When Xenos peckii twisted-wing parasite males emerge as adults from within the body of the hapless wasp that served as their incubator, the race is on. With an adult lifetime spanning just a few hours, the male insects have to locate a female and mate before their time is up. And the challenge of locating a female mate – which is barely more than a fleshy bag of eggs with no eyes or limbs – is particularly problematic. Concealed within the body of her own host, only the female's head and mating channel protrude from the surface.

Despite their short lives and single-minded mission, the males are equipped with extraordinarily sophisticated hybrid eyes – composed of up to 50 micro-eyes, each equipped with a lens that projects a minute image onto a mini-retina of ∼100 photoreceptors. However, it was unclear whether these extraordinary creatures have colour vision. According to Elke Buschbeck, from the University of Cincinnati, USA, some evidence suggested that the nocturnal males may lack colour vision, but with the jury still out, Buschbeck and her colleagues Marisano James, Sri Nandamuri and Aaron Stahl embarked on a study to discover whether the insects’ extraordinary eyes include the basic equipment for colour vision.

Having stumbled across a fertilized X. peckii female during the summer and nurtured the offspring in northern paper wasps until the adult males emerged, Buschbeck and her team had only 3 h to investigate the males’ eyes before they perished. Cooling the insects to extend their life expectancy, Nandamuri and James then measured the electrical signals produced by the eyes in response to flashes of light ranging from ultraviolet to red wavelengths. Meanwhile, Aaron Stahl analysed the insect's gene expression pattern to identify which light-sensitive opsin proteins – which are essential for colour vision – are produced by the insects.

Impressively, the males’ responses were strongest to green light (around 539 nm), while they responded more weakly to UV light (around 346 nm). And when the team analysed the results of Stahl's gene expression investigation, they identified one expressed gene that could produce a green-sensitive opsin, in addition to another that could produce a UV-sensitive opsin.

Although the team emphasises that these observations are not categorical proof that twisted-wing parasite (strepsipteran) males have colour vision, they say, ‘the presence of distinct UV and green opsins presents the possibility that UV-green coloration could play a significant role in strepsipteran ecology, such as helping the male to find the female’. And they wonder whether our own limited colour vision means that we are missing one of the parasite's key tricks: could the females be advertising their presence in their cryptic hideaways by reflecting UV light – like bright homing beacons – to attract the males during their final desperate search? ‘If so, this could help explain another aspect of the complex life cycle of these extraordinary insects’, says Buschbeck.

S. P.
E. K.
The unusual eyes of Xenos peckii (Strepsiptera: Xenidae) have green- and UV-sensitive photoreceptors
J. Exp. Biol.