Population Dynamics of the Citrus Leafminer, Phyllocnistis citrella (Lepidoptera: Gracillariidae), and Its Natural Enemies in Texas and Mexico

The citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), was unreported in the western hemisphere until May 1993 when it was discovered in citrus nurseries in Florida. In Mexico, P. citrella was reported in 1994 in the state of Tamaulipas. Because of the potential threat to the citrus industries in both countries, a binational collaborative research project was initiated in 1997 to define and compare the status of P. citrella and levels of biological control between the two countries. In general, P. citrella populations increased in Mexico over the 3-year period from 1997 to 1999. In 1997, P. citrella peaked at ≈0.4 immatures/leaf in mid-October. In 1999, the pest began to increase in April, reaching peaks of ≈1.0 larva/leaf in early July. In both years, overall parasitism averaged ≈20%. The dominant parasitoid in Mexico was Zagrammosoma multilineatum (Ashmead) (Hymenoptera: Eulophidae), which constituted >30% of the parasitoid complex. Predators recovered were Chrysoperla spp. (Neuroptera: Chrysopidae), Orius insidiosus (Say) (Hemiptera: Anthocoridae), and Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae). In contrast, P. citrella generally declined in Texas over the same period. In 1997, the pest peaked at 0.8 immatures/leaf in August and did not exceed 0.4 immatures/leaf in 1998. The decline of P. citrella in south Texas is more evident when compared to a 1995 survey when pest densities exceeded 6.0 immatures/leaf. The monthly percentage parasitism of P. citrella in Texas increased from <1% in May to ≈10% in November 1997. In contrast, parasitism in 1998 fluctuated from 0 to 20%. Numbers of parasites were always <0.05 individuals/leaf and often zero. Similar to Mexico, the dominant parasitoid was Z. multilineatum, which constituted 46.2% (128 of 277) of the parasitoids sampled. Differences in P. citrella populations and those of its parasitoid complexes may be partially attributed to a hotter, drier climate in Texas than in Mexico.