Changes in Diapause Response to Photoperiod in Laboratory Strains of Oriental Fruit Moth1,2

A colony of Grapholitha molesta (Busck) (Lepidoptera: Olethreutidae) has been maintained continuously on thinning apples at 27°C in the laboratory at Geneva, N. Y. Diapause has been prevented by continuous artificial lighting. During late 1957 and early 1958 the strain had a 96% diapause response to an 8:16-hour light:dark (LD) photoperiod compared with 1% 16:8 LD. Five years later (about 60 generations) the responses to 8:16, 12:12, and 16:8 LD were 2.7, 2.7 and 0.1%, respectively. A strain of oriental fruit moth from Vineland, Ontario, Canada, diapaused 96% at 12:12 LD, and 0.3% at 16: 8 LD, when reared in the same rooms. Starting in 1963, mass selection for nondiapause in the Vineland strain of oriental fruit moth was conducted for 31 generations under conditions of 27°C and a 12:12 LD photoperiod. Each generation was produced from the nondiapausing segment of the preceding generation. The percent diapause response fell from the original 96% to less than 1% by the 24th generation and remained at zero to less than 1%, thereafter. A field-collected strain diapaused normally under these same conditions.