Influence of insecticide application timing on the field efficacy of chemical treatments against Agonoscena pistaciae (Hemiptera: Psyllidae)

Short paper

Influence of insecticide application timing on the field efficacy of chemical treatments against Agonoscena pistaciae (Hemiptera: Psyllidae)

Mehran Rezaei^1*, Fatemeh Graily-Moradi² and Mohammad Ali Mirhosseini³

1. Department of Plant Protection and Production, Institute of Agriculture, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran.

2. Postdoctoral Researcher, Department of Plant Protection, University of Tehran, Tehran, Iran.

3. Department of Plant Protection, Faculty of Agriculture and Natural Resources, Persian Gulf University, Bushehr, Iran.

Abstract: The pistachio psyllid, Agonoscena pistaciae Burckhardt & Lauterer, is one of the most destructive pests of pistachio trees in Iran. This study evaluated the efficacy of five chemical compounds including abamectin (EC 1.8%), acetamiprid (SP 20%), hexaflumuron (EC 10%), hexaflumuron (EC 10%) + abamectin (EC 1.8%), and thiamethoxam (SC 24%) at concentrations of 0.6 ml/L, 0.25 g/L, 0.7 ml/L, 0.5 + 0.3 ml/L, and 0.4 ml/L, respectively. The insecticides were applied at two different timings: early control (second week of May) and late control (fourth week of June) in two pistachio orchards in Isfahan Province, Iran. Nymphal mortality was recorded one day before spraying and at 3, 7, 14, and 21 days post-treatment. In both application times, thiamethoxam and abamectin exhibited the highest and lowest insecticidal efficacy, respectively. The early control was more efficient than the late control in all treatments. Therefore, early application of thiamethoxam is recommended for optimal chemical control of pistachio psyllid.

Keywords: Chemical control, Early control, Late control, Pistachio psyllid, Thiamethoxam

Introduction[1][2]

The pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Psyllidae), is a major destructive pest of pistachio trees, Pistacia vera L., in Iran (Hassani et al., 2009). Both nymphs and adults damage trees by feeding on plant sap, which weakens the trees, causes brown leaf spots, premature leaf and bud drop, reduces kernel weight, and increases blank and non-split nuts. These effects ultimately lead to significant declines in yield and quality (Tusun et al., 2024). According to FAO (2023), the United States was the global leader in pistachio production in 2023, yielding 675,850 tonnes. Iran, which possessed a larger cultivated area of 273,881 hectares (compared to 186,967 hectares in the U.S.), ranked second with an output of 307,866 tonnes. As pistachio represents a high-value crop, effective and timely pest control is critical. However, farmers often apply control measures haphazardly, including poorly timed interventions. Although chemical control remains one of the most effective strategies against A. pistaciae (Mehrnejad, 2010), the efficacy of insecticides heavily depends on application timing.

The pistachio psyllid requires multiple annual insecticide applications for effective control because it can complete up to 6 generations per year (Hassani et al., 2010; Mehrnejad, 2010). While adopting economic injury levels (EIL) can reduce pesticide use, determining accurate EIL thresholds is complex. Key challenges include the pest's unique feeding behavior, its multi-generational life cycle, varying cultivar susceptibility, and economic factors like input costs and market values. Field surveys indicate that approximately 95% of Iranian pistachio growers implement their first pesticide application during spring (March-June) following initial monitoring (Hosseininaveh & Abbasi, 2019).

To date, multiple classes of insecticides, including neonicotinoids and insect growth regulators (IGRs), have been registered in Iran for controlling psyllids and other pistachio pests (PPO, 2025). Several laboratory and field studies have documented the efficacy of various insecticides against A. pistaciae (Amirzade et al., 2014; Rouhani et al., 2019; Tusun et al., 2024). Given the pest's significant economic impact, Iranian farmers routinely use various insecticides to control A. pistaciae. Therefore, although abamectin is not registered for this pest, it was selected for this study because local growers commonly apply it. Since the optimal timing of insecticide application is crucial for successful pest control (Tang et al., 2010), this study aims to assess the field performance of five insecticides applied at two distinct timings for pistachio psyllid management.

