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Environmentally cued hatching in the bird-parasitic nest fly Philornis downsi

Abstract:

Under the hypothesis of environmentally cued hatching (ECH), eggs are stimulated to hatch by cues favouring larval survival. Here we investigated whether the bird-parasitic nest fly Philornis downsi Dodge & Aitken (Diptera: Muscidae) exhibits ECH in response to the presence of suitable hosts and environmental conditions. Philornis downsi is an invasive in the Galapagos Islands and ECH could help to explain its success in a novel habitat. We found that the presence of hosts (nesting birds) per se does not accelerate hatching time in P. downsi, but that nesting birds do produce a microclimate, in terms of temperature and/or humidity that is conducive to faster hatching and higher hatching success. Eggs that are laid under extremely dry conditions die rather than delay their hatching time. We also found that P. downsi eggs hatch more rapidly when the substrate is very wet. Furthermore, larvae that hatch rapidly survive longer under starvation conditions. We suggest that eggs hatching more rapidly can either take advantage of optimal conditions for larval growth (host presence) or escape unfavourable microclimatic conditions (as larvae are mobile).