Study On Inter-Specific Competition Between Sitobion Avenae(Fabricius) And Rhopalosiphum Padi(Linnaeus)

Sitobion avenae (Fabricius) and Rhopalosiphum padi (Linnaeus) are two important cereal pests in the world and distribute all around China. In most districts of Shaanxi province, S.avenae occur frequently and cause serious damages to the wheat in most time. In recent years the population of R.padi was increasing in some areas of Shaanxi province and caused more and more damages.Generally speaking, there is no inter-specific competition between the two cereal aphids, because their feeding niche has some difference. However, the researches in recent years showed that R.padi significantly upward to wheatear in heading date to expand their niche. Meanwhile, the two aphids'niches overlapping obviously for their feeding and reproduction multiply; there may be a strong inter-specific competition. From the research on two aphids'inter-specific relationship on different wheat variety on different densities we can prove the existence of competition between two aphids and competition constraints, and providing the theoretical basis of pest ecological regulation and aphids'genetic evolution. The main results as follows:1. Because aphids'fecundity similar as a single peak curve under artificial control, and the area under curve means aphid reproductive niche, it can be described by Weibull function. The results showed: the reproductive niche of S.avenae stronger than R.padi's on different wheat variety, that is the area parameter 3.05811 > 2.7044(1376),6.5199>2.5457(xiaoyan-22). And the pre-daily reproduction period niche of R.padi is shorter, so R.padi gets in reproduction peak earlier. That means R.padi has the stronger reproduction and development compete ability.2. The impact on competition of wheat varieties: Compared with high sensitive variety: 1376, when two kinds of aphids parasitized on high resistant variety: xiaoyan-22, the peak of reproductive niche and pre-daily reproduction period niche occurred earlier. The average fecundity of S.avenae on xiaoyan-22 is less than on 1376, while R.padi merely affect by resistant wheat. Therefore the wheat variety has effect on the competition. Xiaoyan-22 can be identified as a resistant variety to S.avenae, but it can't be identified as a resistant variety to R.padi.3. As the number of initial inoculation's increasing, R.padi influenced by density effect more than S.avenae, the average female fecundity and average longevity of R. padi decreasing significantly. Whereas, S.avenae were less constrained by the density effect.4. The inter-specific competition two cereal aphids: (1) on the susceptive variety 1376, the competitive ability of R.padi was stronger than S.avenae in the initial period, manifested as the population of R.padi developed faster. But with their population developing, the population of two aphids achieved balance at the 25th day. Due to high number of two aphids develop on the same plant, wheat was damaged seriously, then two aphids'population were decreasing. But the population of R.padi declined faster. To the 40th days, the population of R.padi was less than 10% of two aphids'number in total. (2) On the resistant variety xiaoyan-22, the regulation of two cereal aphids'competition similar as on the susceptive variety, but the competitive balance date delayed 6-7 days, at the 31st day. So it can make conclusions that in initial period the competitive ability of R.padi was stronger than S. avenae, but the competitive ability of S.avenae was stronger in the late period.This study proved the mechanism of two cereal aphids'competition under artificial control. However, the inter-specific competition is affected by many factors under natural conditions. We also have to do extensive research about different temperatures, humidity and other factors affected on the outcome of competition between two aphids and their replace mechanism of competition.