In the course of breeding from an original pair of N. nigroscutum, diploid ♀ ♀ (2n = 14), in addition to haploid ♀ ♀ (n = 7), were found by weighing the fourth generation of offspring. Diploid ♀ ♀ occurred only among the progeny of mated ♂ ♂, the progeny of virgins consisting solely of haploid ♀ ♀. Diploid ♀ ♀ are usually 20–30% heavier than their haploid brothers and are produced at the expense of sisters. The haploid ♀ ♀ mated readily but only 1 diploid ♀ out of 150 achieved successful copulation, as shown by the production of ♂ ♂. The ♂ ♂ produced were triploid (3n = 21} and as expected proved highly sterile. Although diploid ♀ ♀ have been known for about 45 years in some of the higher Apocrita, this is the first time they have been recorded in the primitive Symphyta. Pedigree analysis shows that the founding parents carried three complementary sex alleles, a, b, and c. Biparental heterozygotes, a/b, a/c, b/c, are ♂ ♂; biparental homozygotes, a/a, b/b, c/c, diploid ♀ ♀; and impaternate hemizygotes, a, b, c, haploid ♀ ♀.
Prepupae of Neodiprion sertifer (Geoff.) held in darkness at 21 °C undergo a short normal diapause if exposed as feeding larvae to long photoperiods, but have no diapause if reared in the larval stage under short photoperiods. If cocoons from short-day rearings are exposed to 10 °C instead of 21 °C, a small proportion of the prepupal larvae undergo the normal or short diapause, but the majority enter an intense or prolonged type of diapause which results in three clearly defined periods of adult emergence within the range of 160 to 800 days after cocoon spinning. Mortality increases directly with the prolonged cocoon periods associated with intense diapause at 10 °C and there is a progressive decrease in reproductive potential of the survivors. If cocoons are held at 29 °C normal diapause and morphogenesis are prolonged but there is no evidence that a state of intense diapause is induced. Mortality is extreme, however, and the reproductive potential of the survivors is greatly reduced.The implication of these findings is discussed in relation to prolonged diapause in nature, a factor critical to the assessment of the seasonal history and population dynamics of the insect.
Overwintering eggs of Porthetria dispar increase their capacity to supercool during exposure to non-lethal conditioning temperatures. Measurements of supercooling points of eggs collected in Quebec and Massachusetts indicate that the gradual movement of the insect north and west from the initial point of introduction into North America has not been accompanied by natural selection for a more cold-hardy population. The protection afforded eggs by cold-hardening is, however, greatly enhanced by the placement of egg masses, typically at or near ground level, where they are subject to maximum insulation by snow cover.Examination of climatic regimes within the current area of distribution of the gypsy moth in Eurasia indicates that temperature may not be a key factor limiting its northward spread. In central Canada, in the presence of abundant snow cover, the insect may spread as far north as suitable food plants exist. This would favour extension of the range of the gypsy moth throughout the Great Lakes – St. Lawrence Forest Region and much of the Boreal Forest Region of Ontario and Quebec south of James Bay.
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