Air potato (Dioscorea bulbifera L., Dioscoreaceae) is an herbaceous twining vine of Afro-Asian origin that was introduced into Florida around 1905. Since then it has aggressively invaded and smothered plant communities throughout the state, displaced native vegetation and disrupted ecological functions. Dioscorea bulbifera spreads via vegetative propagules (bulbils) produced annually at the leaf-axil and overwinters as underground tubers; vines senesce during late fall and sprout in the spring. Biological control of this weed has culminated in the release of a co-evolved beetle Lilioceris cheni (Coleoptera: Chrysomelidae) from South-Asia, which has established throughout the distribution range of D. bulbifera in southeastern U.S. Life-stage synchronies between the invasive plant and herbivore are expected to influence their interaction intensity and increase insect’s ability to affect target plant performance. Herein, we examined the synchrony between D. bulbifera and L. cheni life stages and influence on each other’s population densities and associated plant communities. We conducted two experiments: 1) 2-yr common garden study that documented vine growth, bulbil production and plant senescence prior to biocontrol, followed by 2) 5-year field studies in southern and northcentral Florida in which we gathered data on D. bulbifera vine cover and beetle damage and monitored changes in species richness.
Results/Conclusions
Normally, air potato bulbils and underground tubers begin to sprout in January in southern and February/March in northcentral Florida. Cover of trellising vines over other vegetation reached >50% by May and June in southern and northcentral areas, respectively and dropped to <20% by November. Aerial bulbil production began in June, peaked in September and continued into November. Overwintering adults of L. cheni in both regions began to emerge in April, attacked vines and laid eggs in May and continued thereafter. Larvae began to develop and feed on foliage in April and May in the south and north, respectively. Larval density peaked at 506 and 376 counts hr-1 by June in northern and southern regions. By July, the adult density counts hr-1 was twice as much in northcentral (430) than in southern (209) region, their density declined by November. Summarily, vine development occurred prior to adult emergence to start new colonies and the vines experienced sufficient feeding damage by June-July to suppress bulbil development and maturity. This synchrony between life stages of L. cheni and D. bulbifera caused >70% reduction in vine cover, >90% reduction in bulbil densities and 37% increase in plant species richness during 5-yr study period.