Droplet bubbling evaporatively cools a blowfly

Abstract

Terrestrial animals often use evaporative cooling to lower body temperature. Evaporation can occur from humid body surfaces or from fluids interfaced to the environment through a number of different mechanisms, such as sweating or panting. In Diptera, some flies move tidally a droplet of fluid out and then back in the buccopharyngeal cavity for a repeated number of cycles before eventually ingesting it. This is referred to as the bubbling behaviour. The droplet fluid consists of a mix of liquids from the ingested food, enzymes from the salivary glands, and antimicrobials, associated to the crop organ system, with evidence pointing to a role in liquid meal dehydration. Herein, we demonstrate that the bubbling behaviour also serves as an effective thermoregulatory mechanism to lower body temperature by means of evaporative cooling. In the blowfly, Chrysomya megacephala, infrared imaging revealed that as the droplet is extruded, evaporation lowers the fluid´s temperature, which, upon its re-ingestion, lowers the blowfly’s body temperature. This effect is most prominent at the cephalic region, less in the thorax, and then in the abdomen. Bubbling frequency increases with ambient temperature, while its cooling efficiency decreases at high air humidities. Heat transfer calculations show that droplet cooling depends on a special heat-exchange dynamic, which result in the exponential activation of the cooling effect.

The upper thermal tolerance for a Texas population of the hairy maggot blow fly Chrysomya rufifacies Macquart (Diptera: Calliphoridae)

“…Another possible explanation for C. rufifacies exhibiting a greater thermal tolerance when provided only water relates to how blow flies evaporatively cool. When adequately hydrated, blow flies engage in a bubbling behaviour where they tidally move a droplet of fluid in and out of their buccopharyngeal cavity (Stoffolano Jr et al, 2008;Gomes et al, 2018), which transfers body heat to the surrounding air and regionally reduces body temperature by as much as 3 ∘ C (Gomes et al, 2018). Furthermore, even if C. rufifacies became dehydrated during this study, they may have used the physical water present in their vial to evaporatively cool via bubbling behaviour, and thus improved their upper thermal tolerance, though further testing is needed to confirm the effectiveness of this behaviour in C. rufifacies.…”

Fly foregut and transmission of microbes

“…Production of these 'bubbles' not only serves as a way of getting rid of the water in the meal by surface evaporation, but for some fly species the adults drop the bubble and later re-ingest it, while for others, bubbling can even serve as a nuptial gift (Aluja et al, 2000;Stoffolano and Haselton, 2013). A recent report (Gomes et al, 2018) suggests that bubbling may also be involved in temperature regulation. I suggest that only in the case where the need to eliminate water from the meal within the crop did this organ become involved with bubbling.…”

Using radiotelemetry to study behavioural thermoregulation in insects under field conditions

“…To accommodate these different requirements, insects have evolved physiological and behavioural adaptations to control their body temperature. A few insect species, including flies (Gomes, Köberle, Zuben, & Andrade, ), bees (Southwick & Heldmaier, ) and moths (Heinrich, ), regulate body temperature physiologically through endothermy or evaporation. However, insects are generally small and characterized by poor insulation and a large relative surface area which results in high rates of heat transfer (Stevenson, ).…”