Ant-Plant-Hemipteran Interactions Between Non-Native Species in Laikipia, Kenya

Abstract

Located in Laikipia County, beneath the shadow of Mt. Kenya, lies the Mpala Ranch property, a 48,000 acre plot of land consisting mainly of semi-arid savanna and acacia bushland. In addition to the diverse community of native flora and fauna that live on Mpala Ranch, there are also a number of invasive species that have disrupted the natural and human-made systems that characterize this ecosystem. In recent years, Mpala has attempted to limit the previously- unchecked sprawl of the invasive Opuntia stricta cactus by implementing widespread dispersal of the Opuntia-specific biocontrol insect, the Dactylopius opuntiae cochineal (Order: Hemiptera). My study seeks to determine whether another invasive species, the Pheidole megacephala big-headed ant (BHA) — which itself often interacts with honeydew-producing hemipterans — affects the biological control of O. stricta cacti via three-way ant-plant- hemipteran interactions (APHI). Controlled behavioral trials of invasive and native ants revealed no direct, resource-based relationships between the ants and the cochineal on O. stricta cacti. However, BHA showed high aggression towards the generalist herbivore Tenebrio molitor beetle, so it is possible that cochineal on O. stricta cacti in BHA invasion zones receive additional, advantageous protection. Furthermore, six-month manipulative outdoor, shared- greenhouse experiments suggested that BHA may also play a role in increasing the abundance of cochineal on infected cacti by promoting the settlement of new scale insect colonies on an individual host plant. Therefore, BHA could have non-trivial influences on cochineal abundance that would consequently extend to the control of O. stricta invasion. These results suggest that more research needs to be conducted on the possible APHI in this tripartite system.