| The whitefly, Bemisia tabaci (Gennadius) MED is a destructive insect pest in the world. Ithas a strong invasive ability and first reported in Kunming, Yunnan province in2003. Whereafter,B. tabaci rapid spread coupled with seedlings of flowers and other economic crops, widelydisseminated and outbreaks throughout the country. Now it becomes an important insect pest inmany areas of agricultural production in China. Although The use of pesticides for controlling B.tabaci was effective to a certain extent, it caused many negative effects problem. The lack oftheory accumulation in research and technical guidance in practice in reduce the negative sideafter pesticide. In order to reduce these negative side effects. This paper focuses on B. tabacipopulation dynamics and distribution on main host plants in cotton planting area in north China incotton(Gossypium spp), sunflower (Helianthus annuus L.), cantaloupe(Cucumis melo L.),piemarker(Abutilon theophrasti Medic), common ragweed(Ambrosia artemisiifolia L.). Sunflowerand cantaloupe used as trap plants, corn as a barrier plant, and the B. tabaci obligate parasiticwasps Eretmocerus hayati had released in cotton fields. The biological and ecological controlsystems of B. tabaci were established in cotton field. The main research contents and conclusionsare as follows:(1) A systematic field survey was conducted on81plant species to investigate their suitability ashost plants for the B. tabaci in2012at Langfang, Hebei Province. A total of37species of thesurveyed plant, including Zea mays L., Sorghum bicolor (L.) Moench and Setaria italica (L.)Beauv. were not damaged by B. tabaci. Forty-four species of the investigated plants were suitableas host plants for B. tabaci such as Althaea rosea (L.) Cavan, Helianthus annuus L. and Nicotianatabacum L.. B. tabaci densities on these host plants varied widely. The B. tabaci occurred most onMentha arvensis L., Schizonepeta tenuifolia Briq, Glycyrrhiza uralensis Fisch, Mentha canadensisL., Leonurus japonicus Houtt, Crotalaria pallida Ait., Chrysanthemum paludosum Poir,Achyranthes bidentata Blume, Oenothera erythrosepala Borb., Echium vulgare L., Medicagosativa L. and Ocimum basilicum L., on these plants the infection rate was grade4(>50individualsper100cm2leaf). The plant A. rosea (L.) Cavan, H. annuus L. and N. tabacum L. had somewhatlower densities per100cm2leaf, but being much larger than the former ones, whole plantssupported large B. tabaci populations. H. annuus, Z. may and S. bicolor were widely planted incotton production areas in northern China, and the economic losses caused by B. tabaci infectionon these plants were relatively low, H. annuus can be used as a trap crop, while Z. may and S.bicolor can be used as barrier crops to manage whiteflies in cotton fields.(2) The distribution and dynamics of B. tabaci were evaluated on cotton and six other,co-occurring common plants over two-years field investigation in a cotton-growing area in2011and2012in northern China. The seasonal dynamics on the various host plants, standardized by thequartile method showed that B. tabaci appeared on weeds [common ragweed(Ambrosia artemisiifolia) or piemarker(Abutilon theophrasti)] around the cotton field about10days earlierthan in cotton, followed by other cultivated plants. The peak population dates covered a span oftwo to three weeks on cotton, starting in early August and ending in mid-August in2010, andfrom mid-August to early September in2011. Common ragweed growing adjacent to cottonsupported the highest B. tabaci, densities,22fold and12fold than in cotton in2010and2011,respectively. Sunflower had supported more B. tabaci than the other plants, about1.5-2x higherthan cotton. The above survey results indicate the possibility that weeds around cotton fields canincrease the population density on cotton, while sunflower can act as a trap crop, decreasing pestpressure by B. tabaci on cotton.(3) Use the cantaloupe and sunflower as trap crops, maize as a barrier crop planted intercroppingwithin or as a perimeter crop planted all around the cotton fields. Through a systematic fieldsurvey of the B. tabaci population densities were conducted on different planting cotton,cantaloupe and sunflower at Langfang, Hebei Province. The results showed that all plantingtreatments were significantly lower B. tabaci densities compare to the control cotton especially inB. tabaci main activity period. The lowest B. tabaci densities B. tabacioccurred on cotton in thepattern of B. tabacimaize as a intercropping or as a perimeter crop planting around cottonrespectively. The control effects of B. tabaci on cotton in intercropping pattern was better thanthat on perimeter pattern. The cantaloupe has a strong ability to attract B. tabaci and it wassupported large B. tabaci populations than on cotton and sunflower both in immatures and adultsduring whole sampling seasons. Choose the suitable season to plant cantaloupe is very importantdue to relatively shorter growing period in cantaloupe than in cotton. Planting cantaloupe around40days later to cotton can be seen as the best season in this trapping system and this can becoincided with the vigorous growth time between these two crops so that to achieve the goodcontrol effect.