Numerical Responses of Natural Enemies to Artificial Honeydew in Utah Alfalfa

Abstract

Artificial honeydews were applied to alfalfa plots in field experiments during the second (1992) and third (1991 and 1992) crops in northern Utah. Individual plots received a single application of sucrose dissolved in water; protein supplement and water; sucrose, protein supplement, and water; or water alone. Sweep samples were taken for entomophagous arthropods over a period of 4 d (second crop) or 10 d (third crop) after treatment spray applications. Application of sucrose, but not of protein supplement, resulted in reduced densities of aphids (relative to those in plots sprayed with water only). Adult lacewings and lady beetles consistently responded positively to application of sucrose. Lacewings during the second and third crops in 1992 and lady beetles during the third crop in 1991 also responded positively to application of protein supplement, with greatest densities occurring in plots sprayed with both materials. Positive responses to application of sugar by adults of the alfalfa weevil parasitoid, Bathyplectes curculionis (Thomson), and adult hover flies, bigeyed bugs, and minute pirate bugs (but not spiders or adult damsel bugs) were also detected in one or more experiments. None of these groups, however, responded consistently or clearly to application of protein supplement. In the absence of rain, positive responses by particular natural enemies to sugar, protein supplement, or both, persisted for up to 7 d after application. Our experimental results add to those of previous research indicating that local populations of a variety of entomophagous insects, including parasitoids with non-aphid hosts, can be increased in crops by application of artificial honeydew.