The Effect Of Less Preferred Vegetables Against The Bemisia Tabaci On Cucumber And The A Preliminary Study On Its Mechanism

After the successful invasion since90s20century, the whitefly Bemisia tabaci (Gennadius) of biotype B has broke out and caused serious economic loss in many places in China. Now biotype Q which replaced the biotype B has developed to be one of the most important pests of agriculture and horticulture. B. tabaci has been recorded from more than600plant species of74families. It has different preference for whiteflies to select different host plants, and its’ frefered host plants were cucumber, tomato, cabbage, cotton, tabacco, etc; nevertheless, there are still many less prefered host plants for whiteflies, some of them may possess a repellent effect against the whiteflies. It has rarely reported that the whiteflies controlled by utilizing less prefered host plants. So the research on the less prefered hosts could provide theoretical basis for developing efficient repellent, new ideas and approaches for controlling the whitefly. From2010to2012, in Beijing and Zhuozhou of Hebei, there are five less prefered vegetables including celery (Apium graveolens), asparagus lettuce (Lactuca psativap L. var. asparaginap Bailey), malabar spinach (Gynura cusimbua (D.Don) S. Moore), edible amaranth (Amaranhus mangostanus L.), water spinach (Ipomoea aquatica Forsk.), were selected to do the research in laboratory and field respectively. For probing the bio-chemical relationship between the whiteflies and their host vegetables, their preferred and less prefered vegetables and some of their volatiles were tested by Y-tube olfactometer bioassay and HS-SPME-GC\MS. The field intercropping experiment has verified the roles of the5kinds of host vegetables on lowing the density of whitefly on cucumber. At last, the recombinant CSP gene of B biotype was obtained by methods of molecular biology, and the expression of different instars and parts of whiteflies biotype B were investigated. The following is the main results:(1) By the Y-tube olfactometer bioassay, the response rate and selected rate of both biotype whiteflies to the five less prefered vegetable extracts were lower than that from cucumber. And the relative selected rates of both biotypes to the five less prefered extracts were significantly lower than cucumber. There is a repellent effect against the whitefly from the five vegetables. Whereas, there showed a different select behavior to the five vegetables between the two biotypes of the whitefly.(2) In the open field, population densities of whiteflies on the cucumber intercropped with either one of five less prefered vegetables were significantly lower than those of monoculture cucumbers; Similar trend of the whitefly population was also found from those experiments carried-out in the green houses, but only with significant decreases observed from cucumber intercropped with celery and malabar spinach.(3) The result of HS-SPME-GC\MS showed the volatile profiles from celery, malabar spinach and cucumber consisted of four major groups of compounds, fatty acids, terpenes, aromatics and hydrocarbons, as well as their derivatives. In cucumber plants, hydrocarbons were the dominant group of chemicals identified, followed by aromatics and fatty acids. For celery, terpenoids and their derivates were the major constituents with more than90%compounds identified. Terpenoids and hydrocarbons were found also higher in malabar spinach. D-limonene was dominant in celery and Geranyl nitrile was the main volatile in malabar spinach.(4) In the validation test by Y-tube olfactometer between the main volatile components from the less prefered vegetables and their identical chemicals, the two biotype whitefly adults had a lower action and selectance to Limonene, D-Limonene and geranyl nitrile. The results mean that D-Limonene from cellery and geranyl nitrile from malabar spinach are the volatile chemicals to repel the whitefly. It exists difference between the biotype B and Q for their selectance to some volatiles.(5) By the biotech of RNA extraction and RT-PCR cloning cDNA etc, a CSP gene was cloned from B. tabaci biotype B after the sequence analysis. The gene was completely coincidence with that BtabCSP (GU250808) from biotype Q.