| Phenacoccus solenopsis Tinsley, a worldwide distributive malignant invasive pest, is seriously harmful to farm crops, cash crops and horticultural plants. For its wide host range and strong adaptability, P. solenopsis has caused devastating blow to cotton industry. In China, the pest has spread to15provinces and districts including some cotton regions, which brings about enormous realistic harm and potential threat to agricultural production. To further understand the population dynamics and adaptive capacity to different hosts, this paper systematically studied the influences of temperature and relative humidity on the growth, survival, fecundity and longevity of P. solenopsis, and the suitable environmental conditions had been predicted at the same time. The free choice of host and the effects of different hosts on the population fitness of the pest were also studied to make its potential threat to different hosts clear. The main results were as follows:1. The survival rates and developmental periods of each instar, female ratios, longevity and fecundity of females were significantly affected by temperature and humidity. In general, at the same temperature, the survival rate increased with humidity while at the same humidity, there was a parabolic relation between survival and temperature. When the relative humidity (RH) was45%,60%and75%, the survival rate had some difference at different temperatures, and the peak of survival rate was at25℃while the minimum were at15and35℃. At15,20and25℃, the duration of nymphs was longer at45%RH, and was shorter at75%RH, but the results were contrary at30and35℃. That is, at the range of15-35℃, mealybug nymph developed faster at lower temperatures and higher humidity, and at higher temperature and lower humidity. The order of nymph duration from short to long was30°×45%RH<30℃×60%RH<25℃×75%RH. At the same temperatures, the lifespan of female adult extended with the increase of humidity, and it reached the peak at20℃. When temperature was constant, the entire lifespan was positively corrected with humidity, as it got the peak at15℃×75%RH, and got the minimum at35℃×45%RH. Adult cannot complete its life cycle because of its zero fecundity at15and35℃. At the same temperatures, female ratios were relatively high at low RH, in the effective temperature range (20-30℃), it got the highest at20℃×45%RH (67.90%) while got the lowest at20℃×60%RH (35.78%). The fecundity reached the highest at30℃×45%RH, which was up to464.00nymphs per female, and it reached the lowest at20℃×45%RH, only152.08nymphs per female. At each RH, the developmental threshold temperature of2nd instar nymphs was the minimum (the lowest temperature was9.59℃at75%RH), and the required effective accumulated temperature was the maximum (at60%RH the maximum was119.29d·℃). At75%RH, the entire generation developmental threshold was the lowest (10.65℃), and the required effective accumulated temperature was the maximum (308.77d·℃).30℃×45%RH was the most favorable temperature and RH combination for the optimal population growth of this mealybug.2. There were obvious differences and preference for each instars in choosing seven different hosts. The order of feeding preference of each instar was as follows.1st instar: Bidens pilosa=Gossypium spp.>Solanum tuberosum>Malvaviscus arboreus> Ipomoea batatas>Hibiscus rosa-sinensis>Lycopersicon esculentum.2nd instar: Gossypium spp.>M. arboreus=B. pilosa>L. esculentum>S. tuberosum=H. rosa-sinensis>I. batatas.3rd instar:Gossypium spp.=M. arboreus>H. rosa-sinensis=B. pilosa>S. tuberosum=I. batatas>L. esculentum. Adult female:Gossypium spp.=H. rosa-sinensis=M. arboreus>B. pilosa>S. tuberosum>I. batatas=L. esculentum.3. The survival rate, developmental duration, female ratio, longevity and fecundity of females were different on different hosts. Nymphal survival rates were higher on M. arboreus, I. batatas and B. pilosa, the lowest was on L. esculentum. The longest nymphal developmental period was on B. pilosa (16.45d), the shortest was on M. arboreus (11.67d). The entire lifespan of female on B. pilosa was the longest (62.10d), the shortest were on I. batatas and L. esculentum (40.99d and41.03d, separately). Female rations were the highst on L. esculentum and S. tuberosum (69.08%and69.00%, respectively), on M. arboreus was the lowest (53.55%). The fecundity was the highest on M. arboreus, up to647.92nymphs per female, followed by S. tuberosum (503.33nymphs per female), the lowest was on I. batatas, only171.09nymphs per female, followed by B. pilosa (195.33nymphs per female). Experimental population life table parameters indicated that, M. arboreus was the most suitable host for P. solenopsis, S. tuberosum was the second, followed by Gossypium spp. However, B. pilosa, mealybug favorite host was not suitable for its growth and development.4. The order of soluble sugar content of each host was as follows:H. rosa-sinensis>Gossypium spp.>S. tuberosum>M. arboreus>I. batatas>B. pilosa>L. esculentum; The order of soluble protein content was:B. pilosa>S. tuberosum>I. batatas>H. rosa-sinensis>L. esculentum>M. arboreus>Gossypium spp.; The order of tannin content of each host was:Gossypium spp.>I. batatas>H. rosa-sinensis>M. arboreus>B. pilosa> S. tuberosum> L. esculentum.5. In general, it is the volatile substances which can attract insects to feed. And, in this paper, there was no significant correlation between food preference of the mealybug and the content of soluble sugar, soluble protein and tannin of the tested host. |
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