The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is
the most devastating foliage-feeding pest of potatoes in the United States.
Potential biological control agents include the nematodes Heterorhabditis
marelatus Liu & Berry and Steinernema riobrave Cabanillas, Poinar &
Raulston, which provided nearly 100% CPB control in previous laboratory
trials. In the present study, laboratory assays tested survival and infection by
the two species under the soil temperatures CPB are exposed to, from 4-37°C.
H. marelatus survived from 4-31°C, and S. riobrave from 4-37°C. Both
species infected and developed in waxworm hosts from 13-31°C, but H.
marelatus rarely infected hosts above 25°C, and S. riobrave rarely infected
hosts below 19°C. H. marelatus infected an average of 5.8% of hosts from 13-
31°C, whereas S. riobrave infected 1.4%. Although H. marelatus could not
survive at temperatures as high as S. riobrave. H. marelatus infected more
hosts so is preferable for use in CPB control.
Heterorhabditis marelatus rarely reproduced in CPB. Preliminary
laboratory trials suggested the addition of nitrogen to CPB host plants
improved nematode reproduction. Field studies testing nitrogen fertilizer
effects on nematode reproduction in CPB indicated that increasing nitrogen
from 226 kg/ha to 678 kg/ha produced 25% higher foliar levels of the alkaloids
solanine and chaconine. However, the increased alkaloids did not affect
nematode infection of, nor reproduction in, CPB prepupae. Nematodes applied
to field plot soil at 50 infective juveniles/cm² reduced adult CPB by 50%, and
increased numbers of dead prepupae in soil samples up to five times more than
in non-nematode plots.
Laboratory studies of H. marelatus and its symbiotic bacteria in CPB
hemolymph indicated that immune responses did not limit nematode
reproduction. A 58kD CPB hemolymph protein apparently caused the
symbiotic bacteria to switch to the secondary form, which does not produce
antibiotics and enzymes necessary for nematode growth and reproduction.
Despite heat denaturation of the protein, the nematodes did not reproduce
unless lipids were added to the hemolymph. Therefore, while H. marelatus
may provide high levels of CPB control, nutritional constraints on the
nematode and its bacteria inhibit reproduction in CPB and limit long-term
multi-generation control. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30205 |
| Date | 28 August 2002 |
| Creators | Armer, Christine Andrea |
| Contributors | Berry, Ralph E., Rao, Sujaya |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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