Wednesday, June 13, 2018

Post #22
Donald A. Windsor

The Strepsiptera is an order of parasitic insects containing about 600 species in 9 families, 3 extinct and 6 extant (1). Bizarre is a good way to describe them because they do not seem to fit in prevailing phylogenetic schemes.

Caenocholax fenyesi is a species in the order Strepsiptera, family Myrmecolacidae. Its males parasitize ants and its females parasitize crickets (2).

Three ant species host male C. fenyesi: Dolichoderus bispinosus, Red Fire Ant Solenopsis invicta, and Camponotus planatus (Order Hymenoptera, Family Formicidae). Two other possible host species were not named.

The cricket species hosting female C. fenyesi is Macroanaxipha mecilenta (Order Orthoptera, Family Gryllidae).

The first-instar larvae are not sexually dimorphic and, apparently, sex is determined by the host species. If a larva enters an ant it becomes a male; if it enters a cricket, it becomes a female. Males undergo a complete metamorphosis from larvae to flying adults. Females go from larvae to a neotenic adulthood (no wings). Males leave their host ants after pupation and live for only a few hours; they do not eat. Females spend their entire lives in their cricket hosts, only poking out their genitalia to receive sperm from the male, who copulates on the abdomen of the hosting cricket. Males find female genitalia by following pheromones exuded by the females. The resulting larvae feed on their mother until they emerge and manage to find and enter a host.

This life cycle is so fraught with disaster that it is a wonder it works. The research described by Kathirithamby in several articles is daunting and frustrating but will probably turn up even more amazing situations.

Strepsipteran parasites seem to have plenty of opportunities to acquire multiple species of hosts and more should be discovered as interest in this order increases. Meanwhile, I wonder if this separation of host species for males and females occurs anywhere else besides in the Myrmecolacidae.

References cited:

1. Strepsiptera. Wikipedia.

2. Kathirithamby, Jeyaraney ; Johnston, J. Spencer. The discovery after 94 years of the elusive female of a myrmecolacid (Strepsiptera), and the cryptic species of Caenocholax fenyesi Pierce sunsu lato. Proceedings of the Royal Society of London B (Supplement) 2004; 271: S5-S8.


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