Modelling emergence of bronze beetle (<i>Eucolaspis</i> spp) adults using degreedays and threshold temperatures

Abstract

Eucolaspis spp beetles are native and endemic to New Zealand and are important pests of exotic fruit crops Organic apple orchards in Hawkes Bay seem to be particularly vulnerable and there adult beetles emerge during spring/summer feed on leaves and fruitlets and cause significant economic loss Seasonal variations in bronze beetle occurrence especially in adult emergence add further problems to already deficient control measures available to organic growers Phenological models that could predict adult emergence in the field would greatly benefit bronze beetle control programmes Pupal development was observed in bronze beetles at three constant temperatures (12 15 and 18C) in the lab and the lower threshold temperature (469C) and degreedays (237 degreedays) required for adult emergence from pupae were calculated using linear regression Adult emergence data obtained from other trials and from Plant Food Research were used to validate the thermal calculations A biofix date of the second week in September and horizontal degreeday calculation method using soil temperature (at 10 cm depth) gave best predictions Further research on thermal requirements of prepupal postdiapause larvae would augment these findings