Comparative Nutritional Ecology Of Exotic Ophraella Communa (Coleoptera: Chrysomelidae)

Ophraella communa (Coleoptera: Chrysomelidae) of North American origin is a recently recovered exotic herbivorous insect in China mainland. It has been known that its host plants are limited to a few closely related plants in Heliantheae, Compositae, among which Ambrosia artemisiifolia is its dominant host plant in the field. It also occasionally attacks Xanthium canadense. In order to predict its potential risks to plants other than the target weed A. artemisiifolia, we conducted a comparative study on the nutritional ecology of this insect on plants that are closely related to its main host plant. We studied the insect in food consumption, utilization, food nutrition, and digestive enzyme activities.1. Consumption and utilization of food by O. communa larva and adults fed on A. artemisiifoliaThe survivorship of O. communa larvae was observed when fed on top (and tender) and lower (and tough) leaves of A. artemisiifolia plant. Consumption and utilization of larvae and adults at different ages were measured. The accumulative mortality of larvae fed on lower leaves on the stem was significantly higher than that on top leaves but not different from that on middle leaves on the stem. Fresh body weight of larvae increased markedly prior to age 6 day and then leveled off. The approximate digestibility (AD) was high (>80%) across all larval ages. AD declined with age before 10 days old and then increased. The common inverse relationship between AD and the efficiency of conversion of digested food (ECD) was not detected, probably owing to their base on 24h measurements. Relative rates, such as relative consumption rate (RCR), relative growth rate (RGR) and relative metabolic rate (RMR), were higher for early larvae than for later larvae. Consumption of adults under 4-day old was greater than older adults.2. Consumption and utilization of food by O. communa larva fed on different food plantsIn this study we measured food consumption and nutrition utilization of O. communa larvae fed on seven food plants. The 3rd instar larvae had less consumption on A. artemisiifolia and Xanthium sibiricum than on other test plants, A. trifid, Helianthus tuberosus, H. multiflorus, and two varieties of H. annuus, but had higher relative growth rate and utilization. Different aged larvae fed on same plant varied in consumption and utilization. The two-day old L3 larvae consumed more, but utilized less, than the one-day old, which produced the similar body weight increment. The consumption in fresh leaf weight and body weight obviously correlated with water content of food plant. Although consumption and utilization of larvae varied on different test plants, complete larval development could be realized on these plants.3. Relationship between nutritional indices of food plants and larval food consumptionThe measurement was made on Chlorophy C, soluble sugar, soluble protein, and water content in seven food plants, Ambrosia artemisiifolia, A. trifid, Xanthium canaden, Helianthus tuberosus, H. multiflorus, and two varieties of H. annuus. Analysis was conducted on correlation between nutritional components on one side and food consumption and body weight increment on other side. No correlation was detected between Chlorophy C and food use parameters, whereas a certain correlation was found between soluble sugar, soluble protein, and water content on one side and body weight and food consumption on other side.4. Digestive enzyme activity of O. communa larva fed on different food plantsDigestive enzyme activity is of importance for digestion functioning, and therefore for growth and development rates in insects. Amylase activity in larvae fed on A.artemisiifolia declined gradually with larval growth, but the activity of Trehalas increased gradually with larval growth. The reason for this pattern is that larval growth at different ages required different substances for metabolism. Activity of Trehalas in larvae fed on A. artemisiifolia and X. canaden was higher than fed on the other plants. The activity of CarE was higher in larvae fed on A. artemisiifolia, X. canaden, Helianthus plants than that in larvae fed on H. tuberosus and A. trifid.