Materials and Methods

In this study, the efficacy of five chemical compounds, including Abamectin (Vertimec^® EC 1.8%), Acetamiprid (Mospilan^® SP 20%), Hexaflumuron (Consult^® EC 10%), Hexaflumuron (Consult^® EC 10%) + Abamectin (Vertimec^® EC 1.8%), and Thiamethoxam (Memory^® SC 24%) was evaluated against pistachio psylla nymphs under field conditions. The tested concentrations were 0.6 ml/L, 0.25 g/L, 0.7 ml/L, 0.5 + 0.3 ml/L, and 0.4 ml/L, respectively. The insecticides were selected based on consultations with local agricultural advisors and producers in the study region. The experiment was conducted in two pistachio orchards located in Rahimabad village (32°46′N, 51°91′E, 1534 m) and Hosseinabad village (32°35′N, 52°16′E, 1572 m) in Isfahan province, Iran. The orchards consisted of 13-year-old Ahmadaghaei variety trees, which were uniformly managed for irrigation, fertilization, planting intervals, and crop load in accordance with regional standards. Chemical applications were timed for early (second week of May, Rahimabad) and late control (fourth week of June, Hosseinabad) in 2022. A randomized complete block design with five replications was employed. Insecticides were applied using a 20-L backpack engine-powered sprayer with a single-nozzle lance, and the sprayer was thoroughly cleaned between treatments. A water-only treatment served as the control. For sampling, five central trees per treatment were selected, and five compound leaves were collected from each tree at mid-canopy height from various directions. Nymphs of A. pistaciae on both leaf surfaces were counted and recorded. The economic injury threshold for this pest is reported as 20–30 nymphs per compound leaf (Tusun et al., 2024). Samples were transported to the laboratory in ventilated containers (11 × 10 × 4 cm), and live insects were counted under a stereomicroscope (20× magnification). Psyllid nymph populations were recorded one day before and 3, 7, 14, and 21 days after spraying (Mahdavian et al., 2021), without differentiation between nymphal stages. Efficacy was calculated using the Henderson-Tilton formula (1955). Normality of the data was assessed with the Kolmogorov-Smirnov test. Statistical comparisons were performed using one-way ANOVA (to assess differences in insecticide efficacy among treatments on a given sampling day) and an independent-samples t-test (to compare early and late control applications). Where ANOVA results were significant, means were separated using Tukey’s HSD test at P < 0.05. The data were analyzed using IBM SPSS Statistics v.22.0 (IBM Corp., 2013).

Results and Discussion

Table 1 presents the mean percent efficacy of abamectin, acetamiprid, hexaflumuron, hexaflumuron + abamectin, and thiamethoxam at 3, 7, 14, and 21 days post-application during mid-May (early control period). Among the tested insecticides, thiamethoxam exhibited the highest efficacy. The lethality of this insecticide was about 60% for up to 21 days after spraying, which was significantly higher than that of acetamiprid and abamectin. Abamectin showed the lowest insecticidal activity, and its combination with hexaflumuron did not significantly enhance hexaflumuron's toxicity. Notably, all insecticides (except abamectin) exceeded 70% efficacy against A. pistaciae for up to one week after spraying (Table 1).

During late control of psyllids, thiamethoxam and abamectin still exhibited the highest and lowest insecticidal efficacy, respectively; However, this difference was not statistically significant by 21 days post-treatment (Table 2). Furthermore, no significant differential efficacy was observed between the two neonicotinoids (thiamethoxam and acetamiprid) at any post-treatment interval. In contrast, when these insecticides were applied in mid-May (early-season control), their efficacy showed significant differences at 7, 14, and 21 days post-treatment (Table 1). The early control was more efficient than the late control in all treatments. This difference was particularly pronounced (statistically significant) at 3, 7, and 14 days post-treatment (Tables 1 and 2).

This study investigated temporal management strategies of pistachio psyllid control and their impact on the efficacy of recommended and commonly used insecticides. Our findings demonstrate that insecticide application timing significantly influences A. pistaciae control efficacy. Similarly, Abdolahi-Ezzatabadi et al. (2023) reported that temporal management knowledge for pistachio pests (including A. pistaciae) does not enhance pistachio yield but increases pesticide productivity and reduces application rate (0.477 l/ha/year). Indeed, optimizing application timing and the resulting increase in insecticide efficacy not only reduces spraying costs but also diminishes ecotoxicological impacts by reducing application volume or frequency (Abdolahi-Ezzatabadi et al., 2023).

Table 1 Efficiency of insecticides on nymphal stage of Agonoscena pistaciae at different days after spraying in Rahimabad village (middle May-early control).

¹ Means followed by different letters within each column are significantly different (P < 0.05, Tukey’s test).

² Days after treatment (DAT).

*Means marked with an asterisk indicate a significant difference between early and late controls at 5% level (using t-student test).

Table 2 Efficiency of insecticides on nymphal stage of Agonoscena pistaciae at different days after spraying in Hosseinabad village (late June-late season).

¹ Means followed by different letters within each column are significantly different (P < 0.05, Tukey’s test).

² Days after treatment (DAT).

