Effect of temperature on the population increase of Liriomyza sativae and Liriomyza huidobrensis(Diptera:Agromyzidae)

Liriomyza sativae Blanchard and Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae) are two small leafmining insects of a wide variety of vegetable and ornamental plants most commonly distributing in temperate areas. The pest status of these two leafminers have dramatically rose worldwide since 1970s with the intensive application of non selective insecticides which led to the elimination of natural enemies, and it is difficult to control them for their polyphagous nature, high fecundity and their capability of quickly developing resistance to insecticide. L.sativae and L.huidobrensis were first reported in China during 1993～1994. Since then, mixed infesting and quick spreading of these two leafminers have been reported in many places in China, but limited biological and ecological studies have been seen in literature. Temperature is one of the most important factors affecting the population dynamics of insects. Therefore, we investigated the development, survival and reproduction of these two pests on cowpea seedlings under seven constant temperatures (17.5～35℃, with a relative humidity range of 65%～85% and a photoperiod of 14L:10D). Mathematical models and life table parameters were used to quantify the effects of temperature on the populations of them. The results were shown as follows: As the temperature rose from 17.5℃ to 30℃, developmental time of L.sativae for eggs, larvae, pupae and the whole immature stages declined gradually from 5.4, 15.7, 19.7, 5.4d to 1.8, 5.4, 7.1, and 12.5d respectively. For L.huidobrensis , the developmental time of corresponding stages reduced from 4.1, 15.9, 14.4, 30.0d to 1.9, 9.3, 8.0 and 17.5d respectively as the temperature rose from 17.5℃ to 27 5℃. The lower developmental threshouds for egg, larva, pupa and total immature stages of L.sativae were at 11.0, 11.3, 10.6 and 10.9℃ respectively, which were much higher than the values of 9.3, 5.3, 7.9 and 7.0℃ estimated for the corresponding stages of L.huidobrensis. The day degree requirements estimated for egg, larva, pupa and total immature stages of L.sativae and L.huidobrensis were 36.4, 100.1, 136.0, 239.3d and 333.1, 193.7, 142.0, 319.0d, respectively. Two nonlinear developmental models, Logistic model and Wang Lan Ding model, gave good fits to the data. At 17.5～30℃, the total immature stages of L.sativae had the highest survivorship at 22.5℃(88.62%), and the lowest at 17.5℃(62.75%); At 35℃, all larvae died before pupa could be formed. High survivorship was recorded for egg (87.65%～95.37%) and the whole larval stages(94.48%～100%). Pupae seemed to be more vulnerable to unfavorable temperatures compared with other stages. Survival rates of pupa was highest at 25℃(95.00%), then clasped from 82.86% to 0% as the temperature changed from 27.5℃ to 30℃. Within the range of 17.5～27.5℃, L.huidobrensis had much lower survival rates in egg, pupa and the whole immature stages in comparison with L.sativae ; High temperature(27.5℃) apparently had a detrimental effect on its various developmental stages, especially on pupa, whose survivorship dramatically dropped from 59.32% to 15.97% as temperature rose from 25℃ to 27.5℃. The whole immature stages of it had the highest survivorship at 20℃(64.03%), and the lowest at 27.5℃(8.11%). Both female and male adults of L.sativae had the longest mean longevity at 22.5℃(♀28.1d,♂16.4d). For L.huidobrensis , the longest mean longevity of female and male were at 20℃(35.1d) and 22.5℃(16.6d),respectively. Female adults lived longer than male adults at all the temperatures tested for both species. Relationship between temperature ( X ) and the mean longevity of female adults( Y ) of L.sativae and L.huidobrensis could be described respectively by quadratic equations ( Y =-0.3280 X 2+15.8159 X -163.5390, r 2=0.9453) and linear equation( Y =-2.3356 X +83.234, r 2=0.9848). From 22.5℃ to 30℃, preoviposition periods of L.sativae reduced from 2.7d to 1.7d, 1.1～1.6d shorter than th