Sensory Responses Of Three Scarab Beetles To Artificial Flowers And Castorbean Leaves

The larvae of scarabs(so-called “grub”)are a mostly distributed group of below-ground insect pests in Northern China,which damage most seriously on root system of various crops.Presently,the conventional control measures such as soil-treatment or seed-dressing have heavy negative effect on field eco-system and environment.Field-trapping of the scarab adults may be an important approach to implement the object of natural policy of “pesticide decreasing,chemical fertilizer decreasing,and yield increasing”,because the larvae are soil-inhabited and the adults fly actively above the ground.Previously,many info-chemical-based attractants have been reported in various scarab species.However,information about the response of these nocturnal scarab species to floral visual cues is relatively lack.The profoundly understanding of this issue will be helpful to develop effective traps being compatible with these ever-known attractants.In this dissertation,the role of floral visual cues was studied in both sexes of three scarab beetle species(Holotrichia oblita,H.parallela,and A.corpulenta).Flower patterns were designed using n-petal rose curve and radial gradient tools.The floral pattern includes plain colors,radial gradients,and petal petals.The two visual and olfactory sensory patterns are then prioritized by comparing the attractiveness of the corresponding preferred model with common olfactory information in each sex of each species.In the end,Choice frequency of the male and female adults of three scarab beetle species under the dual-choice conditions of castorbean leaf visual cue versus blank,castorbean leaf olfactory cue versus blank,and visual cue versus olfactory cue of castorbean leaf.The main results are as follows:(1)Under the condition of 8 plain colors four-petal flower patterns,both male and female of the H.oblita and H.parallela preferred yellow and white plain colors,irrespective of their sexes.In contrast,A.corpulenta showed significant gender differentiation.Specifically,the females of A.corpulenta mostly preferred the magenta color,followed by the white color,while the males showed no preference among 8 plain colors.(2)Under the condition of radial gradient pattern,the two sexes of H.oblita were different,and the highest frequencies of selection for females and males were yellow-white and white-yellow respectively.On the contrary,there was no difference between the two sexes of H.parallela,and the preferred color was yellow.The remarkable sexual differentiation was found in A.corpulenta regarding to the necessity of radial gradient treatment,the female preferred white-magenta,and the male preferred black-red.(3)According to the best pattern of each sex of each scarab species,the number of corolla fissures was designed to be the 4-,8-,and 12-petaled patterns and the trend response of the scarab species was studied.The results show the 4-petaled patterns were most preferred by all the test insects,regardless of their species and gender.(4)When visual cue(the corresponding optimal flower pattern pattern for each sex of each species)was compared with olfactory information(80 ?L benzyl acetate plus 120 ?L phenylacetaldehyde),the primary sensory modality was olfaction,irrespective of scarab species and sexes.There is a lot of information,so the three species of scarab beetle supposed to be active at night do not rely on olfactory information to search for host plants.(5)Choice frequency of the male and female adults of three scarab beetle species under the dual-choice conditions of castorbean leaf visual cue versus blank,castorbean leaf olfactory cue versus blank and visual cue versus olfactory cue of castorbean.The results show that the males of H.parallela reliy mainly on odor to search for castorbean leaves,whereas females rely on visual information as well as relying on olfactory information to search for castorbean.Both male and female adults of A.corpulenta are mainly dependent on odor to search for castorbean leaves.The male and female adults of H.oblita responded to the visual information of the castorbean,but the males responded to the smell information of the castorbean,but the female did not respond to the olfactory information of the castorbean.This shows that there are obvious differentiations between species and genders in the sensory channels used in the search of castorbean by the three scarab species.However,when the visual information and the olfactory information of castorbean were directly paired and tested,there was no significant difference in the frequency of the selection of the two types of information by all sexes of all species.