BiJOODs. 33 



slioiild get our caterpillars a})pearing' on the same day and a uniform 

 succession of broods throug-lumt the active period. This is not the case, 

 and though the first brood of caterpillars may come at one time, the 

 later ones become irregular. We may take, as an instance, a moth having 

 a life history period from egg to moth of six weeks ; if Ave get the moths 

 out on March the 4th, the eggs are laid by March the 10th, the cater- 

 pillars appear, say, by March the 15th, become pupae about April the 

 15th and moths about the 22nd April. We find caterpillars again about 

 the beginning of May ; later broods of caterpillars would, if food were 

 available, come about the middle of June and the end of August, and 

 the caterpillars of the middle of October would hibernate ; there would 

 thus be outbreaks of the caterpillar in the latter half of March, begin- 

 ning of May, latter half of June, beginning of September and latter half 

 of October ; five attacks of this pest in all if food is abundant and all 

 come out together. Actually this rarely if ever occurs, but one can in some 

 cases trace the broods through the year and expect them at their regular 

 dates. In most cases the imagines do not all emerge together and the 

 subseq^^ent irregularity of development of the individuals accounts for 

 the irregularity of the broods. The appearance of large numbers of a 

 particular insect at regular intervals can be accounted for if one traces 

 its history and knows when it emerged from hibernation. We must, 

 however, guard against expecting regular broods ; it is often stated that 

 a particular pest has, say, four broods a year ; actually it is found 

 throughout a long* period, some being late, some early, some at the 

 proper time. The four broods are not regular, and though the insect 

 does breed four times in the year, all do not breed at the same time. 



