Distribution and Sampling of Bemisia argentifolii (Homoptera: Aleyrodidae) and Eretmocerus eremicus (Hymenoptera: Aphelinidae) on Cantaloupe Vines

Studies were conducted to examine the spatial distribution of immature Bemisia argentifolii Bellows & Perring and immature Eretmocerus eremicus Rose & Zolnerowich on cantaloupe vines and to develop efÞcient sampling plans. More B. argentifolii eggs were found on the 3rd leaf from the terminal of a cantaloupe vine than on any other leaf. The density of whiteßy nymphs peaked at leaf position 8, whiteßy pupae (large 4th instars) peaked at leaf position 11, and immature E. eremicus peaked at leaf position 14. We looked at 4 parameters to describe the distribution of whiteßy and parasitoid life-stages among the various leaf positions as follows: (1) median leaf position, (2) the leaf position with the highest percentage of a particular stage, (3) the leaf position where insect counts were best correlated with counts on the entire vine, and (4) the coefÞcient of variation (CV). All 4 distribution parameters changed throughout the season. In general the leaf positions described by the 4 distribution parameters increased (i.e., were further from the terminal) until themiddle of the seasonwhen theybegan todecline.Across the entire season, the 4distribution parameters for whiteßy eggs were associated with leaf positions 3, 4, and 5; for whiteßy nymphs with leaf positions 7, 8, and 10; for whiteßy pupae with leaf positions 11 and 12; and for immature parasitoids with leaf positions 11, 13, and 14. Based on considerations of cost and precision, it was most efÞcient to sample leaf 3 forwhiteßy eggs, leaf 8 forwhiteßy nymphs, leaf 11 forwhiteßy pupae, and leaf 14 for immature parasitoids. Using the Taylor power law, density-dependent minimum sample sizes (number of leaves per Þeld) necessary to achieve a predetermined statistical precision (mean 6 SE) were estimated. Over a broad range of densities, 50 leaves per Þeld are adequate to achieve a precision of 0.20Ð0.25 for all life stages. We also provide estimates of the optimum number of leaves to collect per vine based on the within-vine and between-vine variability and the costs (time) associated with counting whiteßies and moving to another vine.