| Ragweed (Ambrosia artemisiifolia), which is recognized as a kind of malignant invasion weed,and it has been spreading in the world. It could make enormous threat on the ecological safety,development of agriculture and human health in the invaded areas. Ophraella communa Lesage（Coleoptera: Chrysomelidae）is an oligophagous leaf beetle that feed to some extent on some membersof Ambrosiinae, feeding and spreading together by adults and larvas. Because of strong host specificityand spread, it become an important natural enemy to control ragweed and under the spot light in recentyears. Now, O. communa Lesage has been applied to control ragweed in central China and south China.According to the climate condition of the area existed O. communa Lesage, all of the main productionregions of sunflowers in our country, such as, northeast, northwest, north China, and so on, may beappropriate for this beelts to live. In no-choice feeding tests under laborstory conditions, this leaf beetlealmost only ate ragweed specially, and also fed to X.sibiricum and A. trifida some extent. In Japan, thisbeetle were founded to feed on sunflowers occasionally in the field, however, it was not founded to eatsunflowers in habitat; multiple selective tests and field tests also proved that O. communa Lesage showextremely low risk to sunflowers. However, some research experts and scholars still doubted thesecurity of this beetle to sunflower. For these reasons, further estimate this beetles’ safty to sunflower,study its population dynamics in north China and make sure effects of their densities to their growingdeveloment and reproduction, these will be important to guide the application of O.communa Lesage.This study analyzed the growing development and reprodunctiong, feeding and oviposition choice of O.communa Lesage on the four test plant species, and researched its host selectivity of sunflowers andragweed and population dynamics under natural condition in northern China, and the last we studied thegrowing development and reproduction characteristics of adults and larvas under the conditions ofdifferent densities. We hope that it can provide the theoretical and practical references to biologicalcontrol common ragweed application of Ophraella communa Lesage. The main results are as follows:1. The growing development and reproduction of O. communa Lesage on different tested plantsIn no-choice feeding tests under laboratory conditions, one day old larvae were released to fourkinds of test plants(A.artemisiifolia, A. trifida, X.sibiricum and Helianthus anunus), recording thesurvival, feather, pupal weight and developmental period of larvae on four kinds of test plants.Compared to survival rate, pupation, feather rate and developmental period of larvae on four kinds oftest plants, and founded that the pupation, feather rate and survival rate of larvae that fed onA.artemisiifolia and X.sibiricum significant higher than the larvae fed on H.anunus and A. trifida, only7.2%larvas which fed on A. trifida developed into adults and only1.1%larvas which fed on sunflowersdeveloped into adults. The developmental period of larvae that fed on sunflowers significantly longer2~3d. The developmental period of larvae that fed on X.sibiricum slightly shorter than larvae fed onA.artemisiifolia. The results show that, A.artemisiifolia and X.sibiricum are fit to O.communa feeding. O.communa that ate A. trifida did not grow well. Sunflowers are not fit this beetle to grow.2. Feeding and oviposition choice of adults to four kinds of tested plants in cages in the fieldPlanted four kinds of test plants (A.artemisiifolia, A. trifida, X.sibiricum and H. anunus) in cages inthe field, and released feathered two days adults on the sunflower, Observed the feeding behavior andoviposition choice of adults on four kinds of test plants. The results revealed that the adults whichreleased on sunflowers transfered fast other kinds of test plants, mainly (68.8%)transfered to ragweed,and a few (21.2%)transferred to X.sibiricum, several (2.5%)transfered to A. trifida to feed and lay eggsand it did not find this beetle on the sunflower after3d. the number of eggs, larvas, pupae and adults onfour kinds of test plants have significant diversity, and the risk index of adults to four kinds of testplants have significant diversity. This leaf beetle did not lay eggs on the sunflower, the risk index is0,and the risk index only12.4%on A. trifida. So, the O.communa which were released in the cages underthe field condition like to feed on A.artemisiifolia and X.sibiricum, and do not choose H. anunus to eatand oviposition, this beetle just eat A. trifida