Wbj

42 to the constituent sister groups [see Boudreaux (1979), Kristensen (1981, 1989, 1995),

Kukalova-Peck (1991,1998), Wheeler etal. (2001), Kukalova-Peck and Lawrence (2004)]. Currently, the most favored view is that the two primary sister groups are the neuropteroids + Coleoptera and the panorpoids + Hymenoptera (temporarily setting aside the status of the Strepsiptera), but it must be emphasized that the supporting evidence is not strong. Putative synapomorphies of the former group include the absence of cruciate ventral neck muscles, prognathous head with a gula, female genitalia, and campodeiform larva; those of the panorpoids + Hymenoptera are orthognathous head without a gula, eruciform larva with single-clawed legs, and ability to produce silk from labial glands. The majority of molecular phylogenetic analyses support this arrangement (see Wheeler, 1989; Wheeler etal., 2001).

The neuropteroid group includes three quite homogeneous orders—Neuroptera (lacewings), Megaloptera (alderflies and dobsonflies), and Raphidioptera (snakeflies)— which are sometimes included in a single order primarily on the basis of their very similar ovipositor (and the difficulty in determining good apomorphic characters for each). Neu-roptera and Megaloptera were already well established in the Permian and probably reached their peak diversity in the Triassic/Jurassic. Fossil Raphidioptera are not known until the Jurassic [reports suggesting their earlier existence are dubious according to Kukalova-Peck (1991)] and never reached the abundance of the other neuropteroids.

Remains of genuine Coleoptera (beetles) are known from the Upper Permian period. Somewhat earlier elytralike remains, originally thought to be from beetles, are now known to belong to the Protelytroptera (see above). Though some early paleontologists suggested that the Coleoptera had protorthopteran ancestors, implying at least a diphyletic origin for the endopterygotes, Crowson (1960,1981) and Kukalova-Peck (1991), among others, made a case for common ancestry with the neuropteroids. According to Crowson, this proposal is substantiated by the Lower Permian fossil Tshekardocoleus, which is intermediate in form between Coleoptera and Megaloptera. Crowson (1975) included Tshekardocoleus in the suborder Protocoleoptera, within the Coleoptera. Kukalova-Peck (1991), however, preferred to place it (and other beetlelike insects known from elytra in the same period) in a separate, probably paraphyletic order. The Coleoptera-neuropteroid sister-group relationship is strongly supported by the extensive analysis of Wheeler et al. (2001).

The position of the Strepsiptera (stylopoids), highly modified endoparasitic insects, remains controversial. The earliest fossils, from the Lower Cretaceous, are assignable to the extant family Elenchidae, so that speculation on their origin is based on comparative morphology. Kristensen (1981, 1989, 1991) has repeatedly noted that, based on the occurrence of instars with external wing buds and the carryover of larval eyes to the adult instar, the stylopoids could be considered exopterygotes. However, on the basis of many other features, they are unquestionably endopterygotes and on different occasions they have been allied with the panorpoids, Hymenoptera, and Coleoptera. Many authorities agree that the latter is the most likely arrangement, though opinions differ as to whether, for example, they are highly modified beetles [Crowson (1981) includes them as a family, Stylopidae, of Coleoptera] or are the sister order of the Coleoptera (Boudreaux, 1979; Kristensen, 1981; Kukalova-Peck, 1991, 1998; Kukalova-Peck and Lawrence, 1993, 2004). In support of the latter view the use of the hind wings only in flight and features of the hind wing venation are cited as synapomorphies. Other features taken to indicate a close association between the two groups are the extensive sclerotization of the sternum (rather than the tergum), the resemblance between the first instar larva of Strepsiptera and the triungulin larva of the beetle families Meloidae and Rhipiphoridae, and the similarity between the habits of en-doparasitic forms of Rhipiphoridae and those of Strepsiptera. By contrast, a number of

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment