Factors influencing adult female oviposition in the citrus leafminer Phyllocnistis citrella

1 The citrus leafminer (CLM) Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) is a serious pest in most citrus-growing regions of the world. The influence of leaf length, citrus species or variety, leaf colour tone and temperature on CLM oviposition was studied from field observations and laboratory experiments. The spatial distribution of eggs on leaves was also examined. Field data were obtained from 1100 samples collected in eastern Spain for 7 years. 2 Significant differences in oviposition rate were found among citrus species in 'no choice' laboratory experiments. This tendency was not apparent in the field due to the confounding effect of such factors as the intensity of new flushes and adult CLM abundance. Leaf colour tone and air temperature in the range studied (18-27 degrees C) had no effect on CLM egg-laying. 3 The distribution of eggs among leaves was random for population densities lower than four eggs per leaf, but became strongly aggregated above this, when not all eggs could survive and complete development. 4 The CLM developmental stage found on leaves depended on the leaf length, and most of the egg-laying occurred only on leaves that were 10-25 mm long. These leaves had the highest CLM stages in the field and thus give the best estimate of CLM oviposition.