Studies On The Interaction Between Aphidius Gifuensis And Beauveria Bassiana: Implications For Biological Control Myzus Persicae

Myzus persicae (Sulzer) is of great significance pest on agriculture and forestry. It spreads all over the tobacco producing area in our country and caused a serious loss. Because of its particular ecological strategy and increasing insecticide-resistance, the ordinary insecticides can not control it well. So the research on multi-biocontrol to M. persicae became a hot issue currently at home and abroad. Thus, this paper exploited the ability of Aphidius gifuensis (Ashmead) to control M. persicae in laboratory and the influence of Beauveria bassiana (Balsamo) to the life parameters, parasitical behavior and control efficiency of A. gifuensis in order to provide reference of cooperating entomopathogenic fungi and natural enemy to control pest, and find a effective strategy of Integrated Pest Management of M. persicae. The main contents and conclusions are given below:1 Functional response of Aphidius gifuensis to Myzus persicaeEach female wasp was given 5,10,20,40 and 80 nymphs in 2nd to 3rd instar everyday until death when held at 25±0.5℃, 75%±5% (RH) and 14 L:10 D. Recorded the amount of parasitized aphis and the days of survival of parasitoid. The result reflected that the amount of adult wasps parasitizing changed due to different supply of aphis per day. The amount was 24 and 36 when the supply of aphis was 5 and 10 accordingly. It rosed to 60 to 80 when given more than 20 aphides per day and showed nearly no significant difference when given 40 and 80 aphis per day. The wasps began to die from the 5* day and almost died out till the 9* day. The longevity of the A. gifuensis was 5.6 to 6.4 d. The survival of adult wasps had no relationship with density of the host contrary to fecundity. The parasitical function followed the HollingII, where, a=1.1953, T_h=0.0618, N_a=1.1953N_o/ (1+0.0738N_o), and the biggest amount of wasps parasitizing was 16.2 per day.2 Impacts of Beauveria Bassiana on life parameters and control efficiency of Aphidius GifuensisImpacts of Beauveria bassiana on life parameters and control efficiency of Aphidius gifuensis were assessed in laboratory. The groups of aphids were sprayed with B. bassiana at the dose of 1900 conidia /mm² at different stages of parasitism, and both mycosis infection rate or mummification rate of Myzus persicae and emergence rate of A. gifuensis from mummified aphids were recorded. The results suggested that mycosis in treated aphids or mummies, as well as adult emergence of A. gifuensis was significantly affected, varying with inoculation time of the fungal spores. As compared with control, fungal inoculation at 1 day before, the same day and 3 days after A. gifuensis parasitization, caused about 59.6%, 56.2% and 34.8% aphids being infected, and reduced mummification rate by 94 %, 59 % and 47 % and emergence rate of mummified aphids by 83%, 54 % and 49 %, respectively. However, spraying B. bassiana at 5 days after A. gifuensis parasitization, little impaction on mummification and emergence of A. gifuensis from mummified aphids were observed, yet mycosis infection rate was reduced to less than 8.2%. The fungal infection was almost undetected in mummified aphids at 5 or 7 days after A. gifuensis parasitization. When A. gifuensis adults ware sprayed with the fungal conidia, their life-span was shortened about 4 days as compared with control, and approximately 81.8% parasitized cadavers were infected by B. bassiana. The parasitic rate of A. gifuensis adults sprayed with the fungal conidia was not significantly affected, but the survival duration of them in parasitized aphids was shortened by 27. 8% as compared with control.3 The effect of Beauveria bassiana on parasitism behavior of Aphidius gifuensisBioassay was conducted to investigate the toxicity of B. bassiana on M. persicae and A. gifuensis, the results suggested that B. bassiana was virulent to M. persicae and A. gifuensis, the LT₅₀ was 95.13 h and 123.07 h at the dose of 1.0×10⁸ conidia/ml. A. gifuensis parasitized inoculated aphids and uninoculated aphids, because of infecting M. persicae, B. bassiana can impact parasitism behavior of A. gifuensis indirectly, leading to compel A. gifuensis to parasitize uninoculate aphids likely, the parasitic rate was 52.54%, however, 40.19 % inoculate aphids were parasitized. The parasitic rate and parasitic time of A gifuensis adults sprayed with different fungus exposure stages were significantly affected, and the parasitic rate and parasitic time were shorted by 30.9～53.1% and 17.2³3.3% as compared with control.