Photoperiodic control of larval development rate inPlanotortrix excessana(Lepidoptera: Tortricidae): Evidence for larval diapause

Abstract

The larval development rate and pupal weights of Planotortrix excessana Walker were monitored under seven different 24 h photoperiods. Larvae developed through 5-7 instal's with the extra instars being most common in females. Photoperiod had a significant effect on the duration of all instars, total larval period, and number of instars.The response for both larval duration and instar number was typical of insects in which diapause occurs during long days. Evidence for the presence of a photoperiodically induceddiapause is discussed. Disturbance oflarvae during head-capsule measurement significantly reduced pupal weight in both sexes but had no effect on larval duration.

Effects of photoperiod and temperature on head-capsule size inPlanotortrix octo(Lepidoptera: Tortricidae)

“…Earlier studies on the New Zealand tortricid Planotortrix octo Dugdale have shown a photoperiodic response for larval duration and instar number, with larvae taking longer to develop and expressing a supernumerary 6th or 7th instar under short days (Morris 1990a). The shape of the response curve is similar to that found in long-day diapausing insects (Beck 1980).…”

“…The size of instars 1,3, and 6 are not recorded as tbe photoperiodic differences were not significant. However, tbese are recorded in a earlier paper, and tbe difference in head-capsule size between tbe 5 and 6 instar groups is statistically significant from tbe 3rd instar onwards (Morris 1990a).…”

“…These had originally been collected from Canterbury, New Zealand and reared in a laboratory since 1982 (Clare et al 1987). They were reared to pupation on General Purpose Diet (Singh 1983), as described by Morris (1990a).…”

“…The shape of the response curve is similar to that found in long-day diapausing insects (Beck 1980). The pupal weight (Morris 1990a) and pupal duration (Morris 1990b) also show a photoperiodic response, with intermediate length…”

Effect of temperature and photoperiod on pupal development rates inPlanotortrix octoDugdale* (Lepidoptera: Tortricidae)

“…Both of these are high during shortdays, with a sharp decline at long day photoperiods and a shallower decline in total darkness (Morris 1990a).…”