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The physiological adaptations of biological control agents may determine where and when they will be successful. Agasicles hygrophila Selman & Vogt, has been introduced into China for biological control of an invasive weed, Alternanthera philoxeroides (Mart.) Griseb. The extent to which A. hygrophila can withstand low temperatures was tested to determine whether this physiological trait can be used to predict its potential distribution and effectiveness as a biological control agent. Our results showed that A. hygrophila eggs, larvae, pupae and adults had similar super cooling point temperatures (SCPs) which were not affected by acclimatization. Mortality increased with decreasing temperatures and with length of exposure to low temperatures. SCP was the limiting survival temperature, and chilling injury was one of the main causes of death. The upper limit of chill injury zone (ULCIZ) was 6.7 °C and the sum of injurious temperature (SIT) was about 15.0 degree days. Based on adult cold tolerance, the distribution of A. hygrophila in China is unlikely to extend beyond areas that experience temperatures at or below −8 °C, and the flea beetles will probably overwinter successfully only in areas where the annual minimum air temperature remains above 6.7 °C. These predictions were compared with known distribution data and seem to be a reliable and economical method to predict effectiveness of potential of biological control agents in regions with extreme climates. [ABSTRACT FROM AUTHOR]

Non-target plant selection tests using 20 representative species showed that Agasicles hygrophila could feed on Alternanthera sessilis, but the mature larvae did not pupate successfully. A. hygrophila could not complete their life cycle on the other plant species tested. Thus, A. hygrophila is safe for controlling Alternanthera philoxeroides in China. [ABSTRACT FROM AUTHOR]

Abstract: Agasicles hygrophila has been used as a biological control agent on invasive alligatorweed, Alternanthera philoxeroides in China. We conducted tests to determine the impact of A. hygrophila on the non-target species A. sessilis and examined the developmental differences of A. hygrophila raised on these two plant species to assess the ecological and environmental safety of the introduced A. hygrophila in China. No significant differences were detected in the developmental timing of A. hygrophila from larvae to adults, in larval hatching, and in pupal fresh weight in three treatments: A. hygrophila reared on A. philoxeroides through all life stages; A. hygrophila larvae reared on A. sessilis but pupated in the stems of A. philoxeroides; and A. hygrophila reared on A. sessilis through all life stages. However, when A. hygrophila larvae were reared on A. sessilis but pupated in the stems of A. philoxeroides, they had a significantly longer preoviposition period, lower pupation rate, and lower fecundity than those in other two treatments. The demographic parameters examined indicated that lower fecundity (GRR, R 0) and intrinsic rate of natural increase (r m =0.06), but longer doubling time (T d) were found in A. hygrophila larvae reared on A. sessilis but pupated in the stems of A. philoxeroides compared to the other two treatments (r m =0.11). Ultimately, A. hygrophila has limited effects on the non-target A. sessilis and is considered safe to the ecosystem. Moreover, A. sessilis would provide a marginally suitable host for A. hygrophila in regions where the two species intermingle. [Copyright &y& Elsevier]