Intraspecific cold tolerance of the weed biological control agent alligatorweed thrips, Amynothrips andersoni, in the USA

Abstract

ABSTRACT Biological control of the invasive plant, alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.) is geographically variable, due in part to reduced overwintering survival of control agents in cold climates. Alligatorweed thrips, Amynothrips andersoni O’Neill, may have more utility in colder climates than the widely-established alligatorweed flea beetle, Agasicles hygrophila Selman & Vogt, due to greater cold tolerance. However, it remains unknown whether variation in cold tolerance exists among introduced A. andersoni populations or whether it is driven by local adaptation, leading to enhanced cold tolerance in high-latitude populations. We cultured six populations of A. andersoni from field sites spanning seven degrees of latitude in Louisiana, Arkansas, and North Carolina, USA then compared cold tolerance as supercooling point, chill coma temperature, and mortality at sub-freezing temperatures. We did not find significant variation in SCP between populations, which averaged −22.6 ± 0.67°C. Chill coma temperature was lowest for thrips in the most northern North Carolina population (0.07 ± 0.18°C), which suggests local adaptation to winter temperatures may have occurred there. Sub-freezing mortality did not differ between populations and was low at 96 h exposures down to −8°C. At −12°C, mortality was high (58 ± 7%) in exposure durations as short as 6 h and nearly 100% mortality at 24 h. Cold winter temperatures are not likely to prevent establishment of A. andersoni throughout much of the southeastern USA where alligatorweed occurs but questions remain about factors that may limit thrips persistence in some areas where alligatorweed is submerged or senesced during winter months.