Multivariate evaluation of cold tolerance in domestic and foreign populations for addressing climate mismatch in biological control of Alternanthera philoxeroides in the USA

Authors: KNIGHT, IAN - Us Army Engineer Research And Dvelopment Center; HARMS, NATHAN - Us Army Engineer Research And Dvelopment Center; Reddy, Angelica; Pratt, Paul

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2023
Publication Date: 11/15/2023
Citation: Knight, I., Harms, N.E., Reddy, A.M., Pratt, P.D. 2023. Multivariate evaluation of cold tolerance in domestic and foreign populations for addressing climate mismatch in biological control of Alternanthera philoxeroides in the USA. Entomologia Experimentalis et Applicata. 171(12):1019-1033. https://doi.org/10.1111/eea.13301.
DOI: https://doi.org/10.1111/eea.13301

Interpretive Summary: When the climatic tolerances of introduced biological control agents do not completely overlap with those of their host (i.e., climate mismatch), the result may be a gradient of inadequate control. The traditional approach to address climate mismatch is to return to the host’s native range to identify new climate-adapted agent species or biotypes. In addition, introduced populations that have sufficient climate tolerances could be used more widely in the invaded range. Alligatorweed is an invasive aquatic weed in California and the southeastern USA. A flea beetle was released throughout the 1960s and 70s, but the plant has remained a problem, especially at higher latitudes. To improve the control efficacy of the beetle in cooler parts of the USA, by introducing cold-hardy biotypes of the beetle, we conducted foreign and domestic exploration in parallel. We used multiple metrics (supercooling point, critical thermal minimum, and development/survival at low temperatures to compare cold tolerance 1) between foreign South American (SA) and domestic (i.e., introduced) North American (NA) populations and 2) among eight domestic NA populations collected throughout the southeastern USA. There were no differences in the supercooling point between SA and NA populations. However, SA populations had lower critical thermal minimum, a higher rate of survival to adulthood, and faster development times at colder temperatures than NA populations. This suggests that foreign exploration yielded substantially more cold tolerant biotypes of the beetle as compared to domestic populations in the USA. In the second study, significant variability in cold tolerance metrics was observed among the domestic NA populations, but there were no clear trends between population location (latitude) and performance, suggesting that it is unlikely that any of these populations are as well suited to temperate regions as those sourced directly from matched climates in their native range. Results of the comparison of cold tolerance between NA and SA beetle populations provide strong support for the use of traditional foreign exploration as a solution to climate mismatches.

Technical Abstract: When the climatic tolerances of introduced biological control agents do not completely overlap with those of their host (i.e., climate mismatch), the result may be a gradient of inadequate control. The traditional approach to address climate mismatch is to return to the host’s native range to identify new climate-adapted agent species or biotypes. In addition, introduced agent populations that have sufficient climate tolerances could be used more widely in the invaded range. Alligatorweed, Alternanthera philoxeroides, is an invasive aquatic weed in California and the southeastern USA. The alligatorweed flea beetle, Agasicles hygrophila, was released throughout the 1960s and 70s, but the plant has remained a problem, especially at higher latitudes. To improve the efficacy of A. philoxeroides in cooler parts of the USA, by introducing cold-hardy biotypes of A. hygrophila, we conducted foreign and domestic exploration in parallel. We used multiple metrics (Supercooling point (SCP), critical thermal minimum (CTmin), and development/survival at low temperatures) to compare cold tolerance 1) between foreign South American (SA) and domestic (i.e., introduced) North American (NA) populations and 2) among eight domestic NA populations collected throughout the southeastern USA. There were no differences in SCP between SA and NA populations. However, the CTmin of SA populations (1.37 °C) was 59.2% lower than NA populations (3.35 °C). Also, SA populations had a higher rate of survival to adulthood and faster development times at colder temperatures than NA populations, indicating that foreign exploration yielded substantially more cold tolerant biotypes of A. hygrophila as compared to domestic populations in the USA. Significant variability in cold tolerance metrics was observed among the domestic NA populations, but there were no clear trends between population location (latitude) and performance, suggesting that it is unlikely that any of these populations are as well suited to temperate regions as those sourced directly from matched climates in their native range. Results of the comparison of cold tolerance between NA and SA A. hygrophila populations provide strong support for the use of traditional foreign exploration as a solution to climate mismatches.