communa under indoor conditionsThe recognition time concept was used, and the time until plants were oviposited was fitted by the Cox proportional hazard model, to analyze the potential risks of oviposition as affected by feeding experiences and aging. The non-target plants for the test were A. trifida, X. sibiricum, two varieties of Helianthus annuus, and H. tuberosus, all in tribe Heliantheae of Composite. The experiments revealed a strong preference for the target weed A. artemisiifolia to the non-target test plants, but did not find significant influences of feeding experiences and aging on the preference. 2. Ovipositon preferences of O. communa under manipulated outdoor conditionsBehavioral phenomena have the potential to impact on the interpretation of test results obtained in laboratory. Thus, experiments were conducted both in a large walk-in cage in the field and in open field to observe oviposition preferences. The study showed that:(ⅰ) O. communa strongly preferred A. artemisiifolia for oviposition to non-target plants; (ⅱ) O. communa turned to A. trifida and X. sibiricum for oviposition without the presence of A. artemisiifolia, while the other non-target plants were at little risk.3. Oviposition selection of O. communa under in the open fieldA survey was made to investigate oviposition selection of O. communa for A. artemisiifolia as affected by various characteristics of host plants. Following characters were surveyed on a regular time interval and plots:plant height, plant patch size, shading, blooming, and damage levels. The factors surveyed were fitted as covariates with generalised linear mixed modeling (GLMM) to determine the major factors influencing the oviposition selection. The results showed that plant patch size, damage level and blooming have significanltly influences on oviposition selection of O. communa, while lighting and plant height, had no significanltly influences by their own. But there covariates had significanltly influences, by two-way interactions, on oviposition selection of O. communa, except the interaction between patch size and plant height.4. Oviposition strategy of O. communa for different plantsComponents of host quality (such as carbon, nitrogen and defensive metabolites) can affect potential and realized fecundity as well as oviposition strategy involving clutch size, egg size and quality in herbivorous insects. Both clutch and egg size of O. communa were greater on A. artemisiifolia than on the other non-target plants without trade-offs. However, a trade-off was detected between clutch size and egg size on X. sibiricum and H. annuus, where there was a negative linear relationship between clutch size and egg size, which suggested an oviposition strategy of either "many-small" or "a few-large".5. Oviposition strategy of O. communa for A. artemisiifoliaResource density and quality of host plant can affect oviposition strategy of herbivorous insects. Experiments were conducted to observe oviposition strategy of O. communa with different host-density patches. The results showed that the quality of host plants influenced oviposition strategy of O. communa, but the density did not. The strategy of oviposition was "many-large" at the early stage, but a trade-off between clutch size and egg size at the middle stage, and "few-small" at the later stage of oviposition. O. communa preferred A. artemisiifolia at the growing stage by laying larger egg-clutches (20.3±1.5 eggs) and egg size (0.077±0.001mm3) to the plants at seedling and flowering stages. O. communa laid a smaller clutch on the plant infected with egg-masses at lower proportion levels (0%,25%, 50% of leaves) than with the higher (75%,100%), and clutch size decreased linearly with egg-mass proportion on the plant that was exposed to oviposition. O. communa laid smaller eggs on the plant with 25% leaves infected with egg-masses than with the other egg-mass treatments, and a U-shaped curve was fitted between egg size laid and egg-mass proportion treated. The plants with lower levels of egg-mass infection (0%,25%) ran a higher hazard to be oviposited than those with higher levels O. communa laid a smaller clutch (<11.2 eggs) on the plant infected with higher levels of larvae (50%～100%) than with lower levels of larva infection (>21.6 eggs), a negative linear relationship between clutch size and larval infection proportion.O. communa laid smaller eggs (0.068±0.001 mm5) on the plant with 25% infection of larvae than on plants with the other treatments (> 0.077 mm3), and a positive linear relationship between egg size and larval infection was detected. The results suggest that O. communa performed oviposition trade-offs between egg number size on A. artemisiifolia as affected by egg- or larva-infection levels at the time of oviposition.6. Feeding preferences of O. communa adults and larvaeDeprivation of host plants can change feeding preferences of herbivorous insects. Experiments were conducted to study effects of starvationon feeding preferences of O. communa adults among different test plants. Feeding preferences of O. communa larvae among different test plants were also observed. The study showed that:(ⅰ) there were no significant differences in starvation time and survival rate between female and male; (ⅱ) except for the 48h starvation treatment, the other starvation treatments significantly affected host preferences of O. communa adults. (ⅲ) there were no significant differences in feeding choices as measured by feeding incidences (frequencies) between A. artemisiifolia and X. sibiricum in O. communa larvae, but there were significant differences as measured by the recognition time. However, there were significant differences as measured by both feeding choice frequencies and recognition time bewteen H. annuus and A. artemisiifolia, and X. sibiricum. 7. A projection of potential distribution of O. communa in mainland China.To assess the potential establishment of O. communa in mainland China, the CLIMEX software was used to predict potential habitats of the leafbeetle, its host A. artemisiifolia, and potential host plants, A. trifida and Helianthus annuus. The Bioclimatic Risk Index (BCRI), derived from the Ecoclimate Index (EI) in output of the CLIMEX analysis, was used to measure the probability of overlapping distribution between the leafbeetle and plant. The results show that O. communa has the potential to establish at locations from Shengyang, Liaoning Province in the north, through to Hainan province in the south of China, while east China, south China, and the east in southwest China, are potential suitable areas for its establishment. Suitable areas up to the north shared by O. communa and A. artemisiifolia border on Jinan, Shangdong province, while those shared by O. communa and A. trifida and H. annuus border on Shengyang, Liaoning Province. Suitable areas shared by the leafbeetle and all three plants lies in east and south China, and the eastern part in southwest China. The plantation of sunflower crop in north China is at low risk of feeding damage by O. communa.