A matter of antennal touch: timing and spatial selectivity of a tactually mediated, targeted oviposition behavior

Selective oviposition is a behavioral trait that requires detection and discrimination of potential sites followed by appropriate, sometimes spatially precise placement of eggs. In several lineages of stick and leaf insects (Phasmatodea), selective oviposition has evolved from a non-selective ancestral state, in which animals simply drop eggs to the ground. We herein describe such a selective behavior for Lobofemora sp., which places single eggs into small holes in front of its head and between the antennae, despite belonging to a lineage whose ancestral state has been reconstructed as dropping eggs. To test the hypotheses that such an egg placement involves antennal tactile detection and discrimination of site properties, we combined an oviposition assay with long-term motion tracking. We show that Lobofemora sp. employs its antennae for size-dependent site preference and postural adjustment according to directional properties of the site. Furthermore, we hypothesized and demonstrated that females refrain from egg-laying when no holes are available. We conclude that antennal tactile cues are sufficient to stimulate and inform targeted oviposition in Lobofemora. Because related egg-dropping species of the same lineage are unknown to use their short antennae for tactile exploration, we suggest that recruitment of the antennae for substrate probing was key to evolving this oviposition behavior.