toxins Review The Mechanisms of Social Immunity Against Fungal Infections in Eusocial Insects Long Liu 1,2, Xing-Ying Zhao 1, Qing-Bo Tang 2, Chao-Liang Lei 1 and Qiu-Ying Huang 1,* 1 Hubei Insect Resources Utilization and Sustainable Pest Management Key Laboratory, Huazhong Agricultural University, Wuhan 430070, China;
[email protected] (L.L.);
[email protected] (X.-Y.Z.);
[email protected] (C.-L.L.) 2 Plant Protection College, Henan Agricultural University, Zhengzhou 450002, China;
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[email protected] Received: 29 March 2019; Accepted: 27 April 2019; Published: 29 April 2019 Abstract: Entomopathogenic fungus as well as their toxins is a natural threat surrounding social insect colonies. To defend against them, social insects have evolved a series of unique disease defenses at the colony level, which consists of behavioral and physiological adaptations. These colony-level defenses can reduce the infection and poisoning risk and improve the survival of societal members, and is known as social immunity. In this review, we discuss how social immunity enables the insect colony to avoid, resist and tolerate fungal pathogens. To understand the molecular basis of social immunity, we highlight several genetic elements and biochemical factors that drive the colony-level defense, which needs further verification. We discuss the chemosensory genes in regulating social behaviors, the antifungal secretions such as some insect venoms in external defense and the immune priming in internal defense. To conclude, we show the possible driving force of the fungal toxins for the evolution of social immunity.