Population Dynamics Of Small Green Leafhopper And Its Egg Mymarids And The Test Of Toxicity Of Pesticides For The Mymarids

The small green leafhopper (SGL) Empoasca vitwas (G?the) was one of the serious pests commonly occurred at the tea plantations in south of China. The natural enemies of SGL, especially its egg parasitoids, mymaridae, were plentiful and have an important potentiality for sustainable controlling the leafhopper. The unreasonable using of chemical pesticides to control the leafhopper, would cause a reverse action to its natural enemies and depress their sustainable controlling role in tea plantations. As the lack of information on the egg parasitoids of SGL, an preliminary investigation on the population dynamics of SGL and its egg parasitic mymarids were conducted at the tea plantation of Fujian Agriculture and Forestry University (FAFU) from July, 2008 to November, 2009. And the toxicity of several common pesticides to mymarids were tested in the laboratory as well. In order to provided a scientific basis for protection and utilization of the mymarid parasitoids to control the leafhopper. The results were as follows:By plant-flapping, picking shoots, dessecting the SGL's eggs from the tea shoots of 4 tea varieties (Tieguanyin, Huangdan, Fuding Dabaicha and Fuyun no.6) under microscope and rearing the parasitized eggs in laboratory, the population dynamics, the egg density and parasitism of SGL, a significant positive correlation among the population dynamics of the eggs, nymphae and adults of SGL in 4 tea varieties was shown. Which indicated that the population dynamics of SGL were generally similar to each other in the 4 tea varieties. The population dynamics of SGL had two population peaks annually and the first peak was higher than the second one. The egg parasitism of SGL were basically consistent within the 4 tea varieties investigated, which was highest in the winter and lowest on April and varied with the egg density of SGL on the tea shoots, except for that in the cold season.Using Bifenthrin,Acetamiprid,Imidacloprid,Azadirachtin,Rotenone,Metolcarb,Dimethoate pesticides liquid by membranous residue, feeding mymarid adults and immersing the parasitized eggs 3 methods to test the sensitivity of mymarid adults, their parasitized eggs and the LC50, the results were as follows:The toxicity of different pesticides to mymarid adults in liquid membranous residue method showed that they were highly sensitive to all the 7 pesticides tested and their mortality reached to 100% within 12h after treated. Their longevity had no significant difference in all the different pesticides and concentrations. The results of feeding mymarid adults method was same as the membranous residue method.The affection of the adult emergence and their longevities in immersing the parasitized eggs method, it showed that different pesticides had different affection to the mymarid adult emergence. The adult emergence rate was lowest after Rotenone treated, while the emergence rate was highest after Imidacloprid treated. The affection of different concentrations to the adult emergence was consistent and increasing in accordance with the pesticide concentration increased. The longevities of mymarid adults varied significantly with the different pesticide and its concentration treated.By using membranous residue to test the LC50 of several common pesticides to mymarid adults, it showed that the toxicity of Bifenthrin was the highest for female mymarid adults within 12h and 24h after treated (11.821μg/L,6.143μg/L) and the toxicity of Acetamiprid was the lowest (1174.16μg/L,599.210μg/L). The toxicity of Bifenthrin was the highest for male mymarid adults within 12h and 24h after treated (0.901μg/L,0.274μg/L) and the toxicity of Acetamiprid was the lowest (965.274μg/L,783.113μg/L). The result indicated that the toxicity of the pesticides tested for mymarid adults from high to lower were ranged as: Bifenthrin> Metolcarb> Rotenone> Imidacloprid> Azadirachtin> Acetamiprid.Since the commendatory concentration of the 7 common pesticides for SGL controlling in the fields had significantly higher toxicity for the parasitic mymarids and in order to protect the mymarid and other natural enemies, it suggested that these 7 pesticides should be strictly forbidden using in organic tea gardens and using as less as possible in the common tea gardens when necessary.