The cockroaches are nearly all female, but that hasn’t stopped them spreading to many parts of the world. Would you be able to ID a Surinam cockroach?
Common name: Surinam or greenhouse cockroach
As with most pest cockroach species, the name has little connection to where the species actually originated. They were originally native to Indomalaya, but first described from Suriname in South America.
Scientific name(s): Pycnoscelus surinamensis (Family Blaberidae, Order Blattodea)
Description: Adult Surinam cockroaches are between 18 to 25mm in length. Their bodies are dark brown, or black, and glossy on most parts of the body. The rear sections of the abdomen have a rough, dull surface, which distinguishes them from the similar oriental cockroach Blatta orientalis which is glossy on all segments.Adults may be winged or entire wingless. The extremely rare males have longer wings, but neither sex are strong fliers. The wings may be brown or olive brown. In winged adults, the pronotum (head shield) is diamond-shaped, and slightly wider than the wings, with a pale band around parts of the edge. The cerci – sensory organs at the tip of the abdomen – are small and mostly concealed.
Pycnoscelus surinamensis is unusual in that it reproduces by entirely by parthenogenesis – embryos develop from unfertilized eggs. They actually reproduce by thelkytokous parthenogenesis which results in offspring which are nearly all female. In some populations, males are entirely unknown. Eggs hatch internally, with 30 to 36 young born alive. The remains of the ootheca are expelled from the body after hatching and are readily eaten by the newly hatched nymphs.
Geographic distribution: Now found in tropical and subtropical areas worldwide, including all warmer Australian cities, but is also a recent arrival in Perth, WA. The parent species P. indicus remains endemic to Indomalaya, but is also established in Hawaii and Mauritius. P. indicus is anatomically very similar to P. surinamensis, but still reproduces sexually.Habitat: Surinam cockroaches are a burrowing species, and require moist soil to thrive. Well-mulched gardens, or moist potting mix, are ideal, but they will also refuge in wood piles, under bark, and underneath pavers. Most houses are too dry to suit them, but infestations in houses and offices can be linked to potted plants.
Pest status: Pycnoscelus surinamensis is considered peridomestic – thriving in the gardens provided by humans. When they emerge to feed at night, they can heavily damage plant shoots, making them a particular problem in greenhouses which can support large populations. They are also a known host of parasitic roundworms that infect the eyes of poultry.
Treatment: Because the Surinam cockroach is most often found outdoors, suitable insecticides should be applied to wood piles, mulch, greenhouses, and other infested locations. Residual insecticides applied as barriers around houses can substantially reduce populations as well. Infested potted plants inside buildings or offices may be treated with sprays or granules.
Daniel Heald, technician and entomologist