Many lady beetles prefer aphids, but will feed on a variety of other foods. These alternative foods may serve only to maintain the predator and may not permit immature growth or adult reproduction. This was tested using two common lady beetles in alfalfa, Coccinella septempunctata and C. tranversoguttata, and alfalfa weevil larvae and sucrose as alternative foods. Field collected lady beetles from alfalfa were held in the laboratory and fed only alfalfa weevil larvae, or only pea aphids. Beetles fed only weevil larvae gained weight, but produced very few eggs, almost all of which were laid in the first few days. Beetles fed pea aphids gained weight and produced a normal number of eggs. Lady beetles fed only weevil larvae or sucrose solution were dissected and only very small immature eggs were found. However, when provided both weevil larvae and sucrose, beetles laid moderate numbers of eggs. These results indicate that weevil larvae may serve as an alternative food for these two lady beetles in alfalfa. Reproduction can occur in the absence of the preferred aphid prey if weevil larvae are combined with sucrose in the diet. Because plant nectars can serve as a natural source of sucrose in or near alfalfa fields, some reproduction by these lady beetles may occur in alfalfa fields infested with weevil larvae even if aphid numbers are low or absent.
D. R. Richards, and E. W. Evans. 1998. Reproductive responses of aphidophagous lady beetles to nonaphid diets: an example from alfalfa. Ann. Entomol. Soc. Am. 91: 632-640.
Streptomyces Suppresses Alfalfa Seedling Damping-Off
A disease-suppressive strain of Streptomyces that had been isolated from a potato field was evaluated for its ability to protect alfalfa seeds and seedlings during germination and emergence. Strain 93 inhibited the growth of soil-borne pathogens causing seed rot and seedling damping-off in Petri dish assays, but did not affect the growth of the nitrogen-fixing symbiont Rhizobium. In greenhouse tests, soil applications of Streptomyces at planting controlled Phytophthora root rot. In the field neither Streptomyces alone or the fungicide metalaxyl improved seedling establishment or disease control. However, the combination of fungicide and broadcast applications of Streptomyces improved plant establishment and increased the percentage of healthy plants. The following year, when Streptomyces was applied as a granular inoculum in furrow in combination with metalaxyl applied as a seed coating to approximate on-farm practices, there was no reduction in damping-off. A better understanding of how environmental conditions influence biocontrol is critical to developing strategies to improve disease control.
Jones, C. R, and D. A. Samac. 1996. Biological control of fungi causing alfalfa seedling damping-off with a disease-suppressive strain of Streptomyces. Biol. Control 7: 196-204.
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