Synonymy.—Symbius blattarum Sundevall [Leng, 1920].
Natural hosts.—Blattella germanica, on shipboard (Sundevall, 1831); Germany (Aclogue and Fowler, in Burr, 1899a); on steamship "Samui" (Stamm, 1936); on cruiser "Duguay-Trouin" (Barbier, 1947); Hawaii (Williams, 1946a): This last record was based on a specimen dissected from an adult German cockroach collected on an airplane from the South Pacific. The parasite was reported as Ripidius sp. by Williams, but Weber (1948) made the specific identification.
Ectobius pallidus? Abeille de Perrin (1909) stated that R. pectinicornis was first described by Sunders [sic] as blattarum because it had been captured in the body of Ectobia livida. We presume that Abeille de Perrin was referring to Sundevall's work in which the host was given as Blattella germanica.
Periplaneta americana, on shipboard (Sundevall, 1831): One nymph only.
With the exception of the single nymph of P. americana, R. pectinicornis apparently attacks only adult females and nymphs of B. germanica. Barbier (1947) found only B. germanica parasitized, although both Blatta orientalis and Supella supellectilium were prevalent on board the ship. Primary larvae of the parasite failed to parasitize Supella.
Adult behavior.—The winged male is relatively active compared to the apterous female; it runs around, flies well, and jumps on the female when in her vicinity. The female remains stationary and lays eggs around her by bending her long ovipositor (Sundevall, 1831). The eggs (50-100) are laid among a network of silk fibers secreted by the female. The female dies after completing oviposition (Barbier, 1947).
Development.—The eggs hatch after 14 days, and the primary (triungulin) larvae ascend the host's legs to its body; the larvae then cut the intersegmental membrane between the metasternum and first abdominal segment of the cockroach, in order to enter the host's abdomen (Barbier, 1947). Chobaut (1892) first suggested this method of attack by the ripiphorid larva. As the parasites develop, the abdomen of the host becomes swollen. Developing larvae apparently eat the host's fat body, leaving the vital organs until the last. Parasitized female hosts were sterile and the eggs, when formed, never hatched. Development of the oötheca was also inhibited. There were usually two larval parasites per host, but three or four were found several times (Barbier, 1947). Sundevall (1831) found only one larva per cockroach except one host which, when crushed, yielded five. Stamm (1936) found three hosts infested with five larvae each. In a little over 100 cockroaches, Stamm found 10 that were parasitized.
The day before the parasite leaves the host, the cockroach shows an abrupt uneasiness and runs about, finally falling over on its back. The parasite larva emerges from the host through an opening it makes in the membrane between penultimate and last tergite. The host dies a few hours after the larva has left. The larva seeks a sheltered area and pupates within 48 hours. Adults emerge in 9 days (females) and 13 days (males) (Barbier, 1947).
Distribution.—Adult males have been collected in light traps in Hawaii (Van Zwaluenburg, 1946), and the first female was reported by Weber (1948); the parasite is now established in the islands around Pearl Harbor (Dr. F. X. Williams, personal communication, 1953). The U. S. National Museum has specimens of R. pectinicornis from England, Guatemala, Hawaii, Panama, and from Florida and Georgia in the U. S. (Dr. E. A. Chapin, personal communication, 1953). Kono (in Asano, 1937) reported two species in Japan. It is noteworthy that all these records are from localities adjacent to oceans and on ships; none are from interiors of continents. The only biological data were obtained from parasites found on board ships. Sundevall (1831) believed that the parasites boarded his ship with their hosts during loading in Calcutta, since before that not any were seen on board. Barbier (1947) suggested that the parasite must be spread very easily in ports between neighboring ships by parasitized cockroaches in baskets or sacks of provisions.