To determine the dispersal of corn borer moths (one-generation, Z-strain), 12 black-light-traps were placed at emergence (wheat) and oviposition (first year maize) sites and at intermediary positions in grassland at a distance of at least 50 m from the emergence and oviposition sites.
At both the emergence and intermediary sites, up to 90% of trapped females were mated. Males out-numbered females significantly at the place of emergence (77%) but not in the maize fields (40%). Half of the females at the emergence sites were carrying eggs and a quarter of these were unmated. We therefore hypothesise that the dispersal flight for most females occurs after mating in the fields from which they had emerged and before the first oviposition. Males do not seem to perform such an adaptive dispersal.
Dissection revealed that 16-21% of the mated females contained more than one spermatophore. Females with one or two matings occured at all sites, but females with 3 spermatophores were found only in maize fields. Nomadism is characterised by intermittant oviposition among neighbouring fields, where additional matings take place.
Air temperatures below 13°C supress dispersal flights from maize or wheat fields, while appetitive flights for mating and oviposition within the vegetation layer are still possible because the higher temperature within the crop.