The contribution of potential beneficial insectary plant species to adult hoverfly (Diptera: Syrphidae) fitness

Providing floral resources in and around crops enhances local hoverfly populations and recent work has identified a number of key flower species as important sources of pollen and nectar for the adult flies. However, the effects of different flower species on hoverfly fitness have never been studied. In the present work, laboratory experiments were conducted to determine the effectiveness of six flowering plant species in enhancing the longevity and several parameters related to fecundity of Episyrphus balteatus (De Geer). Coriander was the most efficient in terms of the proportion of females laying eggs. Buckwheat gave the highest mean longevity, which correlated with the longest egg-laying duration. However, phacelia increased oviposition rate and lifetime fecundity to the greatest extent, and was responsible for the optimal reproductive potential of female E. balteatus. There was no correlation between pollen and nectar consumption or between the quantity of pollen ingested and the resulting female performance. This suggests that recording the presence of pollen in the diet is not an adequate method to evaluate hoverfly preference or pollen nutritional value.If only one floral resource subsidy is being considered for introduction into agricultural and horticultural systems to enhance hoverfly efficacy, phacelia is recommended, at least for E. balteatus.

Highlights► Flowers enhance hoverfly populations in agrosystems for conservation biocontrol. ► Key flower species have been identified as important sources of pollen and nectar. ► We tested the effects of six flowers on hoverfly fitness; it has never been done before. ► Pollen and/or nectar consumption is a poor indicator of female performance. ► We suggest that assessment of flowers for conservation biocontrol has to be improved.