Cotesia congregata is a parasitoid wasp found throughout North America and South America (1). The wasps parasitize caterpillars of sphinx moths, but can also sometimes infect other types of caterpillars (1). A commonly studied host for the wasps is the tobacco hornworm Manduca sexta (1,2).
Eggs deposited into the hemolymph of a caterpillar host hatch into pale yellow-white first instar larvae (2). These larvae grow and molt within the host to become second instar larvae. After further development, the second instar larvae tear through the host cuticle using a saw-like motion of their head to emerge from the host (2). Another molt occurs as the larvae pull themselves out of the host. The discarded parasite cuticle remains within the host to act as a plug to prevent host fluids from leaking out through the hole made by the parasite (2). The now third instar larvae spin a cocoon in which they continue to develop. Within the cocoon, the third instar larvae become pupae, then adults. The adults emerge from the cocoon and fly away to mate. Females that are ready to lay their eggs then search for a new caterpillar host. When they find one they jump on the worm and use their ovipositor to pierce through the cuticle of the host and deposit the eggs into the hemocoel of the new host (2). The host immediately thrashes its head around to drive the wasp away, giving the female only a few seconds to deposit her eggs, usually at the back end of the caterpillar (2).
The wasp larvae have been found to suppress host feeding once they emerge through the host cuticle (3). Likely a consequence of activating the host immune system and wound healing responses, this suppression of feeding also protects the wasps from the host while they’re still in their cocoons (3). At the same time, the parasites partially paralyze the host (4). Once the cocoons are spun the host regains some sensitivity, but has lost self-generated behaviours and is instead left to be a bodyguard to the cocoons by using a defensive strike if threatened by would-be predators of the vulnerable cocoons (4).
1. EENY-598; https://edis.ifas.ufl.edu/publication/IN1042
2. 10.1093/aesa/33.2.231
3. 10.1002/arch.20068
4. 10.1111/1365-2435.14150
Parasite Comics Team:
Dr. Chenhua Li (Lead, Ideas), Dr. Þórey Jónsdóttir (Illustrator, Ideas), Stephen Pollo (Writer, Researcher), Yuanzhe Wang (Digital Consultant).