Data for: Oviposition fluids mediate larval competition

Parasitoid wasp larvae engage in intense interspecific competition when
sharing a host insect, with lethal consequences for the losers. Larval
parasitoid competition is generally thought to be resolved by physical
traits, such as enlarged mandibles. Although solitary parasitoid larvae
are typically superior competitors against gregarious larvae, such
physical traits are unlikely to be effective against large numbers of
competitors. Larval competition may instead be mediated by maternal
factors that increase the survival of offspring facing interspecific
competition, thus increasing parental fitness. When laying eggs inside a
host, many female parasitoids also inject oviposition fluids that are
known to suppress host immune responses, permitting successful offspring
development. We explored whether the oviposition fluids of two wasp
species in the genus Cotesia (Cotesia rubecula, a strong
competitor that almost always wins interspecific competition against a
weaker competitor, Cotesia glomerata) might also represent
maternal factors that improve the interspecific competitive ability of
their offspring. We demonstrate that injections of both venom and calyx
fluid from C. rubecula can inhibit egg hatching and larval
development of C. glomerata. Venom from C.
rubecula decreased C. glomerata egg development
by 2.7 times, and calyx fluid injections caused deformities in 23% of
developing C. glomerata. In contrast, reciprocal
injections of the oviposition fluids from C.
glomerata did not inhibit the development of C.
rubecula. Our results show that maternal factors can improve the
interspecific competitive ability of parasitoid larvae, challenging the
previous assumptions that larval competition was resolved primarily
through physical combat or larval secretions.