Effect of Nitrogen Fertility on Reproduction and Development of Citrus Mealybug, Planococcus citri Risso (Homoptera: Pseudococcidae), Feeding on Two Colors of Coleus, Solenostemon scutellarioides L. Codd

The effects of nitrogen concentration on the reproduction and development of citrus mealybug, Planococcus citri, were studied on two colors of coleus, Solenostemon scutellarioides. Green and red-variegated coleus plants were supplied with varying applied nitrogen concentrations (0, 25, 50, 100, 200, and 400 ppm) for 32 d before being artificially inoculated with citrus mealybugs. Female citrus mealybug life history parameters including eggs contained within the egg mass and respective body cavity, body length (mm), and developmental time (d) were measured. A modified micro-Kjeldahl digestion procedure followed by colormetric assay was conducted twice throughout the study to assess leaf nitrogen concentration. The results of this study show that the citrus mealybug life history parameters were influenced by the applied nitrogen concentrations (ppm), leaf nitrogen concentration (%), and total moisture content (g). Citrus mealybugs feeding on both green and red-variegated coleus, receiving the high nitrogen fertilizer concentrations (200 and 400 ppm) had the greatest egg loads, were larger in size, and had the shortest developmental times. Leaf nitrogen concentration also affected the citrus mealybug life history parameters with those mealybugs feeding on plants containing the highest leaf nitrogen contents having the greatest egg loads, larger in size, and the shortest developmental times. In addition, total plant moisture content impacted the citrus mealybug life history parameters similar to leaf nitrogen concentration. However, this was based on plant architecture whereas percent plant moisture content for both green- and red-variegated coleus was comparatively similar for all nitrogen concentrations. The life history parameters measured were more pronounced on green coleus compared with red-variegated coleus, perhaps because of nitrogen allocation differences between the two coleus colors. Thus, higher nitrogen concentrations, in the form of supplemental fertilizers used in greenhouse production systems, leads to an increase in the performance of citrus mealybugs as defined by increased egg loads, larger mature females, and shorter developmental times on coleus plants. These results indicate that the implementation of proper fertilizer practices may lessen the likelihood of dealing with extensive insect outbreaks, thus potentially reducing insecticide use.