Little is known of the effects of predatism and parasitism on natural populations of cockroaches. Many statements in the literature are very general; yet there are a few data on egg parasites (e.g., Tetrastichus hagenowii) which suggest that, in the absence of parasites, populations of domestic cockroaches might be much larger than they are in certain areas. We have summarized the literature on natural control and also that on the use by man of predators and parasites in the biological control of cockroaches. However, because of the paucity of information, we have been unable to evaluate the effectiveness of biological control in reducing the numbers of pest cockroaches. This is an area that might reward further investigation.
INVERTEBRATES
Scorpions.—In Puerto Rico, cockroaches are probably the principal food of the scorpions which live in old houses, on tree trunks, etc. (Seín, 1923). The staple diet of scorpions in Arizona is the small cockroach commonly known as the water bug (Stahnke, 1949); in the part of Arizona where he resides, Stahnke (personal communication, 1953) says that the "water-bug" is most generally Supella supellectilium although Blattella germanica is also found, but less abundantly.
Spiders.—Jefferys (1760) mentioned a large spider which was protected in the Antilles and especially on Guadeloupe because it hunted down and fed on cockroaches; the spider was reputed to be common in every house. Sir Hans Sloane (1725, in Cowan, 1865) reported that residents of Jamaica kept spiders in their houses to destroy cockroaches. Takahashi (1924) reported that, in the Taihoku area of Formosa, human habitations contained large numbers of spiders which caught and ate cockroaches. Smith (in Marlatt, 1915) reported that Brazilians encourage large house spiders because they tend to rid the house of "other insect pests." In British Guiana tarantulas were kept in a bungalow to control Periplaneta and Pycnoscelus (Beebe, 1925a).
Ants.—A Madam Merian noticed that ants cleared houses of cockroaches (Kirby and Spence, 1822). A small reddish-yellow ant, called Pucchuçiçi by Peruvian Indians, pursued and destroyed a cockroach called Chilicabra which was a pest in native huts (Tschudi, 1847). Schwabe (1950b) found swarms of ants attacking living Pycnoscelus surinamensis and stated that ants are probably the chief enemy of this cockroach in Hawaii. Wallace (1891) stated that in Africa a band of driver ants may enter a house and clear it of cockroaches and other arthropods. In British Guiana, Beebe, (1925) found that several times a year army ants cleared the laboratory of all cockroaches and tarantulas.
Wasp egg parasites.—Matsumura (1917, in Asano, 1937) proposed that parasitic wasps such as Evania and Brachygaster be protected in Japan as the natural enemies of cockroaches. In one area in France, 20 percent of the oöthecae of Loboptera decipiens were parasitized by Zeuxevania splendidula (Genieys, 1924). Edmunds (1952a) found that 12 percent of 459 oöthecae of Parcoblatta collected during December through April of 1950-51 in Ohio were parasitized; evaniids accounted for about 7 percent of the parasitization. Additional collection data in 1951-52 Edmunds (1953a) showed that 8.7 percent of 320 wood-cockroach oöthecae were parasitized; 2.8 percent of these parasites were evaniids; almost 13 percent of the egg capsules collected showed evidence of previous parasite emergence. Cameron (1957) reported that oöthecae of Periplaneta americana collected in Saudi Arabia were 29 percent parasitized in March and 25 percent parasitized in October by Evania appendigaster. Sonan (1924) found 1 of 65 oöthecae of P. americana and P. australasiae parasitized by E. appendigaster in Formosa.
Cottam (1922) stated that the increase of Supella supellectilium in Khartoum was checked by a wasp egg-parasite that was later identified as Anastatus tenuipes (see p. [246]) (Ferrière, 1930, 1935). In this country, this wasp seemed to be effective in decreasing the numbers of Supella in certain areas in Arizona (Flock, 1941).
In Formosa, Tetrastichus hagenowii was an important parasite of cockroach eggs (Maki, 1937). Sonan (1924) reported 30 percent parasitization of 65 oöthecae of Periplaneta americana and P. australasiae collected in Formosa. In Bangalore, India, the natural parasitization of randomly collected oöthecae of P. americana varied from 21 percent (of 495 oöthecae), July 1947-June 1948, and 43 percent (of 288 oöthecae), July-December 1948, to 57 percent (of 178 oöthecae), July-October 1949 (Usman, 1949). Cameron (1955) obtained T. hagenowii from oöthecae collected in Trinidad, B.W.I., and Saudi Arabia; some 15 percent of the oöthecae of P. americana and P. australasiae collected in October in Trinidad were parasitized; a later collection (March) was 34 percent parasitized; a small sample of P. americana oöthecae was 65 percent parasitized. The oöthecae collected in Saudi Arabia in March were 20 percent parasitized. Plank (1947) found that the eggs of the American cockroach in Puerto Rico (probably in laboratory cultures) were so heavily parasitized by T. hagenowii that he had to use P. australasiae for experimental purposes; in 1950 Plank stated that more than 50 percent of American cockroach oöthecae were parasitized.
Fahringer (1922) stated that Prosevania punctata could be used to eradicate cockroaches, but he did not test his hypothesis. Marlatt (1902) felt that the usefulness of Evania appendigaster in biological control was impaired by Tetrastichus acting as a hyperparasite (see footnote 6, p. [236]). However, Wolcott (1951) stated that in Puerto Rico E. appendigaster is quite abundant and is a factor of considerable importance in controlling cockroaches. Kadocsa (1921) stated that Brachygaster minutus and Evania appendigaster were not important in the biological control of cockroaches. These general statements are not supported by experimental evidence.