Effects Of CO₂and Temperature Elevation On Biology And Food Utilization Of Cnaphalocrocis Medinalis（Homoptera:Dalphacidae）

Elevated CO2concentration and temperature are two of the main features of climate changes. Laboratory experiments were conducted to examine influence of elevated CO2on growth, development and food use efficiency of Cnaphalocrocis medinalis in growth chamber. Densities of immature stages of the pest and parasitism by enemy were investigated in the where CO2and temperature were manipulated in a system (free air CO2enrichment, FACE). The fluctuating asymmetry (FA) was also analyzed to morphological traits of adults collected from the field experiment. The main results and conclusions are summarized as followed.1. Influence of elevated CO2on development, fecundity and food utilization. To assess potential influence of elevated CO2on biology of C. medinalis, laboratory experiments were performed to observe development, fecundity, and food utilization under ambient ((370u1/L) and elevated CO2(780μ1/L). Compared with the ambient CO2, under the elevated CO2food consumption and relative growth rate (RGR) of the4th instar larvae increased, but body weight, food consumption, and RGR decreased; in the4th and5th instar larvae frass weight, efficiency of conversion of ingested food (ECI), and efficiency of conversion of digested food (ECD) decreased, but approximate digestibility (AD) increased. Under elevated CO2, pupal duration and weight reduced; survival from egg to adult emergence declined; female proportion increased, but male and female longevity did not change; eggs of next generation decreased in accumulative hatching rate to61day by21.4%, as compared with the ambient CO2. The study suggested that though CO2enrichment increased food consumption of the rice leaf roller, it reduced food utilization rates, and exerted negative impacts on development.2. Impacts of elevated CO2and temperature on density and parasitism. To investigate influence of climate change on abundances of C. medinalis, samples were collected from the FACE experimental plots. Compared with the control, density of the1st instar larvae was significantly decreased under the other treatments (only CO2elevated, only temperature raised, and both elevated); Density of larvae from the1st through to4th instars reduced under treatment of only temperature elevated. Under elevation of both CO2and temperature at the same time was pupa density increased, and number of rolling leaves increased only under raised temperature. There was not significant difference in pupal weight and parasitism rate between treatments. Progeny parasitoid reduced in pupa size by12.5%in length and11.4%in width, and in adult body size as hind tibia length by14.57%for female and17.30%for male, under the elevated CO2as compared with the ambient CO2. The results suggested that elevation of both CO2and temperature might inflict more damage to rice crop by C. medinalis.3. Effects of elevated CO2and temperature on fluctuation asymmetry of adult morphological traits. In order to explore whether stress of climate change lead to morphological fluctuating asymmetry (FA) of C. medinalis, sampling adults from the FACE system was made and analyzed on morphological traits, including forewing (WL1), hind wing (WL2), fore tibia length (FL1), middle tibia length (FL2), and hind tibia length (FL3). The analyses showed that except for FL3under elevated CCb, FL2under raised temperature, and FL2and WL2under both elevated CO2and temperature, the other traits examined exhibited FA. As compared with the control, the FA of WL1reduced under all three treatments, but the FA of WL2and FL1increased under raised temperature only. When poolmg sex variable, five traits showed FA. When compared with the control, FA of WL1reduced under the other treatments; FA of WL2、FL1and FL2decreased under raised temperature only. There were no significant correlations between|R-L|and (R+L)/2in five traits. The results show that morphological FA of C. medinalis adults may be increased by elevated CO2and temperature.