Larval Host Preference Of Five Species Of Scarab Bettles

Scarabaeoidea is a large superfamily of Coleoptera,commonly called scarab beetles as adults,and white grubs as larvae.The Scarabaeoidea are usually considered as pests for their larval stage damaging plant roots underground.The pest management of Scarabaeoidea faces great difficulties,because of their edaphic living habits and complex feeding habits.With respect to a polyphagous pest,host preference is a main aspect of their living habits,and plays a key role for us pest management.However,the host preference research of the larval Scarabaeoidea is still insufficient.In this study,the ultrastructure of the larval olfactory organs of the five species of scarab beetle were observed and compared using scanning electron microscopy;The olfactory organs were functionally examined through organ-ablated test.The host preference were compared through host locating experiments using six-armed olfactometer.1.Anomala corpulenta has seven sensilla basiconica and one sensillum palmatum at the apex of each antennae,and more than 16 sensilla basiconica at the apex of the maxillary palp;A.mongolica bears eight sensilla basiconica and one sensillum palmatum at the antennal apex,and 21 sensilla basiconica at the maxillary palp;A.smaragdina possesses eight sensilla basiconica and one sensillum palmatum at the antennae,and more than 21 sensilla basiconica at the apex of the maxillary palp;H.parallela has 33 sensilla basiconica at the apex of the antenna,and more than 21 sensilla basiconica at the apex of the maxillary palp;P.brevitarsis bears seven sensilla basiconica at antennal apex,and more than 13 sensilla basiconica at the maxillary palp.The results show that sensilla basiconica are commonly present on the antennae and maxillae of the five species.Digitiform organs were discovered at the anterior margin of the maxillary palps.Palmate sensilla were found at the end of the maxillary palp in three species of Rutelinae.The larvae of the five species of scarab beetles share the type of sensilla,but various greatly in number of sensilla.2.Larval host orientation behaviors were compared using six-armed olfactometer,between the normal,antennal ablated,maxillary palp ablated,and the antenna-maxillary palp ablated the larvae of A.mongolica.The result shows that 80.00 ± 10.00% the larvae of control group can detect the orientation of the host plant;Only 6.67 ± 5.77% larvae can detect the host when their antennae were ablated;Only 20.00 ± 10.00% larvae can smell the host plant when their maxillary palps ablated;About 23.33 ± 5.77% individuals without antennae and maxillary palps move toward the host plant.The results reveal that both antennae and maxillary palp play important roles in the larval host orientation behavior.The antennae are very likely more important than maxillary palp.3.The larval host preferences between the five serious white grubs(Anomala corpulenta,A.smaragdina,A.mongolica,Holotrichia parallela and Protaetia brevitarsis)focused on four main crops(corn,soybean;peanut and potato)use six-armed olfactometer.The host preference results show that A.corpulenta prefer to move to soybeans;A.mongolica and H.parallela larvae prefer corn;A.smaragdina prefers peanuts;P.brevitarsis did not exhibit a clear preference on the four crops in the experiment.In this study,the author compares the ultramorphology on the larval olfactory organs of five species of scarab beetles using scanning electron microscopy.The author compares and the functional differences between the antennae and maxillary palps during larval host orientation.The author also investigates the host preferences of the five most serious white grubs focused on the four main crops.This study provides a fundamental for the further study on larval food foraging behavior,and provide new ideas and evidences for the integrative pest management(IPM)of white grubs in future.