Ecological mechanisms and prospects for utilization of toxins from parasitic hymenopterans

Abstract

Insects in the order Hymenoptera defend themselves, attack prey and regulate hosts using toxins that are effective in small quantities. In this study, advances in the researches on parasitic hymenopteran toxins are summarized in terms of the production, categories, components, properties, ecological functions and mechanisms. The glands that produce venoms derive from the ectoderm tissue and evolve from the accessory glands of the reproductive system. Venoms are excreted by the poison gland or acid gland of mature female wasps and stored in reservoirs. The components of insect toxins are very complicated, and hymenopteran venoms contain alkanes, alcohols, aldehydes, ketones, organic acids, esters, lactones, proteins, polypeptides, enzymes, amines and other compounds. Toxins of parasitic hymenoptera play an important adaptive role. They can increase the probability of successful oviposition by paralyzing hosts, enhancing offspring survival by inhibiting host development and immunoreaction, and improving the nutrition available for their progeny by disturbing the hosts’ physiological response. Venoms of the ectoparasitoids often lead to arrested development, permanent paralysis and even death of hosts. These toxins are usually broad-spectrum and act on the central nervous system or at the neuro-muscular junction. While most endoparasitoids are koinobionts, these parasitoids can regulate the physiology and development of the hosts, but no longer paralyze the hosts permanently. Also, they kill the hosts in a concealed but safe position after the hosts cocoon or build their pupal cells. Venoms of koinobiont parasitoids can contain polydnaviruses (PDV) that regulate the growth and development of the hosts by inhibiting the immune system and influencing the metamorphosis of hosts. Thus, PDVs are commensal and mutualistic, but non-pathogenic, with parasitoids at the molecular level. Promising prospects for the utilization of insect toxins, especially as medicines or specific bioinsecticides, are discussed. Because insect toxins are mixtures of complex ingredients and are usually produced in small quantities, isolation and purification of all the ingredients with bioactivity are needed for biochemical and toxicological research and for practical application.