Citrus Leafminer, Phyllocnistis citrella (Lepidoptera: Gracillariidae), and Natural Enemy Dynamics in Central Florida During 2005

Marjorie A. Hoy, Raghuwinder Singh, Michael E. Rogers


After the citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), invaded Florida in 1993, the endoparasitoid Ageniaspis citricola Logvinovskaya (Hymenoptera: Encyrtidae) was introduced in 1994 in a classical biological control program. Subsequent to its establishment, only limited information has been obtained regarding the seasonal abundance of A. citricola and its host in central Florida citrus groves. During 2005, we monitored replicated plots treated with oil or imidacloprid once on 23 Jun 2005, along with untreated control trees, in a Polk County commercial Valencia orange grove on a weekly basis when tender new growth (= flush) was available. As expected, CLM abundance in the early spring flush was nearly undetectable due to the lack of suitable flush during winter when CLM populations decline nearly to zero. Also as expected, A. citricola was not found during this time. During the second flush (Jun through Jul) CLM populations increased and A. citricola appeared, parasitizing up to 39% of the pupae in the untreated controls and up to 33% in the blocks treated with oil. Imidacloprid did not significantly reduce the number of CLM larvae but did reduce Asian citrus psyllid, Diaphorina citri Kuwayama, nymphal densities. Peak abundance of the CLM occurred during the third flush cycle on 5 Oct from trees treated once with oil, with a mean (SD) of 1.3 (0.8) CLM mines per leaf. Parasitism by A. citricola increased through the season, peaking at 56% of the CLM that had pupated prior to the 16 and 23 Nov samples in the untreated control trees and at 37% in the oil-treated trees; A. citricola was not found in imidacloprid-treated trees on those dates. During the growing season, a high proportion (up to 100% in some samples) of the CLM mines were empty, presumably due to predation. The data confirmed, for the first time, that A. citricola is an important natural enemy of those CLM larvae that escaped predation in this citrus-growing area in Florida. Nymphs of the Asian citrus psyllid were significantly reduced for 3 weeks after the imidacloprid treatment. However, shoots on trees treated with imidacloprid were significantly shorter than shoots on untreated trees and the number of shoots produced in imidacloprid-treated trees was reduced, raising concerns that imidacloprid might affect growth of citrus flush. Brown citrus aphids were nearly absent throughout the growing season.

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