Biology of the Gall Midge Spanolepis selloanae (Diptera, Cecidomyiidae), a Candidate Biological Control Agent of the Invasive Grass Cortaderia selloana

ABSTRACT

Diptera represent an emerging group of potential biological control agents for management of invasive alien species. Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. (pampas grass), a prominent global invader, is commonly managed through mechanical and/or chemical control, but the efficacy of such methods is limited. Here we provide updated information on the biology, ecology and potential use of the gall midge Spanolepis selloanae Gagné, 2021 (Diptera, Cecidomyiidae, Dasineurini), a candidate for the biological control of C. selloana . This midge was recently introduced, most likely from the native area of C. selloana , and has spread rapidly across the Iberian Peninsula. It infests C. selloana by laying eggs and growing larvae in the inflorescences, synchronized with flowering time of the plant, resulting in a multivoltine life cycle. Infestation probability decreases from the basal to the apical sections of both inflorescences and spikelets, with a mean prevalence of infestation per plant over 60% of the total florets. The ratio of fertile to infested florets decreased as the flowering season progressed. Infestation sharply reduced seed output, and larval‐damaged caryopses showed significantly lower germination capacity. The high prevalence of the midge and its combined reduction in caryopsis production, condition, and viability causes a very strong reduction in the overall reproductive output of C. selloana . We did not observe traces of infestation in any other grass species, suggesting a complete specificity of the host plant. Larvae of S. selloanae can be successfully preserved in cold conditions, but larvae collected early in the season showed high mortality under storage conditions. These results provide a robust basis for the evaluation of S. selloanae as a potential biological control agent for C. selloana .