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 A HISTORY OF CORNWALL CYNIPIDAE Gall-flies Most of the Gall-flies (Cynipidae) lay their eggs in the meristematic tissue of plants, chiefly, however, on the oak, and a secretion apparently from the larva itself causes an exuberant local growth of tissue that results in the formation of a gall. The oak apple, the oak spangle, the marble gall, and the moss-like bedeguar on the rose are familiar examples of such pathological growths. Some of the gall-flies, however, like the members of the genus Synergus are inquilines or guest-flies, laying their eggs in the galls formed by the gall-makers either during or subsequent to the growth of the gall. The typical cynipid gall-maker presents the remarkable anomaly of an alternation of generations, the autumn-formed gall producing females only, which by parthogenetic birth give rise to a spring brood of males and females. These last, as a rule, are only about one- third the size of their parent, and are very dissimilar in form of gall and in general appearance from the generation from which they arise. For thirteen species the galls both of the agamic and of the sexual generation have been found in Cornwall, and in the majority of cases the corresponding ' flies,' together with various inquilines and parasites, have been successfully raised. The process with many of the autumn-formed galls is long and tedious, some of them not appearing till the third year. Even more remarkable than this alternation of generations displayed by many of the species is the apparently complete absence of the male in Cynips Kollari and in Andruw albopunctatus. So far as can be ascertained, these species are propagated by perpetual parthenogenesis as only the agamic forms are known. Till five years ago this section of the Hymenoptera had received no attention in the county, but in the autumn of 1900 an appeal to the members of his agricultural class at the Technical Schools, Truro, resulted in a plentiful supply of galls of many kinds being brought in to the writer. To Commander Arthur Rogers, R.N.R., and to Mr. William Borlase, his thanks are specially due for the valuable services these skilled collectors so freely rendered in diligently searching out many of the rarer forms. The accompanying list of Cynipidae contains in all thirty-seven species. Where both broods of those that exhibit alternation of generations are known from actual observation to occur in the county, the specific names by which the two generations are still distinguished are bracketed together, the agamic generation in each case taking precedence : Rhodites eglanteriae, Htg. rosae, L. spinosissimae, Gir. Aulax glechomae, Htg. hypochaeridis, Kieffer Xestophanes potentillae, Vill. Periclistus caninae, Htg. Brandti, Ratz. Synergus melanopus, Htg. rheinhardi, Mayr radiatus, Mayr fascialis, Htg. thaumacera, Dal. - nervosus, Htg. Diastrophus rubi, Htg. Andricus ostreus, Gir. ( fecundatrix, Htg. { pilosus, Adler (Andricus globuli, Htg. inflator, Htg. f radicis, Htg. trilineatus, Htg. ' sieboldi, Htg. testaceipes, Htg. corticis, L. collaris, Htg. curvator, Htg. autumnalis, L. ramuli, L. quadrilineatus, Htg. ( callidoma, Gir. ( cirratus, Adler glandulae, Schenck solitarius, Fonsc. albopunctatus, Schlecht Cynips Kollari, Htg. JTrigonaspis renum, Gir. megaptera, Pz. (Biorhiza terminals, Fabr. ( aptera, Fabr. Dryophanta folii, L. divisa, Htg. longiventris, Htg. 'Neuroterus lenticularis, Oliv. , baccarum, L. fumipennis, Htg. tricolor, Htg. laeviusculus, Schr. albipes, Schr. numismatis, Oliv. vesicatrix, Schlecht ENTOMOPHAGA Ichneumons and their Allies The Ichneumon flies and their allies constitute Nature's most powerful check on the excessive increase of our insect population. Insects derive their sustenance very largely from the vegetable kingdom, and the destruction of all vegetation through the undue multiplication of phytophagous larvae like the Lepidoptera would be an ever-present danger but for the singular habits of this great family, every member of which is a parasite, dwelling in most cases in the body of a larval host, appropriating the nutriment the latter digests, and ultimately causing its death. The female ichneumons, as a rule, insert their eggs into the bodies of the selected larvae, and the resulting legless maggots during their development lie motionless in the dorsal half of their host, and either 176