Seasonal prevalence of the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) and its parasitoids in controlled and uncontrolled Citrus iyo groves in Ehime Prefecture, Japan

Abstract

Seasonal abundance and parasitism of the citrus leafminer, Phyllocnistis citrella Stainton were investigated in controlled and uncontrolled citrus groves from June 2001 through May 2002 on Citrus iyo (iyotangor) in Ehime Prefecture. No significant difference in mean monthly frequency of P. citrella infestation and its parasitoids was found between controlled and uncontrolled groves. There were two peaks of P. citrella infestation, in July and October. These peaks were strongly related to favorable temperature for P. citrella development and continuous flushing of new shoots. At least seven species of the parasite wasps of P. citrella were observed, of which Chrysocharis pentheus (Walker) and Sympiesis striatipes (Ashmead) were the predominant species. The population drastically increased from July to August, and also from October to November, which coincided with heavy infestation of P. citrella in the iyotangor grove. In spite of a high percentage of parasitism (about 70%) in summer and autumn, the damage to tender leaves was noticeable, because all native parasitoids attacked mature larvae and pupae of P. citrella after they had nearly completed their feeding period.

Toxicity of insecticides to the citrus leafminer, Phyllocnistis citrella, and its parasitoids, Chrysocharis pentheus and Sympiesis striatipes (Hymenoptera: Eulophidae)

“…However, several kinds of insecticides have been customarily applied to control other main pests such as thrips, longhorn beetle or scales. In our previous experiment, we could not find any differences in CLM infestation between controlled and uncontrolled groves (Mafi and Ohbayashi, 2004). Therefore, several insecticides for controlling CLM were registered and recommended to farmers, especially for use on young or top grafted trees or in greenhouses.…”

“…In the open fields of a citrus growing area in Ehime Prefecture, the CLM population started to increase from June and showed two peaks, from July to August and October to November (Mafi and Ohbayashi, 2004). The summer and autumn shoots of matured citrus trees, which are not fruit-bearing branches, are less important in spite of heavy infestation.…”

“…Later, he also described as "During the larval stage of the summer generation, 80% or more miners were killed by parasitoids and unknown factors" (Ujiye, 2000). In a district of Ehime Prefecture, two parasite wasps, Chrysocharis pentheus (endo-parasite) and Sympiesis striatipes (ecto-parasite) were the dominant species and occupied almost 80% of the natural enemy of CLM, and despite the parasitism of large larvae reaching 70%, the population density of CLM remained at a high level (Mafi and Ohbayashi, 2004). Both of these parasitoids lay eggs not on the first or second instar larvae but on the third instar larvae and prepupae.…”

“…But despite the rather high parasitism ratio, the population density of CLM remained at a high level (Mafi and Ohbayashi, 2004).…”

Seasonal dynamics, dispersion, sequential sampling plans and treatment thresholds for the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in a mature lemon block in coastal New South Wales, Australia

“…Thus, a sustained population growth of leafminer or even the maintenance of stable numbers is not possible without a sustained supply of new leaves. Flushing activity varies with season, and this would appear to be the main reason why populations fluctuate annually although this factor tends to be confounded with temperature and humidity (Mafi & Ohbayashi 2004). Simply correlating mine density with weather factors would be misleading because populations have to build up from a low base throughout spring; any correlations should be made with the rate of change in density rather than density itself.…”