Studies on gall-inducing behaviour and life cycle to aid host specificity testing of Notomma mutilum (Diptera: Tephritidae) – a prospective biological control agent for prickly acacia (Vachellia nilotica subsp. indica)

Abstract

The gall-inducing tephritid fly Notomma mutilum (Bezzi) (Diptera: Tephritidae) from Senegal is a prospective biological control agent of prickly acacia, Vachellia nilotica subsp. indica (Benth.) Kyal. & Boatwr (Fabaceae) in Australia. Wide variation in the oviposition behaviour and life cycle of N. mutilum in quarantine resulted in difficulties with colony maintenance and host specificity testing. To identify the factors responsible, adults that emerged from galls cut from plants 100 days after oviposition (enforced population, EP) were compared with adults that emerged from galls on the plants (normal population, NP). Oviposition by females of different ages did not vary significantly. The EP females had more variable egg-laying (galls on 46.8% plants) and made fewer oviposition scars (≈37 per female) than NP females (galls on >90% plants and ≈95 scars per female). However, the life cycle duration of EP progeny was shorter (140.7?±?1.7 days) and less variable than NP progeny (160.1?±?12.8 days). Egg-laying on all the plants was achieved when a greater number of EP adults (three pairs) were used. Actively growing tender shoots in the upper crown of the older host plants were preferred sites for oviposition. Galls were initiated (3.5?±?0.2 days) before egg hatching (11.3?±?0.3 days), and bigger (longer and wider) galls were observed on the preferred oviposition sites. Therefore, plants with actively growing shoots in the upper crown should be selected for host specificity testing and three pairs of N. mutilum adults should be used.