*Means marked with an asterisk indicate a significant difference between early and late controls at 5% level (using t-student test).

Saour (2005) demonstrated that teflubenzuron (IGR) and thiacloprid (neonicotinoid) provided effective control of pistachio psyllid Agonoscena targionii Lichtenstein damage when applied early in the season. In contrast, mid-season kaolin-based coatings (when psyllid population pressure peaked) effectively reduced nymphal damage. Chemical control of psyllids is challenging under elevated temperatures because of their extended seasonal activity period, during which they undergo significant morphological, physiological, and behavioral adaptations (Saour, 2005). Furthermore, the diminished efficacy of late applications observed in the present study may be attributed to increases in pest populations and generational overlap during warmer months (Srinivasa Rao et al., 2022).

Abamectin (avermectin class) demonstrated consistently poor efficacy against A. pistaciae at both application timings across all evaluation periods (Tables 1 and 2). This limited performance likely results from abamectin's poor systemic activity and its mode of action. Abamectin exerts its effects by activating glutamate-gated chloride channels, leading to rapid paralysis in target insects (Wolstenholme & Rogers, 2005). In contrast, three effective insecticides were evaluated: thiamethoxam, acetamiprid (a neonicotinoid), and hexaflumuron (an IGR). These compounds have systemic activity with both contact and stomach effects. Neonicotinoids target nicotinic acetylcholine receptors, while hexaflumuron inhibits chitin formation and disrupts insect molting (Tunaz & Uygun, 2004; Simon-Delso et al., 2015). Tang et al. (2021) reported that thiamethoxam and acetamiprid exhibited high toxicity, whereas pyriproxyfen and buprofezin (IGRs) showed moderate toxicity against the Asian citrus psyllid, Diaphorina citri Kuwayama. Similarly, Bemani et al. (2018) compared the insecticide susceptibility of different populations of the pistachio psyllid and its predator (Oenopia conglobata L.) in Iran, finding that both insects were more sensitive to acetamiprid than to spirotetramat or hexaflumuron.

In the present study, field trials in Isfahan pistachio orchards (2022) revealed that application timing significantly alters insecticide efficacy against A. pistaciae. Specifically, early-season (mid-May) treatments with thiamethoxam achieved 90.97% nymphal mortality at 3 days post-treatment, whereas late-season (late-June) applications of the same insecticide yielded only 58.72%. Nevertheless, in pistachio orchards, early, mid, and late seasons are all critical periods for appropriate management due to the multivoltine life cycle and feeding behavior of this pest (Mehrnejad, 2013). Given the consistently low efficacy of abamectin across both application timings, it is recommended that growers exclude this insecticide from psyllid management programs. Substituting more effective alternatives (thiamethoxam, acetamiprid, and hexaflumuron) will prevent unnecessary costs and minimize the risk of insecticide resistance.

Acknowledgments

The authors gratefully acknowledge the Iranian Research Organization for Science and Technology (IROST) for its support. We also extend our sincere gratitude to Mr. Ghaffar Hajian and Mr. Hossein Dastanpour, pioneering pistachio farmers, for granting access to their orchards and facilitating the experimental work.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Conflict of Interest

The authors declare no conflict of interest.

Author's Contributions

Mehran Rezaei: Conceptualization, methodology, formal analysis, investigation, draft preparation, final review and edit, and project administration. Fatemeh Graily-Moradi: formal analysis, draft preparation, and final review and edit. Mohammad Ali Mirhosseini: formal analysis, draft preparation, and final review and edit.

References

Abdolahi-Ezzatabadi, E. M., Basirat, M. and Sedaghat, R. 2023. Investigation of the temporal management of pistachio pests control in Iran. Journal of Nuts, 14(1): 61-70. https://10.22034/jon.2022.1957605.1169.

Amirzade, N., Izadi, H., Jalali, M. A. and Zohdi, H. 2014. Evaluation of three neonicotinoid insecticides against the common pistachio psylla, Agonoscena pistaciae, and its natural enemies. Journal of Insect Science, 14(1): 35. https://doi.org/10.1093/jis/14.1.35.

Bemani, M., Moravvej, G., Izadi, H. and Sadeghi-Namaghi, H. 2018. Variation in insecticidal susceptibility of Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae), and its coccinellid predator, Oenopia conglobata L. (Coleoptera: Coccinellidae). Journal of the Kansas Entomological Society, 91(2): 110-118. https://doi.org/10.2317/0022-8567-91.2.110.

Food and Agriculture Organization of the United Nations (FAO). 2023. FAOSTAT: Crops and livestock products. Retrieved October 7, 2025, from http://www.fao.org/faostat/en/#
data/QCL.

