Sunday, June 24, 2007

Cockroach parental care: the story continues

One of the nice things about posting online is the reach and the variety of people who see your stuff and how they in return contribute to your knowledge. I recently received an email from George Beccaloni from the NHM who works on cockroaches who stumbled upon the parental care in cockroaches picture.

It turns out that someone has actually looked at this behavior carefully before. The work was ironically published in a journal whose offices are a short walk from here, Current Science. Here's what Dr. Beccaloni wrote to me.

"Your photo is of a female cockroach in the genus Thorax or Phoraspis. The amazing thing is that the nymphs feed on the blood of the mother which they obtain by biting small holes in the membranes between the segments of her abdomen. Here is some information taken from this book:

"Phlebonotus pallens Serville, a semi-aquatic species found in India, clearly falls in the latter category. Pruthi (1933) collected a female in south India, not noticing anything extraordinary about the specimen. Upon sorting his catch, however, he found that the roach had about a dozen nymphs under her wings. "The wing covers are opaque and the young ones lying under them are so nicely packed," her commented, "that the human eye cannot easily detect on superficial examination that the individual is carrying so many young ones on its body."
Females of this species are flightless, with the hindwings greatly reduced. The forewings, however, are fully formed and arched to create the nymphal space beneath.
Roth (1981) speculated that the arched tegmina found in the related genera Phoraspis and Thorax might suggest similar maternal care in those roaches.
He was proved right: Indian entomologist S. Bhoopathy reported in 1998 that the first two nymphal instars of the epilamprine Thorax porcellana Saussure are carried snugly beneath the domed forewings of their mother. This cryptic species feeds on clumps of dead vegetation trapped by the densely intertwining branches of certain shrubs (e.g., Prosopis spicigera, Gymnosporia montana, and Flacourtia sp.). Females produce a single clutch of about 40 eggs annually.
Bhoopathy's 1998 study provides the only detailed observation of actual migration of neonate cockroaches to the dorsal depression under the wings (the cockpit?), and so is worth quoting: "Immediately after hatching, the first instar nymphs...crawled over the abdomen of the mother. The upper surface of her abdomen became markedly depressed into a fairly tight spacious trough or chamber with its sides raised. As the nymphs crawled over her body, she raised up her tegmina, which were large, tough, and dome-shaped, and all the nymphs were accommodated compactly; the tegmina were placed in position so as to conceal all the nymphs and to afford perfect protection." It is further noted that the concave dorsal "trough" in which the nymphs ride essentially forms upon the birth of the nymphs, by retraction of the distended internal brood sac after they vacate (Bhoopathy 1998).
More remarkable still, T. porcellana nymphs were found by Bhoopathy to derive liquid nourishment from specialized dorsal pores in their mother's dorsum as well as by the macabre means of piercing her cuticle with specialized sharp mandibles! The nymphs have relatively long, sharp mandibular tooth-like processes, present only in the first two instars, which penetrate the female's abdominal intersegmental membrane. Hemolymph or some other fluid oozing from the wounds is then imbibed by the young roaches. T. porcellana's specialized neonate feeding adaptations - a larger head relative to the body in the first two instars, and mandibular "teeth" lost in later instars - are not as extreme as those of some roaches (see Perisphaeriinae below), but this trophic interaction is curious indeed. Bhoopathy showed that this is an obligate mode of feeding for neonates, as they soon die if removed from the mother. It is hard to say if some other factor contributed to their decline. I would think, for example, that the neonates would be especially prone to desiccation if removed from the cozy chamber atop the mother. Still, the morphological modifications of both mother and offspring indicate the closeness of their relationship; do the dorsal pores provide "milk" of sorts to the young? And is the milk supplemented by blood (hemolymph)?" "


Anonymous said...

Ewwww....kill them all.
Sick, sick, sick things.

Natasha said...

Eh, hardly...

Scythemantis said...

"kill them all?" They're absolutely gorgeous, fascinating, wonderful animals. Very few members of the roach group are pests, and even the pest species are clean and harmless. These blood-drinking baby roaches are especially amazing and awesome. The only sick thing here is your lack of respect for nature's perfection...I hope a thousand roaches smother you in your sleep, anonymous jerk :p

Natasha said...

Have you heard of Archie and Mehitabel? You should look up Don Marquis in general you might enjoy him.


Buggy said...

Thats very interesting,Gromphadorhina Portentosa newborns stay on,under,and around their mother for a day or so before leaving and starting a new life.I cant imagine the nymphs drinking mamas blood!