Safranek Louis, Williams Carroll M
Biol Bull. 1984 Dec;167(3):568-578. doi: 10.2307/1541410.
Hornworm larvae adhere to Dyar's rule under normal growth conditions, increasing their live weight by an average of 5- to 6-fold from the outset of one instar to the next. This adherence to Dyar's rule is largely maintained even in instars subsequent to those in which larvae have been severely malnourished. The importance of relative weight gain for the normal onset of larval molting contrasts with the requirement for attainment of an absolute body weight prior to pupation. But body size is by no means the sole cue for the initiation of a larval molt. Thus, under conditions of malnutrition larvae can initiate a molt at any weight and can do so even in the absence of any weight gain in an instar: in these circumstances the duration of an instar is inversely related to the weight at the outset of malnutrition. In larvae fed ad lib as well as in malnourished larvae the initiation of a molt appears to be limited to a discrete phase of the photocycle. The failure of larvae to molt on schedule at body weights lower than those predicted by Dyar's rule cannot be attributed to an inability of the brain to stimulate ecdysone-dependent development as is the case in diapausing pupae. Though body size, instar duration, and photocycle all interact to determine the onset of the molt, the role of the brain remains ill-defined.
在正常生长条件下，烟草天蛾幼虫遵循戴尔法则，从一个龄期开始到下一个龄期，其活体重平均增加5至6倍。即使在幼虫严重营养不良后的龄期，这种对戴尔法则的遵循在很大程度上仍然保持。幼虫蜕皮正常开始时相对体重增加的重要性与化蛹前达到绝对体重的要求形成对比。但体型绝不是幼虫蜕皮开始的唯一线索。因此，在营养不良的情况下，幼虫可以在任何体重时开始蜕皮，甚至在一个龄期没有体重增加的情况下也能这样做：在这些情况下，一个龄期的持续时间与营养不良开始时的体重成反比。在自由采食的幼虫以及营养不良的幼虫中，蜕皮的开始似乎都局限于光周期的一个离散阶段。幼虫在低于戴尔法则预测体重时未能按时蜕皮，不能归因于大脑无法刺激依赖蜕皮激素的发育，就像滞育蛹的情况那样。尽管体型、龄期持续时间和光周期都相互作用以决定蜕皮的开始，但大脑的作用仍然不明确。
