Budbreak phenology and natural enemies mediate survival of first-instar forest tent caterpillar (Lepidoptera : Lasiocampidae)

Synchrony of egg hatch with budbreak has been proposed as an important comp onent in the population dynamics of many spring feeding forest Lepidoptera. Here, ne examine the consequences of phenological asynchrony with the budb reak of trembling aspen (Populus tremuloides Michaux) for cohorts of forest tent caterpillar, Malacosoma disstria Hubner, larvae in north central Albe rta Canada. The timing of eclosure was adjusted through temperature exposur e in the laboratory so that pairs of hatching egg bands were placed on tree s belonging to a single aspen clone at intervals beginning 2 d before and a t 2, 6, 10, and 18 d after budbreak. On each tree, 1 egg band was protected from predation with a sleeve cage and the other was left unprotected, Larv ae from later hatching cohorts required significantly more calendar days an d nearly 3 times as many degree-days to complete the 1st instar as did thos e hatching in synchrony with budbreak. Survivorship of later hatching cohor ts was reduced drastically by invertebrate predation in unprotected groups but no change in overall survival was recorded for protected groups, sugges ting that protracted development times caused by declining foliar quality e nhanced the success of natural enemies. We hypothesize that a narrow phenol ogical window ill host quality after budbreak and its interaction with natu ral enemies has exerted strong selective pressure on larvae to emerge from eggs as early as possible in the spring and that this window is a potent fo rce in determining the dynamics of low density populations of tent caterpil lars.