Copidosoma flordanum (looper parasitoid)
Blake Layton (Mississippi State University) and Scott Stewart (University of Tennessee), Department of Entomology and Plant Pathology
This tiny parasitic wasp has no common name. It can be generally referred to as ‘the looper egg-larval parasite’, but in this article we will refer to it simply as Copidosoma. This is one of the more common parasites of loopers, both cabbage loopers and soybean loopers, and it certainly has one of the most interesting life histories of any of the beneficial insects featured in this section. Science fiction writers get a lot of their wilder ideas from reading about parasitic insects such as this one. This parasitoid belongs to the family of wasps known as Encyrtidae. It is listed in the literature both as Copidosoma floridanum and as C. truncatellum.
Copidosoma is referred to as an egg-larval parasite because its eggs are deposited in newly laid looper eggs, but it does not complete its development until the host is in the larval stage. Looper moths deposit eggs individually, usually on the undersides of leaves. Female Copidosoma wasps search for these eggs and deposit either one or two eggs inside each looper egg that they find. Some time after the looper larva emerges and begins feeding the Copidosoma egg begins to divide into additional eggs, 2, 4, 8, 16, 32, etc. Eventually a parasitized looper contains around 1000 of these Copidosoma eggs, all of which may have developed from a single original egg and all of which are genetically identical. Thus, if only one Copidosoma egg was initially placed in the looper egg, all of the Copidosoma eggs will be either male or female. When two Copidosoma eggs are initially placed in the same looper egg, they are usually of opposite sexes.
Once the parasitized looper larvae reaches its fifth larval instar, changes in the growth hormones of the looper trigger the Copidosoma eggs to hatch and begin feeding within the body of the host caterpillar. Strangely, this also stimulates the host larva to delay its pupation and have additional larval instars, resulting in a larger larva that provides more food resources for the parasites developing within its body. The looper larva remains alive until after it forms its pupal cocoon on the underside of a leaf, but then dies, due to the feeding of the Copidosoma larvae, before it has a chance to pupate. By this time the body of the looper caterpillar is completely filled with the bodies of the Copidosoma parasites, which by this time have also pupated. The resulting looper mummies are initially tan to gray in color and have a grainy appearance due to the presence of the large number of Copidosoma pupae that can be seen through the “skin” of the looper. If one collects one of these mummified loopers and places it in an enclosed container, it will “hatch” within a few days into hundreds of very small, gnat-like adult Copidosoma. In one Louisiana study the average number of Copidosoma to develop from parasitized soybean loopers was 992, but as many as 2500 to 3000 parasites have been recorded from individual larva.
As mentioned previously, Copidosoma attacks both cabbage loopers and soybean loopers, and it also attacks other loopers as well. In a report from Louisiana, approximately 9% of all soybean loopers collected were parasitized by this wasp. However, levels of parasitism are often considerably higher than this during the latter part of the season. Because parasitized loopers are killed before they emerge as moths and have a chance to reproduce, Copidosoma does help reduce overall looper populations. But this is one parasite that can actually contribute to increased levels of crop injury. Because parasitized loopers often have additional larval instars and grow larger, they actually eat more than they would if they were not parasitized. In another Louisiana study, parasitized soybean loopers weighed 50% more and consumed 40% more leaf area than non-parasitized larvae.