African weaver ant-produced semiochemicals impact on foraging behaviour and parasitism by the Opiine parasitoid, Fopius arisanus on Bactrocera invadens (Diptera: Tephritidae).
The fruit fly, Bactrocera invadens is an alien invasive pest of mango in Africa. The predatory African weaver ant, Oecophylla longinoda is being promoted for managing B. invadens and classical biological control with the Opiine parasitoid, Fopius arisanus is also underway. The current study investigated interactions between these two natural enemies. Specifically we assessed whether semiochemicals deposited by the ant on leaves and fruit affected the landing behavior of F. arisanus, its patch residence time and subsequent parasitism rates. Results showed that significantly more F. arisanus landed on 'ant-unexposed' leaves and fruits (leaves: 3.8±0.5-7.7±0.8; fruits: 4.1±0.1-8.1±1.2) compared with 'ant-exposed' leaves and fruits (leaves: 0.4±0.1-2.5±0.3; fruits: 0.2±0.1-2.8±0.7) from mango, citrus, guava and avocado. Parasitoid patch residence times were significantly longer on 'ant-unexposed' mango fruits (654.2±28.4 s-1034.2±112.6 s) compared to 'ant-exposed' fruits (75.2±18.4 s-144.8±42 s) regardless of whether eggs of B. invadens were present. In terms of percent parasitism, F. arisanus achieved significantly higher parasitism rates in B. invadens from 'ant-unexposed' mango fruits (72.8±3.8) compared with 'ant-exposed' fruits (18.2±1.8). Regression analysis showed a significant inverse relationship between the duration of exposure of mango fruits to ant-produced semiochemicals and the number of F. arisanus adults landing on fruits and percent parasitism. In field cages, 32% parasitism of B. invadens was achieved in mango fruits on trees without ants and 11% in mango fruits on ant-infested trees. These results suggest the potential for biotic interference between the two natural enemies if they are recommended for use within the same ecosystem.