A sexy way of weather forecasting

Some study computer models. Other folks claim they can predict weather changes by whether their bones ache. Still others say birds fly low and cows lie down when stormy weather looms.

But scientists say there’s a sexier way to tell if it’s going to rain: watch the mating behaviour of insects.

A group of scientists from the University of Sao Paulo (College of Agriculture “Luiz de Queiroz”) teamed up with researchers at the University of Western Ontario to show for the first time that insects modify their mating behaviour 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 behaviours under falling, stable, and increasing air pressure conditions.

With a Y-tube olfactometer, which is an instrument used to assess insect responsiveness toward odours, 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.

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 army worm moth (Pseudaletia unipuncta) and potato aphid (Macrosiphum euphorbiae) females exhibited calling behaviour, which is the way females of these species attract males for copulation, was also tested under different atmospheric conditions. Calling behaviour, and thus mating, was significantly affected by changes in air pressure.

The fact that all three species analyzed modified their mating behaviour 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.

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