a little.3. The host-selectives and population occurrence of O.communa Lesage in the interplanting ofsunflower and ragweed under natural conditionIn the field of sunflower in Langfang city Hebei province, where ragweed are interplanted, the2-day old adults of O.communa Lesage were released from the insect resource of circle ragweed in thecenter. The feeding, oviposition choice and risk index of O.communa Lesage to sunflowers wereinvestigated as well as the control effect on the ragweed. The results are as follows:(1) O.communaLesage can feed on ragweed by crossing the sunflowers in the field of sunflower. The selective ofO.communa to ragweed has not significant difference in different densities of ragweed (1~9m) anddifferent diversity (1~3plant per clump). The effect of ragweed channel on the spread of O.communaLesage is also not significant. The leaf beetle, insect resource centered, can spread outside and feed onthe ragweed by crossing the sunflowers. the number of laid eggs on the sunflower of O. communaLesage are0.25eggs per plant, respectively. So, O. communa Lesage have hardly to feed and lay eggson sunflower.(2) the difference of number of O.communa Lesage in different parts of ragweed issignificant, and O.communa Lesage gathered feeding on the middle and top of ragweed mostly, so theycan cut off the growing point of hosts, and control the growth of ragweed effectively. The control effectof O.communa Lesage to ragweed is good, as the risk index reaches to95.5%.(3) We found3femaleadults during the over-winter investigation. The mean egg laying amount is281.7, and the mean rate ofegg hatchability is93.6%, under condition of indoor breeding. So it is indicated that O.communa Lesagecan overwinter successfully in Lang Fang, Hebei Province.4. Effects of different densities of adults and larvas on the development and reproduction ofO.communa LesageReleased different densities of adults (1pair per plant,2pairs per plant,4pairs per plant and8pairs per plant) on the ragweed and compare the preoviposition, spawning period and fecundity of adults atdifferent densities. Seting up different larvas densities (5larvas per plant,10larvas per plants,15larvasper plants,25larvas per plants and40larvas per plants) and two kinds of release way (gathered feedingand dispersion feeding) and compare the survival and developmental period of larvas at differentdensities. The results are as follows:(1) Under the condition of different density, the spawning periodand fecundity of adults at different densities have significant difference, the larger the adults density is,the shorter the preoviposition is and the spawning period is longer. But the number of eggs laid perfemale and number of eggs laid per female per day both decreases with the density increasing.(2) Thetwo kinds of feeding way have significant impact on the survival rate, pupation rate and developmentalperiod and pupal development period of larvas, but have no significant impact on feather rate and pupalweight. Different larvae density have significant impact on pupal development period, but have nosignificant impact on other index, Different larvae densities and different feeding way almost have nosignificant interaction. So, the larvae of O. communa develop well in aggregation feeding method.Under the condition of the space volume is0.22m3, the height of ragweed is40~45cm, the number ofleaves are11~13,1~2pair per plant of breeding density is suitable for adults, and there are25larvas aregathered released on one ragweed is suitable.In summary, by in the lab non-selective experiment, field selective cage experiment in the field andselective under natural conditions experiment in the field, comprehensive show that O. communaLesage show very low risk oviposition and feeding selective in Hebei province Langfang city, is safe forsunflower, and this Leaf beetle has good control effect on ragweed, so it make a great applicationprospect in north China. This experiment preliminary clear the effection of Ragweed channel anddifferent ragweed distance and different Ragweed density to O. communa Lesage’s spread. And firstdiscover that this leaf beetle can overwinter in the northern of China.There are important guidingsignificance on the further study population regularity of leaf beetle’s spread and factors affecting thespread. The above research, revealed the safety of O.communca Lesage for sunflowers, and the controleffect and high efficiency to ragweed and in the breeding density effect, this study provide the importanttheory and practice basis for efficient bio-control applied. |
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