A laboratory study investigating the combined effects of phosphorus and relative humidity upon reproduction by the European red mite Panonychus ulmi (Koch) was conducted. Phosphorus effects were tested at two levels (Hoagland solution with or without phosphorus) and relative humidity at five levels (6%, 30%, 60%, 75% and 90%). Experiments were run at two temperatures, 21°C and 25°C, and at a day-length regime of 16L:8D. The mites' response to phosphorus was characterized by a significant increase in progeny numbers when the host plant contained “high” levels of this element. Reaction to humidity was characterized by an increase in progeny at relative humidities between 60% and 75%. Under the same RH conditions, higher numbers of progeny were generally obtained from plants containing higher levels of phosphorus; the most favorable treatment was Hoagland solution with phosphorus and 75% RH.
Author notes
1 Part of a thesis submitted by the first author to the Graduate School of the University of Georgia in partial fulfillment of the requirements for a M.S. degree.
2 Graduate student and Professor respectively.