Soil moisture reduces egg mortality during wildfires in the Madeiran green bush-cricket.

The increasing frequency of fires is a major threat to biodiversity around the world, further facilitated by global warming. Fires usually affect insect populations directly, but insect eggs may partly be protected from wildfires when oviposited into the ground. Madeira belongs to the Macaronesian islands which experience wildfires annually. The Madeiran Green Bush-Cricket (Psalmatophanes barretoi) is endemic to the island and listed on the IUCN Red List as Vulnerable with wildfires being named as the major threat to the species. However, it remains unclear whether the eggs of P. barretoi may be partly protected from fires due to the oviposition substrate (soil). It also remains unknown whether increased temperature alone or increased drought are more important drivers of mortality when fires are approaching or surpassing an oviposition site. We hypothesized that drought might have a significant effect on mortality when heat levels remain slightly below or above mortal temperatures. Therefore, we tested the effects of temperature and drought on egg survival in two laboratory experiments by incubating eggs at different temperatures (49 °C, 55 °C) for six hours with and without water replacement. Our results show that the combination of drought and heat affected egg mortality significantly stronger than heat alone. As a result, we conclude that egg mortality is strongly mediated by soil desiccation and that eggs might be buffered from fire effects in moist habitats or after increased rainfall. Implications for insect conservation: Our results suggest that soil moisture is a key variable to mitigate egg mortality from wildfires. This can be reached by protecting habitats with high soil moisture (e.g. laurel forests and many native bushes) or by prescribed burning during the winter months when soil moisture is higher than in summer. [ABSTRACT FROM AUTHOR]