New Delhi, Oct. 2: When rain or storms loom, insects appear to skip foreplay.
A study by Brazilian and Canadian biologists has shown that insects modify their sexual behaviour under falling atmospheric pressure. Their findings provide what some scientists say could be the first evidence to suggest that insects can anticipate certain changes in the weather.
Entomologist Jose Mauricio Simoes Bento at the University of Sao Paulo and his colleagues have documented reduced courtship sequences in a beetle, a moth, and an aphid under a drop in the atmospheric pressure. High winds or fierce rainstorms are typically preceded by a fall in the atmospheric pressure.
“Insects seem to have evolved mechanisms to detect upcoming bad weather,” Bento, who led the study in Brazil, told The Telegraph in a telephone interview. The scientists have described their findings today in the research journal PLOS One.
The researchers believe the changes they observed in the insects’ sexual behaviour reflect an evolutionary adaptation — a behavioural change that increases the chances of survival during rain or storms that could be severely hazardous for insects.
“A raindrop falling on an insect would be something like a refrigerator falling off a tall building on a human,” said Jeremy McNeil, a team member and associate professor of biology at the University of Western Ontario in Canada who specialises in the reproductive strategies of insects.
The researchers studied the curcurbit beetle, the armyworm moth and the potato aphid under natural changes in the barometric pressure and under pressure changes simulated in a laboratory chamber and detected altered behaviour in all three species.
Under normal atmospheric pressure, the insects displayed standard courtship sequences — the male beetles stroked females with their antennae, while the female moths and aphids “called” males, releasing perfume-like pheromones to draw males.
But under declining barometric pressure conditions, the majority of male beetles mounted females without any intermediate courtship behaviours. And fewer female moths and aphids exhibited calling behaviour under decreasing pressure conditions. The results, the researchers said, suggest the insects skip courtship sequences to avoid getting caught in bad weather.
“We chose three species quite different from each other — the beetle is strong, the aphid is fragile, and the moth is in between,” Bento said. The researchers believe the altered behaviour reduces the probability of injury or death under bad weather.
“If the insects are indeed anticipating changes in weather, this would be an exciting result,” said Kotiganahalli Narayanagowda Ganeshaiah, an evolutionary biologist at the University of Agricultural Sciences, Bangalore, who was not connected with the study.
But Ganeshaiah cautioned that more observations would be required to determine whether the modified sexual behaviour is anticipatory or a physiological response to changing atmospheric pressure.
The study’s results suggest that insects may need to be admitted into the club of select species that have been observed to alter behaviour with barometric pressure.
Earlier this year, wildlife biologists in the US reported what appeared to be white-crowned sparrows sensing and responding with behavioural changes to declining pressure — the lowered pressure stimulated food intake without any change in stress physiology.
Independent research groups in the US and Taiwan have also documented blacktip sharks and sea snakes taking evasive action under falling barometric pressure ahead of tropical cyclones.
The new findings, McNeil said, could also explain earlier observations by entomologists of why insects do not fly under high wind conditions.
The scientists said it was still unclear how insects might exactly be detecting changes in atmospheric pressure. They speculate that insects may be equipped with receptors or sensors that can detect faint air movements or changes in air pressure.
The other members of the team were Ana Pellegrino, Maria Penaflor, and Christiane Nardi in Brazil, and Wayne Bezner-Kerr and Christopher Guglielmo in Canada.