Evaluation of intraguild interactions between two species of insect herbivores on Pistia stratiotes

• Neohydronomus affinis and Lepidelphax pistiae are specific to waterlettuce.
• N. affinis is a successful biocontrol agent in some areas but more agents are required in others.
• Performance of L. pistiae and the potential for interference of both species were tested.
• L. pistiae and N. affinis affected growth of waterlettuce and N. affinis caused a fall in L. pistiae populations.
• L. pistiae may be compatible for release in areas where N. affinis is present.

Pistia stratiotes L. (Araceae) is an important weed in many waterways around the world. The South American weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) is a successful biocontrol agent for this weed but additional agents are needed for some areas. The planthopper Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae) is a specific herbivore of P. stratiotes and is highly damaging in laboratory conditions. A field experiment was designed to evaluate the damage potential of L. pistiae compared to N. affinis and to assess the potential for competition between the two herbivores. Both herbivore species were reared inside floating cages on a P. stratiotes-infested lake. Plant growth indices assessed were clonation levels, biomass and plant diameter. The growth indices of plants exposed to the herbivores, individually and combined, were comparable, and significantly lower than in the control treatments. Population levels of N. affinis inside the cages were not significantly different when alone or together with L. pistae. Conversely, the density of L. pistiae was significantly lower in combination with the weevil. This suggests that L. pistiae is a damaging herbivore that will not reduce the biological control effectiveness of N. affinis.

Figure optionsDownload as PowerPoint slide