Can the ladybird predator Scymnus nubilus contribute to control of the aphid Aphis frangulae, a pest threatening the Macaronesia endemic Frangula azorica?

Aphis frangulae (Hemiptera: Aphididae) is a major pest of the laurel forest endemic Frangula azorica (Rosales: Rhamnaceae) produced in nursery conditions by the Forestry Services of the Azores (Portugal). The suitability of A. frangulae for the development and reproduction of a potential biological control agent, Scymnus nubilus (Coleoptera: Coccinellidae), was assessed under laboratory conditions (25 ± 1 °C, 75 ± 5% RH, 16:8 L:D photoperiod). The predation potential of S. nubilus was also assessed. Scymnus nubilus 4th instar larvae and pupae successfully completed development in 9.0 ± 0.2 days. The 4th instar larvae ate 15.1 aphids per day, corresponding to 1.52 mg of biomass ingested. On A. frangulae, S. nubilus females took 5.5 ± 0.3 days to start oviposition and an average of 135 ± 12 eggs were laid per female over the first 15 days of oviposition. Field tests showed that S. nubilus 4th instar larvae were more efficient in controlling the pest in closed systems (isolated aphid colonies) and the effect was more pronounced at high predator densities within three days. In open systems, the aphid natural control was higher than initially expected. This work highlights the role of the large aphidophagous guild present in forestry nurseries. The results of this study show that A. frangulae is an essential prey species for S. nubilus and therefore the predator can be used in pest management programs against this pest. However, further studies focusing on different biological control tactics (inundative or inoculative) are required to assess more accurately the effectiveness of S. nubilus as a biological control agent against A. frangulae.