Risk-spreading larviposition behaviour of female nose bot flies (Cephenemyia) attacking black-tailed deer.

While baited deer models were under observation nine Cephenemyia jellisoni Townsend (Diptera: Oestridae) females and seven C. apicata Bennett & Sabrosky engaged in a risk-spreading larviposition behaviour by larvipositing on models only once and then flying away. Additionally, analysis of 225 unobserved larvipostions in which larvae were trapped in adhesive on the muzzles of deer models showed that 94% of C. apicata and 95% of C. jellisoni larviposited on a model only once. The number of single larvipositions was highly significant for both species. The principal adaptive significance of such risk-spreading larviposition behaviour is that it spreads the reproductive output of a female among many hosts, and in years when adult eclosion and survival rates are low, it ensures that the larvae of the few surviving females will be distributed among a maximum number of hosts. Several other benefits of such behaviour also are discussed.