| Zanthoxylum schinifolium Sieb et Zucc is an important economic industry in Chongqing. But in recent years Panonychus citri (McGregor), occurred at large and caused serious harm, has become the important pest mite threat of pepper production in Chongqing Jiangjin etc green pepper-producing areas. And the great economic losses of pepper production and quality were caused by this mite. In recent several decades, there were many documents discussed on the hazards, population dynamics, growth and development, physiological and biochemical research and prevention of Panonychus citri in citrus, however, the studies on its hazards on the Chinese prickly ash were seldom reported. Therefore, we choose Chinese prickly ash as host plants to study the effect on the entire population of Panonychus citri of host plants at different temperatures, and this study would provide a useful reference to the integrated management. The key findings were listed as follows:1 The dynamic of the natural population of P. citriSystematic investigations were carried out on the dynamics of natural population of P. citri through a whole year of field investigation. The results showed that the population of the pest mite had one obvious peak. The peak appeared from last ten days in March to the middle ten days of April. There was a significant difference about the density at the year, the density of the pest mite reached 4.92 individuals perleaf, at the last ten-day of March. The range of average density is 0.00～4.92 individuals per leaf. The low density appeared from last ten-day of July to the middle ten days of September. The spatial pattern and time-series dynamics of P. citri in prickly ash were analyzed by using seven indices of aggregation and two regression models. The results indicated that the population of indicated uniformity (I, C_A<0, M~*/M<1) at the middle ten days of February, and spatial aggregation (I, C_A>0, M~*/M>1) from the last ten days of February to early May, then dispersal (I, C_A<0, M~*/M<1) from the middle ten days of May to the middle ten days of July, and aggregation (I, C_A>0, M~*/M>1) at the middle ten days in October.2 Effect of temperature on development and reproduction of P. citri2.1 The relationship between development and temperatureWithin the range of 16～31℃, RH 75%±5%,L:D=14:10, the development durations were shortened with the increase of temperatures. The developmental spans of a generation were 35.93, 24.90, 19.45, 15.63, 14.09 and 11.50 days at 16℃, 19℃, 22℃, 25℃, 28℃and 31℃, respectively. The analysis suggested that the relationship between development and temperatures were fit for Logistic equation model. The developmental threshold temperatures of each stage (egg, larva, nymph and generation) were 7.23, 9.09, 9.67, 8.69℃and the corresponding effective thermal summations were 122.12, 39.44, 68.69, and 259.76 days/℃, respectively.2.2 Effect of temperature on survival rate reproduction of P. citriWithin the range of 16～31℃, the survival rate of egg and larva reached highest 97.94%, 97.78 %, at 25℃. The survival rate of nymph reached highest 97.92% at 22℃. The average number of oviposit was 28.68 eggs at 22℃.2.3 The experimental population life tables of P. citriThe experimental population tables of P. citri, with prickly ash as host plant, were constructed at 16℃, 19℃, 22℃, 25℃, 28℃31℃. The results showed that the net reproductive rate (R_o) of P. citri reached the highest values of 16.8516 at 22℃. At 25℃the intrinsic rate of natural increase (r_m) and finite rate of increase (A.) amounted to the highest value of 0.1235, 1.1314 respectively and the time for population to double (t) was shortest, 5.6142 days. The results above revealed that 22～28℃was the optimum temperature scope for the development and reproduction of P. citri.The experimental population tables of P. citri, with the host plant of citrus as control, were constructed at 16℃, 19℃, 22℃, 25℃, 28℃31℃. The results showed life table parameters of P. citri on the host plant of citrus was better than on the host plant of prickly ash. 3 Density-dependent effects of the experimental population of P. citriThe density-dependent effects of the experimental populations of Panonychus citri were conconducted at 25℃±1℃, RH 75 %±5 % and photoperiod of 14 :10 L:D. The results showed that the density of eggs did not affect their survival and development significantly. The survival rate of the mite was95%～100% and the development period lasted 6.6～6.8 d when the density was in the range of 10～60 eggs per leaf. However, the density of first larvae showed a significant effect on the development, survival, and reproduction of the mite. The survival and development rate of the immature stages declined with the increase of the density in the range of 3～36 individuals/leaf, where as the female to male ratio tended to rise. The relationship between fecundity (Y) and the first larval density (X) could be described as the equation: Y= -9.398lnX+37.666, (R=0.978). |
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