Emergence timing and voltinism of phantom midges, <i>Chaoborus</i> spp., in the UK

Abstract

Phantom midges, Chaoborus spp. (Diptera: Chaoboridae), are an important taxon in environmental risk assessment of plant protection products due to the sensitivity of their larvae to insecticides. To aid modelling of population responses to xenobiotic exposure, information on emergence timing and voltinism is needed, but definitive evidence to support these parameters is lacking in the literature. We investigated emergence timing of overwintering Chaoborus larvae and the number of life cycles occurring per year in two separate, mesh-enclosed outdoor microcosm experiments in the spring and summer of 2017. Emergence from overwintering larvae of a population of predominantly C. obscuripes (99.68 %) commenced on 13 April and peaked on 2 May. The majority of emergence was completed by 3 June. Emergence success ranged from 51.4 % to 66.2 %, indicating that for overwintered C. obscuripes larvae, adults emerged contemporaneously in spring, rather than sporadically over the course of spring and summer. A population of C. crystallinus larvae produced up to four discrete generations over the spring and summer months (i.e. were confirmed to be multivoltine), with life cycle durations (egg-to-egg) ranging from 14 to 56 d. The differences in life cycle strategy observed in this study have implications for assessment of the capacity of populations of Chaoborus spp. to recover if there are localised impacts due to insecticide exposure or other stressors.