When a blood-sucking Rhodnius prolixus bug settles down to lunch,it is often at risk of being thwacked by its prey; no one likes being dined upon. Given the risks that a hungry insect runs when filling up,Aurélie Bodin and her colleagues Clément Vinauger and Claudio Lazzari wondered whether fully fed bugs ignored tempting cues sent by their food in a bid to prolong life(p. 2386).
Knowing that hungry bugs respond to vital signs, such as exhaled CO2 and warmth, the trio tested hungry and well fed bugs' responses to a jet of CO2 and warmth. All of the insects responded enthusiastically to the jet of CO2 by approaching it before dining,but as soon as they had eaten, their behaviours changed. The males failed to respond to the CO2 jet, wandering in all directions, and at first the females and larvae were equally unresponsive to the CO2. However, several days after sucking blood, both the larvae and females began backing away from the CO2 jet; instead of attracting them, the gas was repelling them. Eventually, after almost 3 weeks and another period of disinterest in the gas jet, the insects rediscovered their taste for CO2, and started heading towards it again, presumably in the hope of catching another blood meal.
Curious to find out how the bugs' motivation changes after a meal, the team tested how the bugs responded to signs of life after feeding on saline solution that distended the insects' abdomens but didn't provide nutrition. The insects were no longer attracted to the CO2, but females and larvae were no longer actively repelled by the gas either, suggesting that there was something in the blood meal that turned the females and larvae off hunting for hosts.
The team also tested injected starved bugs with haemolymph taken from newly fed bugs and successfully turned off the starved bugs' attraction to CO2 and warmth, making Bodin and her colleagues suspect that whatever reduces the well fed insect's attraction to CO2 is carried in the haemolymph.
So Rhodnius bugs are turned off searching for signs of life after a blood meal, presumably to reduce their risk of being squashed to death by their dinners.