| The diamondback moth (DBM), Plutella xylostella L. (Lepidoptera:Plutellidae), is one of the most destructive pest that attacks Brassica vegetable crops around the world. Previous research on landscape ecology had indicated that landscape diversity and altitude had a great effect on the insect’s survival and reproduction, which gave us a new approach to control the DBM. The researches investigated the fitness of DBM in different landscapes and at different altitude and explained its molecular mechanism by RNA-seq. The major results are as follows:1. The eggs laid per female decreased notably along with the increase in landscape diversity (The percentage of non-crop habitat, Zhang Pu:30%～59%; Jian Ou:29%～60%) that resulted in a decline in population density. However, the oviposition per female decreased in complex landscape. Meanwhile, the population density increased significantly along the landscape scales increasing (The length of square is 50 m,100 m and 200 m, respectively).2. The size of samples collected at the altitude of 226 m is the smallest, including the lightest pupa and adult weights, the smallest size of adult body and wing area. Also, the feeding area, mating success rate and fecundity at the highest level. Because of these, the intrinsic increase rate (r), the finite increase rate (λ) and the net reproduction rate (Ro) reach to the highest level. It is concluded that the most suitable altitude for DBM’s reproduction is at this elevation out of the 5 investigated altitude. At high elevation area(AL:860 m to 1020 m), the size of DBM became bigger which is good for its survival and mating. The big size probably attribute to the FPKM of genes (Px008118) promote growth significantly increased and the inhibited genes (Px010230) decreased. On the other hand, the FPKM of Hamelin and PO which is related to immunity system and CAT and POD related to self-protection system increased significantly. Therefore, we conclude that altitude changed the morphology and physiology of DBM by affecting the FPKM of related genes which ultimately enhanced the DBM’s survivability and improved the larva’s survival rate.3. The eggs laid per female and decrease in the longevity of adult means the decrease in fecundity. According to life history trade-off theory, we suppose improving the survivability take away more energy so as to less energy left to reproduction. Therefore, we checked the FPKM of genes related to metabolism and found that the genes used to carry insulin increased and IDE decreased which resulted in increase of insulin. Besides, the FPKM of PGI and SDH which are the key genes in glycolytic pathway and tricarboxylic acid cycle increased notably which indicated the increase in energy consumption. We concluded that maintaining life in high altitude areas consumed more energy.4. We also found the genes about juvenile hormone (JH) changed greatly. The FPKM of juvenile hormone esterase (JHE) and juvenile hormone binding protein (JHBP) increased while juvenile hormone epoxide hydrolase (JHEH) decreased which indicated that the juvenile hormone would be up in high altitude. Although the fecundity was decreased, the higher level of sex ratio and hatching rate offset it to some extent.Thus it can be seen that there is a trade-off between survival, fecundity and survival of larva in different landscapes and altitude. Generally, the DBM chooses to invest more energy to survival and larva’s survival but less energy to reproduction within certain source so as to keep the biggest fitness. These adaptation features ensure the population survival in unfavorable circumstance. |
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