Early springtime water absorption by overwintering eggs of Mindarus abietinus (Hemiptera: Aphididae): possible implications for cold hardiness and diapause termination

Abstract

AbstractEggs of the balsam twig aphid Mindarus abietinus Koch (Hemiptera: Aphididae) overwinter for several months in obligate diapause, which terminates in early springtime when embryogenesis of the stem mother supposedly resumes. Important shape and size changes were observed on eggs collected at regular intervals during late winter and early spring. These observations led to the visual classification of eggs into three shape categories: flat eggs (C1), semi-flat eggs (C2), and round and turgid eggs (C3). Egg mass significantly increased with time during late winter and early spring, which coincided with the noticeable changes in morphological composition (i.e., from C2 to C3). Our observations suggest that free water surrounding eggs on fir (Abies balsamea (Linnaeus) Miller; Pinaceae) shoots is essential for M. abietinus normal embryonic development during snowmelt. Also, reduced egg water content during winter could modify its supercooling point, and the renewed availability of water in springtime may signal diapause termination and/or initiate embryogenesis of the stem mother.