58 



to attack in varieties of cultivated apples. Early ripening varieties 

 and those with sweet flesh or aromatic flavour seem to suffer most, 

 while of the first 12 varieties on the list in order of freedom from 

 infestation, 11 have a tough or a thick skin. Emergence of the adults 

 begins in the last week of June or the first of July, is at a maximum 

 in the second or third weeks of July, and is practically at an end by 

 the middle of August ; in New Hampshire there is no indication of a 

 second brood, and considerable evidence that none exists. The egg 

 is deposited shghtly beneath the skin of the fruit, sweet or aromatic 

 fruits being preferred. With a tree of a susceptible variety the only 

 factor of consequence determining the amount of infestation is the 

 relative abundance of females compared with the amount of fruit 

 available. Adult females normally exhibit a tendency to remain in 

 the immediate locality where emergence has taken place ; when 

 attractive fruit is not available, they are forced to disperse, but 

 apparently seldom travel more than a few hundred yards. The 

 results of extended trials of poison bait sprays and of poison trap 

 pans lead to the conclusion that the adults of R. fomonella are not 

 noticeably attracted to such substances as sugar, glucose, and 



The duration of the egg stage is from five to seven days, a mellowness 

 of the pulp being essential to the full development of the larva. The 

 length of the period between the dropping of the fruit and the exit 

 of the larvae is a matter of much importance economically, if control 

 measures are to be directed towards this phase of the life-cycle. For 

 this reason, part of the investigation was arranged with a view to 

 securing considerable data on the varying lengths of this period and 

 the factors that influence them. One table gives a list of varieties 

 studied, together with the ripening season of each, and ten others 

 detail the exit of larvae from dropped fruit. In apples of an early, 

 soft type, one-fourth of the larvae may issue by the end of the first 

 week after the apple falls. With early fruit of firmer flesh, less than 

 5 per cent, issue during the first week, the maximum occurring in the 

 third week. With autumn apples, 1 per cent, or less issue in the first 

 week, and in the second and succeeding weeks this depends on the 

 tendency towards rapid decay. With hard, winter fruit, a few larvae 

 may issue during the first four or five weeks. In most cases, larvae 

 issue more quickly from fruits that fall towards the close of the season 

 than from those falling early. In the case of winter fruit, few larvae 

 mature from fruits falling after the third or fourth week in September. 

 The great majority of the larvae issue at night. There is often a high 

 mortahty in the egg and larval stages of R. pomondla ; the average 

 observed was 64*2 per cent., but in late winter varieties the mortality 

 may reach 100 per cent. The duration of the larval stage may not 

 exceed about thirty days, or may be greatly prolonged, as in hard, 

 winter fruit. Mature larvae leave the fruit and pupate, normally, 

 in the soil, beneath or close to the apple, at a depth of one or two 

 inches. The duration of the pupal stage is variable, as this species ex- 

 hibits both a one-year and a two-year life-cycle ; in the former the 

 pupal stage occupies, approximately, 300 days. Some individuals, 

 both early and late maturing, require an extra year for the pupal 

 stage, and emergence of the adults from these pupae occurs at the 

 normal time in the second summer. , 



