Nursery, Greenhouse, and Landscape

Natural Enemy of Eucalyptus Borer Introduced in Southern California

The eucalyptus longhorned borer (ELB) was first detected in Orange County, CA in 1984 and posed a serious threat to eucalyptus trees throughout the state that are used extensively not only as landscape ornamentals, but also as windbreak trees and for use as pulpwood and fuelwood. Without any natural enemies to check its progress, this insect spread south and northward, killing thousands of trees.

In 1992, the parasitic wasp Avetianella longoi was imported from Australia by University of California - Riverside entomologists. This tiny black wasp parasitizes ELB eggs, which are laid in clusters under the bark on trees. The adult wasps have a flattened body that allows them to wriggle under loose bark to reach the ELB eggs. The larvae develop in their host egg for about two weeks, then chew a hole in the eggshell to emerge. As many as 5 wasps can complete their development in a single borer egg. Female wasps parasitize about 200 eggs during their approximately one month life span.

Wasps that were released in the summer of 1993 readily established and dispersed at a remarkable rate through the urban terrain. The following spring adult wasps reappeared, having successfully overwintered, probably as pupae inside their host egg shells. More than 121,000 more wasps were released at seven additional sites throughout the state during 1994 and 1995, and continued releases at other sites were planned.

This wasp shows considerable promise for suppressing ELB populations. It kills a high proportion of eggs, sharply curtailing the number of beetle larvae that survive to bore into trees. Combined with its strong powers of dispersal and efficient location of host eggs, this wasp should have a significant impact on ELB in California.

Source:

Hanks, L. M., T. D. Paine, and J. G. Millar. 1996. Tiny wasp helps protect eucalypts from eucalyptus longhorned borer. California Agriculture 50(3): 14-16.

Nematodes Deter Slugs

The parasitic nematode Phasmarhabditis hermaphrodita occurs naturally in the UK, where it has been developed as a commercial control for slugs. Researchers in the UK found that pest slugs can detect the presence of and avoid soil treated with these nematodes. Slugs fed and rested preferentially on the untreated halves of boxes of soil during a 12-day period. One slug species tested avoided soil treated with 38 nematodes/cm2 -- which is similar to the recommended rate for field application -- but was not repelled at lower nematode densities. Nematode movement in the soil in the boxes was minimal.

It may be possible to protect certain crops from slug damage by treating the area immediately around the sensitive plants with a narrow band of nematodes. This would deter slug feeding using far fewer nematodes than would be necessary for slug control by treating the entire soil surface. It is suggested this would be most effective for crops grown in widely spaced rows.

Although the nematode is not currently commercially available in the U.S., efforts are being made to have it approved for commercial use here.

Source:

Wilson, M. J., L. A. Hughes, D. Jefferies and D. M. Glen. 1999. Slugs (Deroceras reticulatum and Arion ateragg.) avoid soil treated with the rhabditid nematode Phasmarhabditis hermaphrodita. Biological Control 16(2):170-176.


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