"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

March 26, 2015

Emblemasoma erro

During summer the air is filled with the rattling ruckus of cicada songs. Male cicadas produce this summer choir using a pair of noise-making organs located in their abdomen, with the aim of getting attention from any prospective mates. But in some cases, they can also end up with some unwanted attention.

Top: Male Tibicen dorsatus cicada
Bottom: Female Embelmasoma erro fly
Photos from Figure 1 & 2 of this paper
The species we are featuring today is an "acoustically hunting" parasitoid fly - it eavesdrops on the male cicada's flirtatious serenading and uses it to home in on its target. This fly is commonly found on the Great Plains of North America and is a scourge to male cicadas, especially male Tibicen dorsatus.

Most of what is known about such acoustically hunting parasitoids are based on flies from the Tachinidae family - one of which targets crickets (I talked about how crickets on Hawaii evolved to become silent due to the presence of one such parasitoid fly here). But this fly belongs to a different family (Sarcophagidae). Only one species of Emblemasoma is well-studied - E. auditrix- and even though Emblemasoma is widely use in the study of insect hearing, not much is known about how they actually live out in the wild. Until now, the only information available on E. erro are based on two scientific papers - one published in 1981 and the other published in 2009. The paper we are featuring today provides some much-needed update on key aspects of this parasitoid's ecology and life history.

This paper reports on a series of field surveys and laboratory experiments that documented the parasitoid's occurrence, abundance, behaviour, and developmental cycle.

The field surveys were conducted at study sites located across Kansas and Colorado. The surveys found that a bit over a quarter of male cicadas were infected with E. erro larvae, and because of how the flies track down their host, almost all the infected cicadas were male - except for one very unlucky female cicada, which most probably got infected because she was responding to the call of a male, ran into a larvae-ladened E. erro that had the same idea, the latter decided that any cicada will do. Talk about a case of fatal attraction!

And it is indeed the sound of the male cicada's serenade that draws in those flies - a loudspeaker playing the recordings of cicada calls is sufficient to attract the attention of E. erro, but a female fly need more than that to commit to dropping off her precious offspring. In outdoor cage experiments where flies and cicadas were housed together and allowed to mingle freely, the researcher observed that even if an E. erro finds herself perched next to a cicada, she will only attack when the host makes any sudden movements. So E. erro uses two separate signals to track down its prey; an acoustic signal at long range in the form of the cicada's call to guide them in, and a visual signal at close range in the form of cicada movement to confirm the host's identity

Emblemasoma erro larva emerging from a cicada
From Figure 6 of this paper
Once she has confirmed her target, the female fly makes an attack run, and very quickly drops off between 1-6 maggots (usually 3) on the base of the cicada's wings. As soon as the maggots land, they immediately start burrowing between the segments and into the cicada's body. The maggots then start devouring its host alive from the inside. Depending on the temperature and clutch size, they take about 88 hours to reach a large enough size to start pupating. At the end of this period, the maggots use teeth-like "oral hooks" to chew their way to freedom, fall onto the soil below to become pupae, and leaving the cicada an empty husk.

So while the aim of the male cicada's singing is to attract the attention of female cicadas, some of them may instead end up getting attention from females of a very different species, and become reluctant incubators for the broods of some keen-eared, cicada-hunting flies.

Stucky, B. J. (2015). Infection behavior, life history, and host parasitism rates of Emblemasoma erro (Diptera: Sarcophagidae), an acoustically hunting parasitoid of the cicada Tibicen dorsatus (Hemiptera: Cicadidae). Zoological Studies, 54: 30.

No comments:

Post a Comment