Hassani, M. R., Nouri-Ghanbalani, G., Izadi, H., Shojai, M. and Basirat, M. 2009. Economic injury level of the psyllid, Agonoscena pistaciae, on pistachio, Pistacia vera cv. Ohadi. Journal of Insect Science, 9(1): 40. https://doi.org/10.1673/031.009.4001.

Hassani, M. R., Nouri-Ghanbalani, G., Izadi, H. and Shojaie, M. 2010. Population fluctuations of pistachio psylla, Agonoscena pistaciae (Hemiptera: Psyllidae), in Rafsanjan region. Iranian Journal of Plant Protection Science, 40: 93-98.

Henderson, C. F. and Tilton, E. W. 1955. Tests with acaricides against the brown wheat mite. Journal of Economic Entomology, 48(2): 157-161.

Hosseininaveh, H. and Abbasi, E. 2019. A survey of pistachio farmers' knowledge of pest status, economic injury Level and common pistachio pest control methods of pistachio orchards in Rafsanjan county. Journal of Pistachio Science and Technology, 4(7): 131-147.

IBM Corp. 2013. IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp.

Mahdavian, A., Dezianian, A. and Moharramipour, S. 2021. Effect of some botanical compounds on pistachio psylla Agonoscena pistaciae (Hemiptera: Psyllidae) under laboratory and field conditions. Journal of Crop Protection, 10(3): 447-459.

Mehrnejad, M. R. 2010. Potential biological control agents of the common pistachio psylla, Agonoscena pistaciae, a review. Entomofauna, 31(21): 317-340.

Mehrnejad, M. R. 2013. Pest problems in pistachio producing areas of the world and their current means of control. In VI International Symposium on Almonds and Pistachios 1028, pp. 163-169. https://10.
17660/ActaHortic.2014.1028.26.

PPO. 2025. Registered Insecticides Until the End of March 2025, Iranian Plant Protection Organization, https://www.ppo.ir/_douran
portal/documents/control-afat, pdf. 20 p.

Rouhani, M., Samih, M. A., Gorji, M. and Moradi, B. H. 2019. Insecticidal effect of plant extracts on common pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae). Archives of Phytopathology and Plant Protection, 52(1-2): 45-53. https://doi.org/10.1080/0323
5408.2019.1570589.

Saour, G. 2005. Efficacy of kaolin particle film and selected synthetic insecticides against pistachio psyllid Agonoscena targionii (Homoptera: Psyllidae) infestation. Crop Protection, 24(8): 711-717. https://doi.org
/10.1016/j.cropro.2004.12.007.

Simon-Delso, N., Amaral-Rogers, V., Belzunces, L. P., Bonmatin, J. M., Chagnon, M., Downs, C. and Wiemers, M. 2015. Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites. Environmental Science and Pollution Research, 22(1): 5-34. https://doi.org/10.1007/s11356-014-3470-y.

Srinivasa Rao, M., Mani, M., Prasad, Y. G., Prabhakar, M., Sridhar, V., Vennila, S. and Singh, V. K. 2022. Climate change and pest management strategies in horticultural and agricultural ecosystems, In: Mani, M. (eds) Trends in horticultural entomology. Springer, Singapore, pp. 81-122. https://doi.org/10.
1007/978-981-19-0343-4_3.

Tang, S., Tang, G. and Cheke, R. A. 2010. Optimum timing for integrated pest management: modelling rates of pesticide application and natural enemy releases. Journal of Theoretical Biology, 264(2): 623-638. https://doi.org/10.1016/j.jtbi.2010.02.034.

Tang, T., Zhao, M., Wang, P., Huang, S. and Fu, W. 2021. Control efficacy and joint toxicity of thiamethoxam mixed with spirotetramat against the Asian citrus psyllid, Diaphorina citri Kuwayama. Pest Management Science, 77(1): 168-176. https://doi.org/10.1002/ps.6004.

Tunaz, H. and Uygun, N. 2004. Insect growth regulators for insect pest control. Turkish Journal of Agriculture and Forestry, 28(6): 377-387.

Tusun, A., Kalkan, Ç. and Satar, S. 2024. Effects of some insecticides on Agonoscena pistaciae Burckhardt & Lauterer (Hemiptera: Psyllidae). Turkish Journal of Agriculture-Food Science and Technology, 12(s1): 2082-2088. https://orcid.org/0000-0003-4492-120X.

Wolstenholme, A. J. and Rogers, A. T. 2005. Glutamate-gated chloride channels and the mode of action of the avermectin/milbemycin anthelmintics. Parasitology, 131(S1): S85-S95. https://doi.org/10.1017/S0031182005008218.