A glimpse into the compatibilities and conflicts between arthropods and fungal biological control agents of aquatic weed waterhyacinth

Abstract

Interspecific interactions play an important role in ecosystem functioning. Several biocontrol agents are being introduced for the control of invasive species like the aquatic macrophyte, waterhyacinth, Eichhornia crassipes, in the hope of improving the eco-friendly natural control mechanism. Due to their overlapping niches, interspecific interactions among the biocontrol agents is high and there is a paucity of information on possible positive or negative impact they may have on each other hence affecting the biocontrol. Therefore studies on their interaction become even more important. In order to understand such possibilities, three potential fungi, Fusarium oxysporum (FO), F. roseum (FR), Paradendryphiella salina (PS) and two host-specific arthropods Orthogalumna terebrantis (OT) and Neochetina bruchi (NB) were applied on water hyacinth plants singly and in various combinations (OT, NB, FO, FO + OT, FO + NB, FR, FR + OT, FR + NB, PS, PS + OT, PS + NB). Observations were made on percentage damage caused by these agents to water hyacinth. Biocontrol agents applied in combination had cumulative impact on the target weed. FO + NB and FO + OT treated plants showed enhanced damage percentage of about 90%, after 120 h. But FR + NB and PS + NB treated plants were far less damaged compared to when these agents were applied separately. PS also had a repelling effect on NB. Results of such interactions are often variable and less predictable, especially under field conditions. These results demonstrate the need for studies on biotic interactions among biocontrol agents, prior to release of the biocontrol agents of weeds.