Genetic Variation of Host Populations of Liriomyza sativae Blanchard

In this study, partial sequences of the mitochondrial cytochrome oxidase subunit I （mtDNA-COI） gene and the ribosomal internal transcribed spacer 1 （rDNA-ITS 1） gene, isolated from five artificial populations of Liriomyza sativae （Diptera： Agromyzidae）, were sequenced and compared, to analyze their genetic variation. Analysis of the mtDNA-CO1 gene showed that a low genetic variation was detected among the five populations and only five variable sites were found in the nucleotide sequences. Most of the observed variations that occurred within the populations were because of nucleotide transitions, whereas, the interpopulation variation was because of the differences in haplotype frequencies occurring among the host populations. Analysis of the rDNA-ITS1 gene revealed a small diversity in the five host populations. The trend of genetic differentiation in the host populations was consistent with the preference of L. sativae to the plant hosts.

Genetic Variations Among Liriomyza sativae Blanchard Populations Indicated by β-tubulin Gene Sequences

To analyze the genetic differentiation of the host- and geo-populations of Liriomyza sativae Blanchard, the β-tubulin gene of 5 host-populations and 6 geo-populations of L. sativae was sequenced. Subsequently, the sequences were analyzed by biosoftware DNAStar and MEGA, and the phylogenetic trees constructed. The results obtained by the two softwares were similar, that is, the sequences of β-tubulin gene were more than 98% homologous, among the host- and geo-populations of L. sativae, with only 8 variable sites, but no insertions and deletions were detected. It seems that differentiations in β-tubulin gene among the host- and geo-populations of L. sativae are related to the hobby to hosts and the geographical distributions, respectively.

Comparative demography of Liriomyza sativae Blanchard （Diptera： Agromyzidae） on cucumber at seven constant temperatures

Reproduction and population parameters of vegetable leafminer, Liriomyza sativae Blanchard were measured on cucumber （Cucumis sativus L.） at seven constant temperatures （10, 15, 20, 25, 30, 35 and 40℃）. No eggs were found at 10℃ and flies died after exposure to 40℃. The significantly highest intrinsic rate of natural increase （rm）, net reproductive rate （R0） and finite rate of increase （λ） ofL. sativae were obtained at 25℃ as 0.196, 52.452, and 1.216, respectively. The above-mentioned parameters decreased at 15℃ and 135℃ and this reduction at 35℃ was strong. Doubling time （DT） varied significantly with temperature. The shortest doubling time was obtained at 25℃. Mean generation time （T） decreased significantly with increasing temperature between 15℃ and 35℃. Percentage of immature ages in the stable age distribution was more than 95% at all temperatures. Female longevity was greater than male at all temperatures. Liriomyza sativae lived for a long time at 15℃, whereas at 35℃ had lower survival rates. The effect of temperature on reproduction, especially the intrinsic rate of increase of L. sativae would be useful for predicting its longterm population fluctuation over several generations.

Abamectin resistance in strains of vegetable leafminer, Liriomyza sativae （Diptera： Agromyzidae） is linked to elevated glutathione S-transferase activity

Abamectin resistance was selected in the vegetable leafminer, Liriomyza sativae （Blanchard） （Diptera： Agromyzidae） under laboratory conditions, and cross- resistance patterns and possible resistance mechanisms in the abamectin-resistant strains （AL-R, AF-R） were investigated. Compared with the susceptible strain （SS）, strain AL-R displayed 39-fold resistance to abamectin after 20 selection cycles during 25 generations, and strain AF-R exhibited 59-fold resistance to abamectin after 16 selection cycles during 22 generations. No cross-resistance to cyromazine was found in both abamectin-resistant strains. However, we failed to select for cyromazine resistance in L. sativae under laboratory conditions by conducting 17 selection cycles during 22 generations. However, moderate levels of cross-resistance to abamectin （6-9 fold） were observed in strains which received cyromazine treatments. Biochemical analysis showed that glutathione S-transferase （GST） activity in both abamectin-resistant strains （AL-R, AF-R） was significantly higher than in the susceptible strain （SS）, suggesting metabolically driven resistance to abamectinin L. sativae. Recommendations of mixtures or rotation of cyromazine and abamectin should be considered carefully, as consecutive cyromazine treatments may select for low-level cross-resistance to abamectin.