Bionomics and Life History of a Filbert Leafroller, Archips rosanus (Lepidoptera: Tortricidae)1,2

Abstract

Field studies conducted in the Willamette Valley of Oregon 1973-1976 showed that overwintering eggs of Archips rosanus hatch in the last wk of March or the 1st wk of April. Egg hatch is spread over a 2 wk period. The median egg hatch was noticed at the accumulation of about 40 thermal units over a base of 8°C starting Jan. 1st. The young larvae move to the opening buds soon after hatching, and feed on leaves they have webbed together. Head capsule widths of the field-collected larvae indicate that there are 5 instars. Under field conditions, the 1st and 2nd instar larval periods vary from 2-3 wk. The first 2 instars make inconspicuous webbings and leaf rolls, but those of the 3rd, 4th and 5th instars are more noticeable. Their larval periods vary from 7-15 days each. Before pupation, the larvae go through a short pre-pupal period of 1-3 days. The pupae are formed within rolled leaves and are light brown at first changing to dark brown with age. The adults emerge within 1-2 wk after pupation, and are active only at night. Eggs are laid in masses, mostly on the trunks and major scaffold branches of the trees. The number of eggs in each mass ranges from 16-137, with an avg of about 50. Eggs of A. rosanus have an obligatory diapause which normally is broken by winter weather. Egg masses collected in March, 1976 and held in the laboratory at 26.7°C hatched within 6 days. Under laboratory conditions, the larvae went through 5 larval instars, but 7% went through 6, and the larval period varied from 10-20 days. The pupal period was about 1 wk. Adults lived for 10-12 days, and deposited an average of 147 eggs/female. The preoviposition period was about 2 days, the oviposition period 8 days, and the post oviposition period 5 days. Under field conditions, approximately ⅔ of the life cycle of A. rosanus was spent in the egg stage. The diapausing eggs were laid during June and July, and hatched in the following spring. Larvae were found in April and May, and pupae during the latter part of May and early June. Adults emerged during the 2nd half of June and early part of July, and were active until the 2nd wk of August. Reduced egg hatch (about 50%), and a high incidence of larval-pupal parasites were the 2 major mortality factors in untreated orchards. The major natural enemies of A. rosanus in the Willamette Valley include 2 tachinids, 1 pteromalid, 1 chalcid, 3 braconid, and 2 ichneumonid species.