Studies On The Population Dynamics Of Periphyllus Koelreuteriae And Its Ecological Characteristic

Periphyllus koelreuteriae(Homoptera: Aphididae) is a pest of Sapindaceae: Koelreuteria. In this paper, field survey and laboratory test were carried out to study the ecological characteristic of P. koelreuteriae. The population dynamics, temperature effect and functional response of P. koelreuteriae were focused on in this paper. The results of study as follows:1 Population dynamics of the P. koelreuteriaeThrough field survey in 2013~2014, the P. koelreuteriae overwintering eggs began to hatch in early March. The P. koelreuteriae peak appeared in April to May, and it began to disappear in the first ten days of June. The diapause aphid of P. koelreuteriae happened initial period in mid April, the peak period in mid May and it was recovery activity in early September. From the late October to late November was the sexual aphid peak and spawning peak concentration in the mid to late November. The P. koelreuteriae overwintered in fertilized ovum.2 The effects of temperatureThe results showed that no nymph hatched at 29 ℃, and the developmental duration of egg and nymph decreased with the temperature increasing from 12 ℃ to 23 ℃. The longest duration of egg and nymph was 13.97 d and 21.94 d at 12 ℃, and the shortest was 5.86 d and 7.34 d at 23 ℃, respectively. The relationship between the developmental rate and temperature could be simulated by the Logistic model. Adult lifespan and pre-reproduction period decreased as the temperature increased, and the highest fecundity per female was 107.06 and 120.23 at 18 ℃ and 23 ℃, respectively, while the lowest was 63.16 at 26 ℃. The developmental threshold temperature of egg, total nymph stage, and the whole generation are estimated to be 3.07, 5.40, 3.89 ℃respectively, and their accumulated effective temperatures are 125.02, 140.08, 274.51 degree-days respectively. Analysis of life table parameters showed that the net reproductive rate(R0) and the intrinsic rate of increase(rm) increased as the temperature increased, with the highest values of both found at 23 ℃. Temperature has great effects on the development and reproduction of P. koelreuteriae, and the most suitable temperature range for this pest is from 18 ℃ to 23 ℃, during which there is higher intrinsic rate of increase.3 Functional responses of Harmonia axyridis to P.koelreuteriaeThe results indicated that functional responses of H. axyridis, including adults and 3s t larvae against P. koelreuteriae belonged to Holling-Ⅱ model. The maximum predation quantity of H. axyridis adult and the third instar larvae to P. koelreuteriae were 76.89 and 32.97 in 24 h. And the instantaneous attack rates were 0.0975 and 0.0925 per day respectively, the disposal time were 0.3121 h、 0.72779 h respectively. The feeding amount of H. axyridis increased with the increase of quarry density, whereas the searching efficiency decreased with the increase of predator density. The distribution of aphid affected the selection of H. axyridis adults. With the increase of the number of the leaves, the environmental resistance increased when the natural enemy was hunting for the preys, and the predation efficiency was low when the spatial heterogeneity was complex.