Since remote times humans have been interested in the weather and have used different strategies to predict bad storms. Some of these strategies rely on the observation that in anticipation of storms, birds fly at low heights and cows lie down. Some people even claim to feel their bones ache. These and other similar accounts have been reported but not scientifically tested.
In a paper entitled Weather Forecasting by Insects: Modified Sexual Behaviour in Response to Atmospheric Pressure Changes, the group of Dr José Maurício Simões Bento at University of São Paulo (College of Agriculture "Luiz de Queiroz") teamed up with Dr Jeremy N. McNeil and Dr Christopher G. Guglielmo at University of Western Ontario to show for the first time that insects modify their mating behavior in response to a drop in air pressure, which in most cases is a sign of imminent rain.
The experimental study included three different species of insects belonging to very distinct orders and compared their mating behaviors under falling, stable, and increasing air pressure conditions. With a Y-tube olfactometer, which is an instrument used to assess insect responsiveness toward odors, the group exposed males of curcurbit beetle (Diabrotica speciosa) to female pheromone extracts and observed that under falling air pressure males showed less motion and interest in females than in either stable or increasing atmospheric pressure. The group also observed that when in contact with females, males did not put too much effort into courtship and mating occurred faster under dropping atmospheric pressure, a behavior that might be explained by a sense of imminent death. For Dr Maurício Bento, loss of interest in mating during the hours before the storm is an adaptation that "reduces the probability of injury and death of insects, which makes sense if you consider that high winds and rainstorms are life-threatening for them."
The number of times that true armyworm moth (Pseudaletia unipuncta) and potato aphid (Macrosiphum euphorbiae) females exhibited calling behavior, which is the way females of these species attract males for copulation, was also tested under different atmospheric conditions and the observation was similar: calling behavior, and thus mating, was significantly affected by changes in air pressure.
The fact that all three species analyzed modified their mating behavior in response to changes in air pressure suggests that all insects are adapted to respond to potential bad weather. As a number of vertebrates feed on insects, it is possible that animals' foraging activity is also disrupted in response to decreasing air pressure. Thus, the effects of barometric pressure might also impact ecological communities as a whole. The group now plans to examine the mechanisms associated with this adaptive behavior.
The paper has been published in PLOS ONE and is available at http://dx.
Funding information: INCT Semioquímicos na Agricultura (FAPESP, CNPq), NSERC, CFI, and the Ontario Research Fund