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

Abstract

Trichogramma are parasitic microwasps much used as biological control agents. The genus is known to harbor tremendous diversity, both inter- and intra-specific. The successful selection of appropriate strains rests on a careful evaluation of this diversity at the phenotypic level, especially regarding oviposition performance and behavior. Oviposition preferences in relation to environmental cues such as light and gravity, although suspected to play an important role in microhabitat selection and oviposition patterns, have received little attention so far in this group, either alone or in combination. The extent of their variability is thus virtually unknown. Here we use a novel experimental approach relying on automatic image analysis to characterize the oviposition preferences in relation to light, gravity, and their interaction, in 25 populations of Trichogramma from five species. We show that most Trichogramma populations and species harbour preferences for light and preferences for elevated parts. However, the two trait 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. Oviposition preference patterns were not static but very plastic in time: preferences tended to relax over consecutive days, and the strongest preferences relaxed the fastest, presumably because of the density-dependent effect of resource depletion. A correlation of oviposition patterns with the vegetation stratum at which populations were sampled suggests that different species/populations may be associated with different strata with corresponding differentiation in light- and gravity-related oviposition preferences.

When complex movement yields simple dispersal: behavioural heterogeneity, spatial spread and parasitism in groups of micro-wasps

“…The two host distributions thus had on average the same host density (120 eggs in total per arena). In those treatments the parasitism status of each egg at the end of the experiment was recorded: the bottom paper sheet was stored for five days at 25°C, after which parasitized hosts turned black and could be counted (see (Burte et al, 2022;Morel-Journel et al, 2016)).…”

“…Insects were reared on UV-sterilised eggs of Ephestia kuehniella (the common laboratory host for trichograms, also used for sampling and experiments) with a 12:12 light:dark cycle, at temperatures switching between 25°C and 19°C, in order to get a development time of 14 days from host parasitism to adult emergence (Burte et al, 2022). All individuals used for experiments were 24 hour old and kept at 25°C in a glass tube with water and honey as a facultative food source prior to experiments.…”