The thermal physiology of Lysathia sp. (Coleoptera: Chrysomelidae), a biocontrol agent of parrot’s feather in South Africa, supports its success

ABSTRACT

The establishment success of biocontrol agents originating from tropical regions is often limited by climate when introduced in temperate regions. However, the flea beetle, Lysathia sp. (Coleoptera: Chrysomelidae), a biocontrol agent of Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae) in South Africa, is an effective agent in regions where other biocontrol agents of tropical aquatic weeds have failed due to winter-induced mortality. The development (degree-day model) and thermal tolerance (critical thermal minimum/maximum [CT_min/max] and lower/upper lethal limits [LLT/ULT₅₀]) of Lysathia sp. were investigated to explain this success. The model predicted that Lysathia sp. could complete 6 to 12 generations per year in the colder regions of the country. The lower threshold for development (t₀) was 13.0 °C and thermal constant (K) was 222.4 days, which is considerably lower than the K values of other biocontrol agents of aquatic weeds in South Africa. This suggests that above the temperature threshold, Lysathia sp. can develop faster than those other species and complete multiple life cycles in the cooler winter months, allowing for rapid population growth and thus improving M. aquaticum control. Furthermore, the CT_min of Lysathia sp. was 2.3 ± 0.2 °C and the CTmax was 49.0 ± 0.5 °C. The LLT₅₀ was calculated as ∼ −7.0 °C and the ULT₅₀ as ∼ 43.0 °C. These wide tolerance ranges and survival below freezing show why Lysathia sp. has established at cool sites and suggest that it may be a suitable agent for other cold countries invaded by M. aquaticum.

KEYWORDS:

• Myriophyllum aquaticum
• degree-day model
• thermal tolerance
• critical thermal limits
• lethal temperatures

Acknowledgements

The authors thank the Natural Resources Management Programme of the Department of Forestry, Fisheries and Environmental Affairs, South Africa for funding this research. Further funding for this work was provided by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa. We also thank the anonymous reviewers whose valuable feedback improved the manuscript greatly. Any opinion, finding, conclusion or recommendation expressed in this material is that of the authors and the NRF does not accept any liability in this regard.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Department of Forestry, Fisheries and Environmental Affairs, South Africa: [Natural Resources Management Programme]; Department of Science and Technology and the National Research Foundation [South African Research Chairs Initiative].