Nocturnal dispersal flight of crickets: behavioural and physiological responses to cool environmental temperatures

1. Flight of nocturnal insects may be limited by cool nighttime environmental temperatures. We used laboratory and field experiments to explore the thermal basis of nocturnal flight in wing-polymorphic Gryllus lineaticeps crickets consisting of long-winged (LW), flight-capable morphs and short-winged (SW), flight-incapable morphs. These crickets are a model for life history evolution and loss of flight, but their thermal requirements for flight have been unknown. We hypothesized that LW crickets achieve warm body temperatures required for flight through a combination of behavioral thermoregulation, producing heat endogenously (either through initiating muscular thermogenesis or increasing resting metabolic rates), and minimizing heat loss (by circulatory adjustments or insulation).

2. Summer evening air temperatures in the field gradually declined from 25°C to 18°C during the hours of nighttime cricket activity. Laboratory LW crickets did not fly at a body temperature of 18°C, and 60...