The DNA sequence phylogeny splits Sorghum into two lineages, one comprising the 2n = 10 species with large genomes and their polyploid relatives, and the other with the 2n = 20, 40 species with relatively small genomes. An apparent phylogenetic reduction in genome size has occurred in the 2n = 10 lineage. Genome size evolution in the genus Sorghum apparently did not involve a 'one way ticket to genomic obesity' as has been proposed for the grasses.
Using flow cytometry, the genome sizes of two species of Strepsiptera were studied: that of male Caenocholax fenyesi texensis Kathirithamby & Johnston (Myrmecolacidae) at 108 Mb, which is the smallest insect genome documented to date; and those of male and female Xenos vesparum Rossi (Stylopidae), which are 1C = 130 and 133 Mb, respectively. The genome sizes of the following were analysed for comparative purposes: (a) the Hessian fly, Mayetiola destructor (Say), which was previously reported to be the smallest among insects: the male measured at 1C = 121 Mb and the female at 1C = 158 Mb; and (b) the female parasitic, haplodiploid, microhymenopteran wasp, Trichogramma brassicae Bezdenko, which measured at 1C = 246 Mb. The hosts of the strepsipterans were also measured: male Solenopsis invicta Buren, the red imported fire ant (host of male C. f. texensis), which is 1C = 753.3 Mb, and female Polistes dominulus Christ, the paper wasp (host of X. vesparum), is 1C = 301.4 Mb. Endoreduplication (4C) of the genome of the thorax of the male strepsipteran, and higher levels of endoduplication (4, 8, 16C) in the body of the larger female was observed. In contrast, little or no endoreduplication was observed, either in the Hessian fly, or in the parasitic wasp.
We report here the case of a metazoan parasite, a strepsipteran, that manipulates host epidermal tissue and wraps itself within it; which probably camouflages the endoparasite and is recognized as ''self'' by the host. This mechanism is one of immune avoidance among parasitoid insects. The host-derived epidermal ''bag'' might have enabled Strepsiptera to radiate to disparate hosts compared with the relatively few taxa (596 species) described so far. They have been recorded as parasitizing 34 families belonging to seven orders of Insecta. We also report a mechanism of insect ecdysis between the first-and second-instar larva, while enclosed in the bag.
Strepsiptera (Insecta), often referred to as 'stylops,' are curious entomophagous parasitoids of cosmopolitan distribution. They are curious not only for their biology but also for their host-parasitoid relationships. Kathirithamby (1989) reports that Strepsiptera are parasitic in members of seven insect orders (Thysanura, Blattodea, Mantodea, Orthoptera, Hemiptera, Hymenoptera and Diptera). The order Strepsiptera is divided into two suborders: Mengenillidia and Stylopidia (Kinzelbach 1971).Strepsiptera have only two free-living stages: the small, active adult winged male and the 1 st instar larva. The adult males have prominent compound eyes, elegantly branched antennae, 'haltere-like' forewings, and fan-shaped hind wings. They are shortlived (some live for only two hours), they do not feed, and a breeding flight is their sole mission. With the exception of the family Mengenillidae, the bizarre adult females are neotenic. Female Mengenillidae pupate outside their host, while female Stylopidia remain permanently endoparasitic; therefore, one must look for the host to find Stylopidia females. Strepsipteran females produce viviparous 1 st instar larvae, which emerge via the brood canal opening/opening of the apron (Kathirithamby 2000) in the cephalothorax of the endoparasitic female. In endopterygote
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