EFFECTS OF INTENSITY AND DURATION OF LOW TEMPERATURES IN REGULATING DIAPAUSE DEVELOPMENT OF THE CABBAGE ROOT FLY (DELIA RADICUM)

Abstract

Low temperature was shown to be the major factor regulating diapause development of the cabbage root fly. Diapausing pupae had to be subjected to temperatures of from 0°—6° for 22 weeks for all individuals in the population to complete diapause development. Once this was complete, pupae required a further 14 days at 20° for most of the flies to emerge. Flies that emerged within 14 days at 20°, the criterion for diapause completion, were classed as early‐emerging. The percentage of early‐emerging flies gradually increased as the period of low temperature was extended from 12 to 22 weeks. In the range 0° to 10°, parallel linear relationships were established between the logarithm of the duration of the low temperature and the probit of the percentage of early‐emerging flies. The lower the temperature between 0° and 10°, the more effective it was in terminating diapause. Populations of pupae from nine different localities in England and Wales all took the same time (22 weeks) to complete their low‐temperature diapause development. There was no indication that this rate of development was affected by light, photoperiod, diurnal temperature fluctuations or latitude. RÉSUMÉ Effets de l'intensité et de la durée du froid sur l'évolution de la diapause de la mouche du chou Des pupes de moches du chou élevées en laboratoire et en état de diapause durent ětre soumises à un froid de 4° pendant au moins 12 semaines, puis portées à 20°, avant qu'il ne soit possible à des mouches de sortir dans les 14 jours. On a dit des mouches apparues dans les 14 jours à 20° qu'elles sont apparues tǒt. La proportion de mouches apparues tǒt est devenue graduellement plus importante au fur et à mesure que le traitement froid a été porté de 12 à 22 semaines. Lorsque des pupes en diapause ont été soumises à une température constante de 0 à 10°, l'évolution de la diapause s'est faite plus rapidement aux températures les plus basses. Pour chaque température d'essai on a établi des rapports linéaires entre le logarithme de la durée du traitement froid et le probit du pourcentage de mouches apparues tǒt. Il a été confirmé que 6° est le seuil de morphogenèse de post‐diapause pour les mouches apparues tǒt. Des pupes ont été ramassées en 9 endroits en Angleterre et au Pays de Galles de novembre 1980 à janvier 1981, elles ont été conservées à 4° et toutes avaient terminé leur diapause le 9 mars. Toutes les générations F1 des populations ont réagi aux températures de 0 à 10° de manière analogue aux populations de Wellesbourne, l'évolution de la diapause étant terminée dans 84–91% des populations F1 au bout de 19 semaines à 4°.

Emergence Patterns of Delia radicum (Diptera: Anthomyiidae) Populations from North Carolina and New York

“…Diapausing pupae were then collected from the rutabaga, stored at 4°C and a photoperiod of 8:16 (L:D)h for a minimum of 16 wk to complete diapause development, and then placed at 20°C and a photoperiod of 16:8(L:D)h and fly emergence recorded daily. Although Collier & Finch (1983) reported that 20 wk was necessary for completion of diapause development for D. radicum populations in England, flies emerged from 80% of pupae collected in our studies, indicating that our population required a shorter cold treatment than the Collier & Finch (1983) population for completion of diapause development.…”

“…In Finch & Collier's (1983) In view of the later emerging characteristics of progeny from the L x L crosses compared with all other crosses (Fig. 1), it seems possible that a late-emerging biotype could easily evolve from this intermediate biotype if early emergers were removed from the population.…”

“…In addition, an intermediate biotype was also described that consisted of different proportions of individuals with slightly later emergence, but tending more toward the early than late spectrum of emergence (Finch et al 1986). Finch & Collier (1983) also demonstrated that populations exhibiting early-, intermediate-, or late-emergence patterns could be selected within one generation from a parental population that was heterogeneous with respect to emergence. The dominance of either early-or lateemerging biotypes in various localities was presumed to be maintained by temporal, and thus reproductive, isolation (Finch et al 1986).…”

“…Finch & Collier (1983) found that in some areas of the United Kingdom spring emergence occurred over a relatively short period of time in April or May, whereas in other areas emergence was protracted such that many flies did not emerge until June or July. These different populations were classified as early-and late-emerging biotypes based on the timing of spring emergence.…”

“…These earlier studies in North Carolina (Fulton 1942) were conducted before Finch & Collier (1983) reported D. radicum biotypes that varied in spring emergence patterns. Finch & Collier (1983) found that in some areas of the United Kingdom spring emergence occurred over a relatively short period of time in April or May, whereas in other areas emergence was protracted such that many flies did not emerge until June or July.…”