Hymenoptera Norman F Johnson, The Ohio State University, Columbus, OH, USA r 2013 Elsevier Inc All rights reserved Glossary Arrhenotoky Reproductive mode in which unfertilized eggs develop into haploid males and fertilized eggs develop into diploid females Eusociality Cooperative behavior among individuals of the same species characterized by reproductive division of labor, overlap of generations, and cooperative nesting Holometabola Insects characterized by complete metamorphosis, a wingless larval stage, and an intermediate pupal stage Idiobiont A parasitoid that develops on a paralyzed, incapacitated host Koinobiont A parasitoid that develops on a mobile, active host Monophyletic A group in which all species are descended from a single common ancestor and all descendants of the ancestor are classified in the group; characterized by shared derived characters The insect order Hymenoptera comprises a vast array of species that are familiar to even the most casual observer The group includes the ants, bees, and wasps as well as less wellknown groups such as the chalcids, ichneumons, sawflies, and the wood wasps Hymenoptera are extremely common on all the continents of the world, except Antarctica Hymenoptera range in size from microscopic species less than mm in length as full-grown adults to species in which the females are 10 cm or more in total body size Hymenoptera are holometabolous insects, generally characterized by mandibulate mouthparts, complete metamorphosis, and two pairs of membranous wings One striking feature is that the vast majority of species are characterized by arrhenotokous parthenogenesis: Fertilized eggs develop into diploid females and unfertilized eggs ultimately develop into haploid males Adult Hymenoptera generally feed on nectar, honeydew, or other sugar sources, but some are actively predaceous The larvae have a wider variety of feeding habits: Some feed on plants or fungi, whereas others feed on animals, as predators or parasitoids The larvae of bees and a few other groups feed on provisions of pollen collected and stored by the parent female The egg-laying appendages, the ovipositor, are often specialized to place the eggs on or into the plants or arthropods that will serve as the food source for the developing larvae In one large group, the Aculeata, the ovipositor is modified into the sting, a structure that primarily serves to deliver toxic venoms to paralyze the prey or is used in defense The Hymenoptera are also noteworthy for the evolution of social behavior in several groups The most highly developed form, eusociality, has arisen many times within the order among the bees, wasps, and ants Encyclopedia of Biodiversity, Volume Ovipositor Modified appendages of the seventh and eighth abdominal segments used for egg laying Paraphyletic A group in which only some of the species descended from an ancestor are classified together; characterized by shared ancestral characters Parasitoid An organism in which the immature stage feeds and develops on a single host arthropod, resulting in the death of the host Parthenogenesis Reproduction in which eggs are not fertilized by males Phylogeny Branching pattern of evolutionary relationships among organisms Phytophagy Plant feeding, herbivory Thelytoky Reproductive mode in which unfertilized eggs develop into diploid females Classification Hymenoptera has been traditionally divided into two suborders, the Symphyta and the Apocrita The Symphyta comprise the sawflies and wood wasps (Gauld and Bolton, 1988; Goulet and Huber, 1993; Hanson and Gauld, 1995; Naumann, 1991) The larvae of the vast majority of species in this suborder consume plant or fungal material, feeding on leaves or stems, feeding within galls produced in the host plant, or boring within stems or trunks of woody plants Symbiotic fungi comprise a significant part of the diet of many of the wood-boring species Sawfly larvae that feed externally on leaves are generally eruciform, i.e., caterpillar-like in form, with well-developed thoracic legs, abdominal prolegs, and sclerotized heads The suborder Apocrita descends from a symphytan ancestral species As adults, the first abdominal segment of the Apocrita is intimately associated with the thorax and separated from the following segments by a mobile constriction This segment is called the propodeum Thus, the locomotory tagma of the body, bearing the legs and wings, is four segmented The larvae are generally immobile and highly simplified in structure Apocrita are generally characterized by larvae that feed on other arthropods, including predatory species in which one larva feeds on several prey items and parasitoids in which the larva feeds on a single host individual Parasitoids are distinguished from parasites in that the host of the former is usually killed as a result of feeding Thus, ecologically, parasitoids function as predators, feeding on and ultimately killing their host The parasitoid life history is also found in the closest living relative of Apocrita within the Symphyta – the http://dx.doi.org/10.1016/B978-0-12-384719-5.00163-5 177