Effects Of Brassica Alboglabra N:P Ratios On The Growth And Ecological Stoichiometry Of Pieris Rapae

Pieris rapae L.is one of the most harmful insect for cruciferae.The adutls of Pieris rapae L.almost oviposit on cruciferae plants.Eggs were laid usually on the back of leaves with the larger numbers at the first and overwintering generations.Studies on Pieris rapae focused on its ecology,habits,population dynamics,and control strategies,with few on the influences of nutrition on its growth.Thus,this study will from the point of view on ecological stoichiometry to study of the growth and development of Pieris rapae L..According to the theory of ecological stoichometry,nutrition balance,especially the balance of three major elements(C,N,P)are very important to the growth and development of organisms.Thus,in the present study,the nutrition solutions with different N and P contents were made,and the cabbage plants were cultivated in these solutions.The growth and development of Pieris rapae larave were measured and observed.The results are as the following1)There is a positive relationship between solutions with different N and P contents and the N and P contents of Bassica alboglabra,and N,P availability of Pieris rapae were higher with the increase of N,P contents in Brassica alboglabra.2)C content did not vary so largely,and not significantly different with N:C,C:P ratios in the tested plant(p>0.05),and P content was negatively correlated with C:P in this plant.This result is correspondence to the theory of growth rate.The N and P contents in N-and P-limited(20%)cultivated Brassica alboglabra were lower than the high N and P cultivated plants;and the larvae feeding N-and P-limited cultivated Brassica plants had lower body size,pupal weight,and shorter development time,than those feeding high content of N and P plants.3)The N:P ratio between Brassica plants and the larvae of Pieris rapae was positively correlated,and the N and P contents of the larvae increased with the instars of the larvae.P content in the larvae of Pieris rapae increased with the RNA content,and RNA content increased with instars of the larvae.4)Compared to feeding the low N and P content(20%)cultivated plants,the high content cultivated plants reduced the the development time of eggs,1-5 instars,and pupae,i.e.,eggs 4d,1-3 instars 3-4d,4-5 instars 1-2d,and pupae 5-7d,respectively.In conclusion,the N and P concentrations in the nutrition solutions directly influenced the content of N and P content in the plants,and these contents in plants directly determined the N and P contents in the larvae of Pieris rapae.The N and P contents in the solutions indirectly impacted the N and P contents in the larvae,no impact on the C content.N-and P-limited solution retarded the the growth of the larvae of Pieris rapae.The best time for control Pieris rapae would conduct at the third instar,and the present study provide a new insight to the control of Pieris rapae.