The black vine weevil can be a serious pest of many ornamentals used in commercial buildings. The white, legless larvae feed on plant roots and may kill plants when numerous. In areas catering to shoppers and diners surrounded by containerized plants, chemical control is difficult. Nematodes are effective against black vine weevil, but they may not persist in the containers for long-term control. Using an alternate host may enhance the nematode's potential as a biological control agent.
In an outdoor containerized planting of kangaroo ivy in San Francisco's Embarcadero, both Steinernema feltiae and Heterorhabditis bacteriophora reduced black vine weevil infestations to a very low level. Adding an alternate host (in this case larval waxworms which are not plant feeders) improved nematode persistence in the containers' soil after the first 70 days. However, the long persistence of both nematodes in treatments without the alternate host suggested that they were reproducing in black vine weevil larvae and pupae. In fact, there was no difference in black vine weevil populations in the treatments with or without the alternate hosts.
These experiments demonstrated that S. feltiae and H. bacteriophora can reproduce when suitable hosts are present in potted soil. However, the periodic addition of alternate hosts to boost nematode populations is probably not practical for commercial plantings where large numbers of containers are maintained for several years. More practical is regular monitoring for the presence of weevils and timely applications of nematodes to augment the existing nematode population for pest suppression.
Burlando, T. M., H. K. Kaya, and P. Timper. 1993. Insect-parasitic nematodes are effective against black vine weevil. Calif. Agric. 47(3): 16-18.
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