Susceptibility of the Codling Moth to Diflubenzuron1

In tests with adults, eggs, and 1st instars of Laspeyresia pomonella (L.), only the eggs appeared to be susceptible to diflubenzuron. Young eggs less than 250°H (degree hours, base 10°C) old were most susceptible, but susceptibility declined with age. Significant mortality occurred also in 1st instars which hatched from eggs treated during the 1st half of the incubation period. In contrast, direct exposure of 1st instars to surface residues did not affect survival or subsequent development to the adult stage. Combined egg and 1st instar mortality averaged 91% if exposure occurred prior to the midpoint of egg development. Dosage-mortality curves were determined for eggs less than 250°H old which yielded LC50 values of 0.207 mg/liter for technical diflubenzuron and 0.437 mg/liter for the 25 WP. Diflubenzuron applied topically to adult moths caused no mortality, nor did it affect normal oviposition behavior or viability of the offspring. Under field conditions, residues on pear foliage remained active against codling moth eggs for atleast 6 weeks.