The supercooling responses of the solitary bee osmia excavata (Hymenoptera: Megachilidae) under the biological stress of its brood parasite, sapyga coma (Hymenoptera: Sapygidae)

Authors: YAN, ZHUO - CHINESE ACADEMY OF SCIENCES; WANG, LINA - INSTITUTE OF ZOOLOGY - CHINA; Reddy, Gadi V.P.; GU, SHIMIN - INSTITUTE OF ZOOLOGY - CHINA; MEN, XINYUAN - SHANDONG ACADEMY OF AGRICULTURAL SCIENCES; XIAO, YUNLI - INSTITUTE OF ZOOLOGY - CHINA; GE, FENG - INSTITUTE OF ZOOLOGY - CHINA; OUYANG, FANG - INSTITUTE OF ZOOLOGY - CHINA; SU, JIANWEI - CHINESE ACADEMY OF SCIENCES

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2022
Publication Date: 2/27/2022
Citation: Yan, Z., Wang, L., Reddy, G.V., Gu, S., Men, X., Xiao, Y., Ge, F., Ouyang, F., Su, J. 2022. The supercooling responses of the solitary bee osmia excavata (Hymenoptera: Megachilidae) under the biological stress of its brood parasite, sapyga coma (Hymenoptera: Sapygidae). Insects. 13(3):1-11. https://doi.org/10.3390/insects13030235.
DOI: https://doi.org/10.3390/insects13030235

Interpretive Summary: Overwintering animals, especially insects, have evolved several different strategies to adapt to low-temperature environments in winter. Insects engaged in freeze-avoidance, continuously remove ice nucleators, which can initiate ice information when the ambient temperature is below the melting point. Insects engaged in freeze-avoidance keep body fluids liquid by synthesizing antifreeze proteins and lowering the crystallization temperature through the accumulation in tissues of sugars and polyols. Supercooling polymorphisms might exist in other insect species, helping them also overwinter more successfully. The type of overwintering strategy and the level and number of supercooling points are influenced by extrinsic and intrinsic factors. The underlying reason for the appearance of different supercooling types in any particular species is ultimately unclear but is a suitable subject for further study. In the longer run, we believe that the ideas present in this paper may have wider application to explore the overwintering strategies more deeply. In our study, the phenomenon of multiple supercooling processes (polymorphism of supercooling) was found in both the solitary bee and its brood parasite, following analysis of large numbers of individuals.

Technical Abstract: Many insects have evolved different strategies to adapt to subzero temperatures. It’s valuable to explore the underlying mechanism of insect cold resistance. However, the intraspecific difference of overwintering capacity in the same microhabitat has not been sufficiently investigated. This study assessed the overwintering cold tolerance traits of two insects, the solitary bee Osmia excavata Alfken and its brood parasite, Sapyga coma Yasumatsu & Sugihara. We measured 4035 samples (one individual as one sample) and discovered polymorphisms in the supercooling mechanisms in the above solitary bee and its brood parasite. We classified individuals based on the number of supercooling mechanisms they exhibited into four types, having, respectively, 1, 2, 3, or 4 types of supercooling processes. Most females (55.8%) and males (46.2%) of O. excavata were type ', while in the parasite S. coma, each sex was even more highly dominated by one mechanism (type 1): females (94.9%) and males (94.2%). Significant differences in the supercooling point were found between O. excavata (female: -24.10 ± 3.26 '; male: -23.59 ± 3.71 ') and S. coma (female: -21.59 ± 4.50 '; male: -19.88 ± 4.77 '). Females of both species had lower supercooling points and larger nutritional reserves than their corresponding males. Notably, the lowest supercooling point of individuals with several supercooling processes was lower than that of individuals with fewer supercooling processes. Our results suggest that O. excavata, which had a lower supercooling point and more supercooling mechanisms, may have a better capacity to survive a cold winter than its brood parasite, suggesting the supercooling polymorphisms may increase the chance of insect survival. Our findings provide new insights into overwintering strategies and supercooling points. The polymorphism we observed for supercooling mechanisms may provide a new framework for studying overwintering strategies.