Emergence patterns of adult citrus gall wasp, Bruchophagus fellis (Hymenoptera: Eurytomidae), and its key parasitoids in southern Australia

•Citrus gall wasp emergence is highly synchronised.•Our degree-day model predicts peak emergence with an accuracy of ± 4 days.•Citrus gall wasp parasitoids emerge 2-3 weeks after citrus gall wasp.

Emergence of adult citrus gall wasp (CGW) Bruchophagus fellis (Girault) (Hymenoptera: Eurytomidae) in citrus orchards in far western New South Wales, Australia, was monitored with sticky traps for three seasons (2010 to 2012 inclusive). Emergence started from early October to early November, peaked from late October to mid-November, and was mostly finished by mid-late November. Emergence timing was mainly influenced by year and site, with the largest differences observed between years. Most emergence (90%) took place during an average period of only 19 days each season (range of 11-28 days across all trap types, sites and seasons). The role of temperature in emergence timing was investigated using a degree-day (DD) model. DD accumulated since 1 April using a lower threshold temperature of 15°C and an upper threshold temperature of 35°C or 40°C gave the best predictions of median emergence dates in the three years. The required DDs to achieve 5, 50, and 95% emergence were 336, 403 and 447 DD, respectively. The maximum difference between predicted and observed median dates for 2010-2012 was only four days. CGW adult emergence in future years can be predicted using these DD parameters and a combination of observed and average historical temperature data for the target site. Effective prediction of emergence peaks will allow the timing of pesticide applications to be optimised whilst providing protection for establishing parasitoids which emerge from the galls 2-3 weeks after citrus gall wasp.

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