1. Four groups of spruce budworm larvae, Choristoneura fumiferana, of the same physiological stage (at the beginning of diapause) were exposed to natural temperatures, starting in July, August, September and October. Post-diapause emergence and certain metabolites were monitored throughout the overwintering period.2. Larval exposure to high temperatures for long periods before winter had a significant effect on temperature requirements for subsequent diapause development and apparently caused a certain amount of mortality, especially for those larvae that entered diapause earlier in the season.3. Substantial loss of lipid and glycogen reserves was related to intensity of high temperature exposure during the pre-winter period, which in turn was associated with the timing of diapause initiation.4. Patterns of glycerol accumulation during the winter were also influenced by temperature conditions in the early phase of diapause development.5. Among several possible mortality factors, an extended cool period in spring was suggested as a potential cause of overwintering mortality, which was closely associated with a deficiency in energy reserves caused by high temperature exposure before winter.6. These results stress the significant impact of pre-winter conditions on the overwintering process and highlight the importance of an ecophysiological approach to insect overwintering biology.

The Canadian Entomologist 125: 101 1-1021 (1993) The distribution of feeding damage by adult Phyllotreta cruciferae (Goeze) was examined on the cotyledons, first true leaves, stems, and petioles of four crop species of Brassicaceae (Brassica juncea L. "Cutlass", B. napus L. "Westar", B. rapa L. "Tobin", and Sinapis alba L. "Ochre"). Previous studies showed that B. napus and B. rapa are susceptible, B. juncea is partially resistant, andS. alba is highly resistant to P. cruciferae. Flea beetles usually fed more on the upper surfaces, bases, and edges of cotyledons and first true leaves, but the feeding patterns were not identical on the four species. Phyllotreta cruciferae had a greater preference for the upper surface of S. alba cotyledons than for the upper surfaces of Brassica species. First true leaves of B. napus had over 90% of the feeding damage along the edge, compared with <70% for the other species. The size of feeding pits did not differ on the upper and lower surfaces of the cotyledons and first true leaves for the Brassica species, but S. alba had smaller feeding pits on the lower surface. Sinapis alba also had the smallest feeding pits on the upper surface of its cotyledons, and S. alba and B. juncea first true leaves had feeding pits about one-half the size of the feeding pits on the other species. There was no significant difference in the amount of stem damage for the four species, but B. juncea had significantly less petiole damage than S. alba. Although there were differences in the way P. cruciferae exploited the seedling tissues of these Brassicaceae, the differences were not consistent with, or were too small to account for, the different levels of resistance of the four crops. Brandt, R.N., et R.J. Lamb. 1993. Dommages causes par 1'Altise des crucifkres Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae) sur les jeunes pousses de colza et de moutarde et rksistance des plantes. The Canadian Entomologist 125: 101 1-1021. THE CANADIAN ENTOMOLOGIST November/December 1993 pousses de ces Brassicaceae, mais ces diffkrences ne sont pas relikes de fagon systkmatique h la rCsistance des espbces ou alors elles ne sont pas assez importantes pour expliquer la variation de la rksistance. [Traduit par la rkdaction]

Spruce budworm larvae, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), in early-, mid-and latediapause (maintained at 2 ~ were exposed to various sub-zero temperatures, above the supercooling point, for different periods to determine the insect's cold-hardiness in terms of non-freeze survival. Larvae which were in the middle of diapause showed the highest survival (percentage of larvae emerging from hibernacula after diapause), followed by larvae in late-and early-diapause respectively. When exposed to -23 ~ larvae which were acclimatized to outside air temperatures had a much higher survival than the larvae maintained at 2 ~ This survival was correlated with a glycerol content that was ten times higher and a depressed supercooling point in acclimatized larvae compared to lab-maintained larvae. Experiments also demonstrated that mortality of the larvae maintained in an extended supercooled state at -23 ~ was due to cold injury rather than freezing. The present study supports the hypothesis that glycerol may have a cryoprotective role other than depressing the supercooling point in freeze-intolerant insects and highlights the importance of investigating non-freeze mortality during insect diapause.

