Of direct observations on the sexes of Lepidoptera, reared either from eggs or caterpillars, I have received only the few following cases: (See following table.)
So that in these eight lots of cocoons and eggs, males were produced in excess. Taken together the proportion of males is as 122.7 to 100 females. But the numbers are hardly large enough to be trustworthy.
On the whole, from these various sources of evidence, all pointing in the same direction, I infer that with most species of Lepidoptera, the mature males generally exceed the females in number, whatever the proportions may be at their first emergence from the egg.
Males Females The Rev. J. Hellins* of Exeter reared, during 1868, imagos of 73 species, which consisted of 153 137
Mr. Albert Jones of Eltham reared, during 1868, imagos of 9 species, which consisted of 159 126
During 1869 he reared imagos from 4 species consisting of 114 112
Mr. Buckler of Emsworth, Hants, during 1869, reared imagos from 74 species, consisting of 180 169
Dr. Wallace of Colchester reared from one brood of Bombyx cynthia 52 48
Dr. Wallace raised, from cocoons of Bombyx Pernyi sent from China, during 1869 224 123
Dr. Wallace raised, during 1868 and 1869, from two lots of cocoons of Bombyx yamamai 52 46
Total 934 761
(*83. This naturalist has been so kind as to send me some results from former years, in which the females seemed to preponderate; but so many of the figures were estimates, that I found it impossible to tabulate them.)
With reference to the other Orders of insects, I have been able to collect very little reliable information. With the stag-beetle (Lucanus cervus) "the males appear to be much more numerous than the females"; but when, as Cornelius remarked during 1867, an unusual number of these beetles appeared in one part of Germany, the females appeared to exceed the males as six to one. With one of the Elateridae, the males are said to be much more numerous than the females, and "two or three are often found united with one female (84. Gunther's 'Record of Zoological Literature,' 1867, p. 260. On the excess of female Lucanus, ibid, p. 250. On the males of Lucanus in England, Westwood,' 'Modern Classification of Insects,' vol. i. p. 187. On the Siagonium, ibid. p. 172.); so that here polyandry seems to prevail." With Siagonium (Staphylinidae), in which the males are furnished with horns, "the females are far more numerous than the opposite sex." Mr. Janson stated at the Entomological Society that the females of the bark feeding Tomicus villosus are so common as to be a plague, whilst the males are so rare as to be hardly known.
It is hardly worth while saying anything about the proportion of the sexes in certain species and even groups of insects, for the males are unknown or very rare, and the females are parthenogenetic, that is, fertile without sexual union; examples of this are afforded by several of the Cynipidae. (85. Walsh in 'The American Entomologist,' vol. i. 1869, p. 103. F. Smith, 'Record of Zoological Lit.' 1867, p. 328.) In all the gall-making Cynipidae known to Mr. Walsh, the females are four or five times as numerous as the males; and so it is, as he informs me, with the gall-making Cecidomyiidae (Diptera). With some common species of Saw-flies (Tenthredinae) Mr. F. Smith has reared hundreds of specimens from larvae of all sizes, but has never reared a single male; on the other hand, Curtis says (86. 'Farm Insects,' pp. 45-46.), that with certain species (Athalia), bred by him, the males were to the females as six to one; whilst exactly the reverse occurred with the mature insects of the same species caught in the fields.