Diapause completion in the almond seed wasp, Eurytoma amygdali (Hymenoptera : Eurytomidae) following early low temperature treatment

Abstract

Fruit of two almond, Primus amygdahis Linnaeus, cultivars (Retsou and Truoito) containing diapausing larvae of Eurytoma amygdali Enderlein, were collected in early August from coastal areas in northern Greece. Some larvae were removed from the fruit and maintained singly in open plastic vials and others left in the fruit until the end of the low-temperature period. They were kept at a low temperature of 10 degrees C from the beginning, or after 8 weeks at 20 degrees C. The larvae were subsequently maintained at 20 degrees C and whether they completed the two diapause stages was recorded for 60 more weeks. When the larvae in vials, were kept initially for 8 weeks at 20 degrees C, most of those from Retsou and all of those Truoito almonds completed the first stage of diapause. Of the larvae in the fruits, most of those in Truoito but less than 50% of those in Retsou almonds completed the first stage of diapause after 8 weeks at 20 degrees C. Larvae from different orchards and different almond cultivars differed in diapause intensity. When the larvae were kept at a low temperature of 10 degrees C from the beginning for 4, 8 or 16 weeks and then at 20 degrees C they completed the second diapause stage synchronously, but the time of completion was delayed, and depended on the duration of the low temperature treatment. In several cases the time to diapause completion was bimodally distributed and the relative size of peak depended on the duration of the early exposure to low temperature.