نوع مقاله : مقاله پژوهشی
نویسندگان
1 بخش تحقیقات کنترل بیولوژیک، موسسه تحقیقات گیاهپزشکی، سازمان تحقیقات، ترویج و آموزش کشاورزی، تهران، ایران.
2 بخش تحقیقات حشره شناسی موسسه گیاهپزشکی کشور، تهران، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Chemical control is generally the primary strategy to reduce damage caused by the tomato leaf miner, Phthorimaea absoluta (Lepidoptera: Gelechiidae). However, the implementation of alternative control approaches is essential. In the present study, the efficacy of the native entomopathogenic nematode isolate Steinernema carpocapsae IRMoghan1, metaflumizone, and their combined application was evaluated against larvae of P. absoluta within leaf mines. In a separate experiment, the effect of the insecticide on nematode survival was also assessed. According to the results, application of metaflumizone at 1000 ppm (98.3%) and the nematode alone (95%) resulted in the highest larval mortality, whereas the lowest mortality (52.5%) was observed at 250 ppm of metaflumizone. The combined application resulted in 86.7% pest mortality. Interaction analyses indicated an antagonistic interaction between the nematode and metaflumizone. Based on the compatibility assay, 24.28% mortality of infective juveniles was recorded after 72 h of exposure to the insecticide. According to IOBC/WPRS classification criteria, metaflumizone was categorized as harmless (Class 1) and compatible with S. carpocapsae IRMoghan1. The high mortality observed in the nematode treatment demonstrates its capacity to function effectively as a cruiser-type forager and to infect host larvae within leaf mines. One possible explanation for the observed antagonistic interaction, despite the classification of metaflumizone as harmless and compatible, is the already high level of mortality caused by the nematode alone, which may have limited the additive or synergistic effects in the combined treatment. Nevertheless, the underlying causes of the reduced efficacy of the nematode in combination treatments warrant further investigation.
کلیدواژهها [English]
Extended Abstract
Introduction
The tomato leafminer, Phthorimaea absoluta (Lepidoptera: Gelechiidae), is one of the most economically important pests of tomato crops in both open-field and greenhouse production systems. The entomopathogenic nematode Steinernema carpocapsae is among the most commercially utilized entomopathogenic nematode (EPN) species due to its favorable ecological and physiological characteristics. Traditionally, this species has been classified as an ambusher based on its host-seeking behavior. However, recent evidence indicates that it is capable of moving considerable distances toward hosts and may exhibit both ambushing and cruising foraging strategies, representing a significant advantage in managing pests inhabiting concealed or cryptic environments.The compatibility of entomopathogenic nematodes with insecticides is of considerable importance for tank-mix or simultaneous applications within integrated pest management (IPM) programs. Metaflumizone is a relatively new insecticide that has been increasingly used worldwide for the management of P. absoluta. The objective of this study was to evaluate the efficacy of the native isolate S. carpocapsae IRMoghan1 against larvae of P. absoluta and to determine its compatibility with metaflumizone. It was hypothesized that S. carpocapsae IRMoghan1 would exhibit cruising-like behavior, enabling it to infect larvae within leaf mines.
Larvae and pupae of P. absoluta were collected from an infested tomato field in Karaj and subsequently reared under greenhouse conditions. Tomato plants were used for insect rearing and bioassays.
First, the compatibility of S. carpocapsae IRMoghan1 with metaflumizone was assessed. A suspension containing 500 infective juveniles (IJs) per milliliter of distilled water was prepared and mixed with 150 mL of metaflumizone solution at the recommended field dose (1000 ppm). A similar IJ suspension in distilled water served as the control. Nematode mortality was recorded at 24, 48, and 72 hours after treatment. The experiment was replicated three times.
To evaluate the effects of the nematode and metaflumizone on P. absoluta larvae, potted tomato plants were placed inside an oviposition cage, and adult moths were released for 24 hours to allow egg laying. The plants were then transferred outside the cage to prevent further infestation. After 72 hours, when egg hatch and larval mine formation were confirmed, mined leaves were used for bioassays.Leaves were sprayed on both surfaces with a nematode suspension at a concentration of 30 IJs per cm², supplemented with Triton X-100 as a surfactant. Control leaves received the same volume of distilled water plus Triton X-100. Treated leaves were detached, and their petioles were placed in narrow 50 mL bottles filled with distilled water to maintain leaf freshness. To evaluate the insecticide effect, tomato plants were sprayed with metaflumizone at concentrations of 1000, 500, and 250 ppm using the same method as for nematode application. All bottles were maintained in a growth chamber at 25°C and approximately 90% relative humidity for 72 hours. Each treatment (including at least 60 larvae) was replicated three times on different days. After 72 hours, leaves were examined under a stereomicroscope, and the numbers of live and dead larvae were recorded. In nematode treatments, dead larvae were dissected to confirm nematode infection. The type of interaction between the nematode and metaflumizone was determined by comparing expected and observed mortality using the method of McVay et al. (1977) and Koppenhöfer and Kaya (1997).
Analysis of variance revealed a significant effect of exposure time on the mortality of infective juveniles treated with metaflumizone (df = 2, 8; F = 4.47; p < 0.05). The lowest nematode mortality (20.53%) was observed 24 hours after treatment, whereas the highest mortality (24.28%) occurred at 72 hours post-treatment. According to IOBC/WPRS classification criteria, metaflumizone was categorized as harmless (Class 1) and compatible with this nematode isolate. Significant differences were observed among treatments regarding larval mortality of P. absoluta (df = 2, 8; F = 11.51; p < 0.001). Based on mean comparisons, metaflumizone at 1000 ppm and S. carpocapsae IRMoghan1 applied alone resulted in the highest larval mortality, whereas metaflumizone at 250 ppm produced the lowest mortality. The calculated interaction parameters indicated an antagonistic interaction between the nematode and metaflumizone.
The compatibility of entomopathogenic nematodes with insecticides for tank-mixing or simultaneous application can reduce application costs and provide economic and environmental benefits. However, compatibility is species- and isolate-specific and must be evaluated prior to combining EPNs with any chemical insecticide. According to IOBC/WPRS classification, metaflumizone was harmless (Class 1) and compatible with S. carpocapsae IRMoghan1. Nevertheless, the observed antagonistic interaction—particularly at lower insecticide concentrations—necessitates further investigation into optimal nematode and insecticide concentrations and appropriate timing for combined application. Overall, the results demonstrated the high virulence of the native isolate S. carpocapsae IRMoghan1 against P. absolutalarvae. According to the host-seeking behavior framework proposed by Lewis et al. (2006), S. carpocapsae is traditionally classified as an ambusher. However, in this study involving P. absoluta larvae, the IRMoghan1 isolate exhibited cruising-like foraging behavior. Since the nematodes were applied to the leaf surface while larvae were feeding within leaf tissues, infective juveniles appeared to follow host-associated cues and penetrate leaf mines to infect the larvae. These findings suggest that host-seeking strategies in entomopathogenic nematodes may be flexible and adaptable to microhabitat conditions and host location, a characteristic that enhances their applicability against diverse pest species.
Conceptualization, Methodology, Data curation, Formal analysis, Writing, review & editing, Laleh Ebrahimi; Conceptualization and methodological design of the insecticide-related component of the study, Aziz Sheikhi. All authors have read and agreed to the published version of the manuscript.
Data will be available upon request.
This study presents partial results of a project conducted at the Iranian Research Institute of Plant Protection. The authors gratefully acknowledge the support provided by the Iranian Research Institute of Plant Protection and the Karaj Research Station of the Institute.
Not applicable.
The authors declare that they have no conflict of interest.
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