The pre‐calling period (PCP), between emergence and first release of pheromone, determines the number of nights over which female Mythimna separata (Walker) (Lepidoptera: Noctuidae) can express their migratory potential. In its seasonal migrations in eastern Asia, this armyworm penetrates to latitudes at which it is unable to over‐winter but at which reliable photoperiodic and temperature cues anticipate the deterioration of conditions. The effect of these environmental factors on PCP was examined in moths descended from samples collected in Nanjing (32oN) during the summer migration. Under LD 14:10h, a reduction in temperature, from 23oC during larval development to 18oC from 24 h after pupation, resulted in a twofold increase in PCP compared with insects held at 23oC. At 23oC, short days (LD 12:12 h) extended PCP but the magnitude of the response was increased under a regime of decreasing photoperiod, from LD 15:9h, to LD 12:12 h through larval, pupal and adult development. Further experiments demonstrated that the response depended on a decrease in photoperiod from pre‐pupal stage to adult emergence (the pupal period is spent below ground). A reduction of 50–60min over the 13–15 day pupal period at 23oC was effective. The significance of decreasing photoperiods, irrespective of absolute levels, as a cue for species whose migrations traverse substantial ranges of latitude is considered and the results are discussed in relation to the genetic determination of PCP in M.separata and to its seasonal migrations in eastern China.

Migration in insects usually occurs prereproductively so the precalling period, between emergence and the first release of pheromone, determines the number of nights over which females of migrants such as Mythimna separata can express their migratory potential. Precalling periods (PCP's) ranged from 3 to 21 nights in F females from insects collected in the field in eastern China. As technical problems precluded the use of a sib-analysis design, the genetic basis of this variation was investigated by analysis of the correlation between daughters' and mother's PCP's and by selection in isofemale lines followed by reciprocal crosses. The results of these analyses indicated that PCP is strongly influenced by genes located on the X chromosome, inherited from the male parent in Lepidoptera. Genetic regulation of migratory potential, of which PCP is a crucial component, can be expected to evolve in tropical species such as Mythimna separata, whose larval habitats are associated with unpredictable tropical rainfall. This species has no preimaginal diapause but makes regular seasonal incursions every spring and early summer to high temperate latitudes at which it cannot overwinter. Where migrants are carried by winds, as occurs in these migrations, the predominantly poleward winds at this time of year must create a genetic cline across latitude, in which migratory potential of the summer populations founded by the migrants increases with increasing latitude. We suggest that X-linkage of genes influencing PCP may reduce the genetic load associated with this polymorphism by reducing the frequencies of inappropriate PCP genotypes in these summer populations. Thus, in autumn when winds are predominantly northerly, fewer individuals at any latitude will lack the capability to make the return journey southward. Some support for this model is provided by the observed distributions of PCP's of F females from moths collected in the field in central and northern eastern China. If X-linkage of genes influencing PCP contributes to the stability of these migratory cycles, it can be expected in other species with similar migratory strategies.

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One of the most damaging insect pests in deciduous forests of North America is the forest tent caterpillar, Malacosoma disstria Hübner. It can feed on a variety of plants, but trembling aspen (Populus tremuloides Michaux) is its preferred host and sugar maple (Acer saccharum Marshall) serves as a secondary one in the northern part of its distribution. Because host plant characteristics influence insect performance and survival, we evaluated the impact of trembling aspen and sugar maple foliage on M. disstria performance. Host effects on insect cold hardiness and overwintering survival of offspring were also studied. Forest tent caterpillar reared on aspen leaves had a shorter development time, higher pupal weights and fecundity, and superior egg parameters (length and weight) compared with those reared on sugar maple leaves. Larvae from the two food treatments had low glucose levels during diapause, whereas glycerol content of insects reared on maple was significantly higher during diapause than larvae fed on aspen. Lower glycerol content may explain the higher overwinter mortality of pharate larvae from aspen-reared parents even though their supercooling points were as low as -36 degrees C. This study shows the influence of host plant on insect life history and the need to consider overwintering success and offspring performance in studies to understand and predict population growth and cycling.