| The adaptation and mechanism of "crop-pest-enemy" to elevated CO2are the main research for the effects of global warming on agricultural production. Maize is one of the main food crops in our country. Asian corn borer, Ostrina furnacalis, and the corn leaf aphid, Rhopalosiphum maidis, are key pests in maize production. The study for effects of elevated CO2on growth and development of maize, pest, enemy and their interaction could provide important scientific evidence for evolution rule of "maize-pest enemy" system under climate change in theory, understand occurrence trend of maize pests, enemy control and rational utilization under climate change in practice. This research simulates the growth and development of maize, pest, egg parasitoid wasps and their interaction under elevated CO2. The results are as following:Improved24open-top chambers (OTCs) were setted up for our trial, that adapt to the maize planting and local northeast climate in China. The CO2concentration within the OTCs was stably controled and closed to the required CO2level (fluctuating range less than50μL/L). The temperature and relative humidity in the chambers were higher than outside. The temperature and relative humidity had no difference among different chambers with each CO2level. Therefore, the chambers could keep the air warmer and wetter. The improved OTCs could meet the requirements of trials of effects of elevated CO2on "maize-pest enemy" system.Newly hatched larvae of O. furnacalis were inoculated in maize plants, and maize plants were planted in the OTCs with different CO2levels (ambient CO2,550μL/L and750μL/L). Elevated CO2increased the plant height and yield of maize plants, decreased the TNC: N in maize tissue, decreased the number of survival larvae per plant for second generation. Elevated CO2decreased the wintering larval body weight and supercooling point. Therefore, the cold hardiness of wintering larvae is enhanced under elevated CO2. While the survival rate of wintering larvae had not been influenced by elevated CO2. The number of egg per female was decreased by elevated CO2. Elevated CO2change the nutritional qulity of maize, which decrease the survival fitness of O. furnacalis.The following5treatments were designed to raise O. furnacalis:1) C1(ambient CO2in CDC)+M1(maize planted in OTC with ambient CO2),2) C2(550μL/L CO2in CDC)+M2(maize planted in OTC with550μL/L CO2),3) C3(750μL/L CO2in CDC)+M3(maize planted in OTC with750μL/L CO2),4) C1+M2,5) C1+M3. Compared with C1+M1, the larval duration was longer and its food consumption and frass were increased in other treatments, and there was no significant difference among other treatments. Therefore, with or without the direct effect of elevated CO2to O. furnacalis, the above results had not been changed. Compared with C1+M1, larval body weight and MRGR were decreased in other treatments. Second generation of O. furnacalis was rared in Cl+M1, C2+M2and C3+M3treatments, the change for above measured indexes among three treatment was similar with above, and there was no difference between two generations in the same treatment. Elevated CO2decreased the larval survival rate in the second generation. Threrefore, elevated CO2could indirectly influence the growth and development of O. furnacalis by nutritional qulity of maize.Parasitism capacity of per female trichogramma(Trichogramma dendrolimi and T. ostriniae) and T. dendrolimi population were conducted respectively in CDC and OTC with different CO2concentrations (ambient,550μL/L and750μL/L). Parasitism occurrence rate, number of parasitized eggs, number of emergence offspring per trichogramma, emergence rate and female ratio were not influenced by elevated CO2in CDC. But elevated CO2decreased the body length of offspring for two trichogramma species. To simulate the field release trial for T. dendrolimi in the OTC, egg card was inoculated in maize plant, at the same time the T. dendrolimi population was released. The damage of O. furnacalis to maize and its survival rate were not influenced by elevated CO2, which indicate that elevated CO2do not influence the effect of T. dendrolimi on the control of O. furnacalis. And the more small body of two trichogramma species under elevated CO2may reduce its fitness to eggs of O. furnacalis.The corn leaf aphid, Rhopalosiphum maidis reared on barley for two generations were examined under four treatments:1) control temperature (22/18℃=L/D) and ambient CO2(350-400μL/L),2) control temperature and elevated CO2(750μL/L),3) elevated temperature (26/22℃=L/D) and ambient CO2,4) elevated temperature and elevated CO2. Multiple variance analysis was used in this experiment. The developmental duration for each age stage was significantly reduced by elevated temperature. The elevated CO2only reduced the development time of4th instar nymph, and the succsesive generation reduced the duration of nymph. Thus, the temperature was the dominant factor to development duration of R. maidis. The fecundity of R. maidis was significantly increased under the elevated temperature, CO2and later generation. Elevated temperature and CO2increased the number of winged aphids, which may enhance the aphid migration. R. maidis had the highest rm under the elevated temperature and CO2treatment, and the effect was increased in the following generation. These results indicated that the combined effects of both elevated temperature and CO2on aphid biology may exacerbate aphid damage on barley under the climate with elevated temperature and CO2level. |
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