Up and to the light: intra- and interspecific variability of photo- and geo-tactic oviposition preferences in genus Trichogramma

Trichogramma are parasitic microwasps much used as biological control agents. The genusis known to harbor tremendous diversity, at both inter- and intra-specific levels. The successful selection of Trichogramma strains for biocontrol depends on characterizing the existing diversity in this group, especially regarding oviposition performance and behavior.Oviposition preferences in relation to environmental cues such as light and gravity havereceived little attention so far, although they are suspected to play an important role inmicrohabitat selection and parasitism patterns. The extent of their variability, and theirpotential correlated variations, is virtually unknown. Here we use a novel experimental approach relying on automatic image analysis to characterize the oviposition preferences inrelation to light and gravity, as well as their interaction, in 25 populations of Trichogrammafrom five species. We show that most Trichogramma populations and species harbour preferences for light and preferences for elevated parts. However, the two traits harbor significant inter and intraspecific variation. The effects of light and gravity on oviposition patterns were found to be almost perfectly additive overall, with two exceptions. Ovipositionpreference patterns were not static but very plastic in time: preferences tended to relaxover consecutive days, and the strongest preferences relaxed the fastest, presumably because of the density-dependent effect of resource depletion. A correlation of ovipositionpatterns with the vegetation stratum at which populations were sampled suggests thatdifferent species/populations may be associated with different strata with correspondingdifferentiation in light- and gravity-related oviposition preferences.