(4)Tomato as a banker plant was used to release the Eretmocerus hayati in trap-barrier croppingsystem in cotton field before B. tabaci outbreak time in2012at Langfang, Hebei Province.Through systematic field survey was conducted on B. tabaci and the number of parasitized by Er.hayati. The resulted showed that perimeter pattern can‘t successfully reduce the B. tabaci densityon cotton compare to control which one was monoculture by cotton. When enter into the mainactivity period the densities of B. tabaci were significantly reduced in intercropping cottonscompare to perimeter cottons. The treatment of maize intercropping within cotton has supportedlowest B. tabaci density in cotton among all of them. B. tabaci population densities on cantaloupeand sunflower were higher than on cotton, and cantaloupe has supported highest B. tabacipopulation in all of the crops during its growing season. In addition, the results showed that theupper and middle positions of plant was supported higher population densities than on lowerposition, vertical distribution pattern of B. tabaci density on cotton plant was belong to clumpeddistribution. The horizontal distributions of B. tabaci immatures were related to uniformdistribution and there were no differences of the population densities between the edge and the center in cotton fields. The adults B. tabaci densities in the center of cotton field were higher thanin the edge of cotton field at all of the perimeter treatments in main activity season, while thepopulation density in different intercropping patterns were no significantly different between i nthe edge and center of the cotton fields. The distribution pattern of the adults population wasbelonging to clumped distribution and the population was mainly distributed in the center ofcotton field. The parasitized densities of Er. hayati have no significant difference among differentperimeter cottons, while the densities in different intercropping cottons were achieved higherparasitized than in control cotton. The rate of parasitized nymphs change was different from theparasitized densities in different planting cottons; it was decided by both the number of B. tabacinymphs and the parasitized densities. The rate of parasitized nymphs on cotton which in thepattern of perimeter cantaloupe and perimeter maize achieved the higher parasitized nymphs thanin control cotton, while the cotton in the pattern of intercropping sunflower can supported thehighest parasitized nymphs in intercropping pattern. For the main predator natural enemiespopulation, there were no differences of the number of predator among different planting cottons.The number of predators was significantly different among cantaloupe, sunflower and maize;sunflower can supported the highest Orius minutus population than on cantaloupe and maize, andthe Orius minutus population in intercropping sunflower was higher than in perimeter sunflower.Sunflower in perimeter pattern supported the highest Chrysopa septempunctata population than inother crops in two different planting patterns. Maize supported the highest population of thePropylaea japonica and Misumenopos tricuspidata than on cantaloupe and sunflower, thepopulation in intercropping maize was higher than in perimeter maize. The B. tabaci populationdensity in2012was lower than in2011during most sampling seasons on cotton showed thatreleased the Er. hayati in trap-barrier cropping system was greatly increasing the control effect toB. tabaci in cotton field.(5) To explore the sustainably effective biological control measure to suppress super pest B. tabaci(Gennadius) MED and better understand the biological control effects of single and multiplereleases of parasitoids, we evaluated the performance and interaction of two aphelinid parasitoidsof B. tabaci, Eretmocerus hayati Zolnerowich&Rose (an exotic primary parasitoid) and Encarsiasophia Girault&Dodd (an autoparasitoid, which is controversial in biological control program).Single species and two species were jointly (1:1,1:3and3:1density ratio) released in field cageson cotton in Hebei Province, China,2012. Results of the field cage experiment showed that allparasitoid release treatments were successful in reducing the densities of the host B. tabaci relativeto the control where no parasitoid was released. The combined release ratio of two parasitoidspecies in Er. hayati to En. sophia at3:1showed the highest control effect throughout treatments.Different population growth trajectories indicated asymmetric competitive effects of En. sophia onEr. hayati. Our results demonstrated interspecific competition between autoparasitoid En. sophiaand exotic primary parasitoid Er. hayati. However, no evidence indicated that autoparasitoid En.sophia disrupted the host suppression achieved by primary parasitoid Er. hayati. The release of density ratio in primary parasitoid were greater than or equal to autoparasitoid together caneffectively control B. tabaci. |
PDF Full Text Request