Abstract
The carob moth (Ectomyelois ceratoniae) is the key pest of pomegranate, which causes a significant percentage of losses in pomegranate orchards and warehouses of Iran annually. The pest larvae are characterized by displaying a cryptic behavior within the fruit, which avoids most routine control techniques, especially chemical method. The low efficiency of traditional measurements and also the rich species diversity of natural enemies within the infested fruits highlight the necessity of exploring effective control methods, especially environmental friendly approaches. Entomopathogenic nematodes (EPNs) are a group of biological control agents that actively search for the host, including those in a cryptic habitat like the carob moth larvae within infested fruits. Here, we assumed that treatment of the infested and dropped fruits with EPNs may provide new insight into the management of the carob moth. Three species of EPNs, Steinernema feltiae, S. carpocapsae, and Heterorhabditis bacteriophora were selected and used in a series of in vitro and in vivo experiments. In preliminary assays, the EPNs species were used with different concentrations of infective juveniles (IJs) (0, 1, 5, 10, 25, and 50 IJ/larvae) in 2-cm diam. plates. The mortality rates of the laboratory tests were 79.75% and 76.5% for S. feltiae and S. carpocapsae, corresponded to LC50 value of 2.02 IJ/larva for S. feltiae and 2.05 IJ/larva for S. carpocapsae. On the contrary, H. bacteriophora demonstrated low virulence on the pest larvae in petri tests with a LC50 = 426.92 IJ/larva. Hence, both Steinernema species were selected for subsequent experiments. The penetration rate for S. feltiae and S. carpocapsae into the hemocoel of the pest was 43% and 31%, respectively, and the corresponding reproduction rate was 15,452 IJ/larva for S. feltiae and 18,456 IJ/larva for S. carpocapsae. The gathered data from those in vitro tests were used for a field assay. Different concentrations (5, 10, 50, 100, and 160 IJ/cm2 of the arena) of S. feltiae and S. carpocapsae were applied in the field test. The mean mortality results from the last test were 10.89% and 26.65% for S. feltiae and S. carpocapsae, respectively. Finally, we found that these low virulence rates of the nematodes were attributed to inhibitory/repellency effects of saprophytic fungi within the infested pomegranates, a usual status of the infested fruits in autumn or winter seasons. Future work on additional EPN populations more adapted to the extreme conditions of the pomegranate production area in Iran may provide sufficient evidence to continue the further investigation on the best EPN species populations and advanced formulations with high durability.
Highlights
The carob moth (Ectomyelois ceratoniae) is the key pest of pomegranate, which causes a significant percentage of losses in pomegranate orchards and warehouses of Iran annually
Pathogenicity assay of Entomopathogenic nematodes (EPNs) on the carob moth: To determine appropriate doses for future assays on the last larval stage, preliminary tests evaluated the susceptibility of last instar larvae of the carob moth to different concentrations of H. bacteriophora, S. carpocapsae, and S. feltiae
Pathogenicity assay of EPNs: The calculated LC50 of EPNs on the carob moth larvae in laboratory conditions were 2 infective juveniles (IJs) for both steinernematids, whereas it was 426.9 IJs/larva for H. bacteriophora (Table 1)
Summary
The carob moth (Ectomyelois ceratoniae) is the key pest of pomegranate, which causes a significant percentage of losses in pomegranate orchards and warehouses of Iran annually. Entomopathogenic nematodes (EPNs) are a group of biological control agents that actively search for the host, including those in a cryptic habitat like the carob moth larvae within infested fruits. Carob moth Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae) is the most important and destructive insect pest of pomegranate, an important fruit in parts of Asia (Sarkhosh et al, 2006) This pest causes quantitative and qualitative damage up to 80% in orchards and storehouses of Iran, which is the world’s top pomegranate producer (Shakeri, 2004). The third part of the study explored the efficacy of EPNs on the infested fruits under field conditions; the last test was designed to understand the migration behavior of the EPNs toward the pest larvae in heavily infested fruit and to identify effective species adapted to the pomegranate fruit
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