The role of detoxification enzymes in the susceptibility of Brevipalpus californicus exposed to acaricide and insecticide mixtures.

The intense spraying of pesticides to control different arthropod pests has resulted in negative side effects for the management of pests. It was previously discovered that exposure to non-acaricidal insecticides alone or in a mixture, results in lower efficiency of the acaricide spirodiclofen used for Brevipalpus spp. control. We investigate here whether the induced expression of detoxification enzymes by non-lethal insecticides may antagonize spirodiclofen toxicity. Brevipalpus californicus mites exposed to the insecticide phosmet alone or in combination with spirodiclofen showed increased activity of P450 monooxygenases (P450s). No antagonistic effects in mite mortality were observed by the combination of phosmet and spirodiclofen. On the other hand, mites exposed to the insecticide imidacloprid alone or in combination with spirodiclofen showed an increase in the activity of P450s, carboxylcholinesterases (CCE), and glutathione-S-transferases (GST). An antagonistic effect on mite mortality was observed when mites were exposed to the LC25 of spirodiclofen combined with the field rate treatment of imidacloprid. The addition of PBO (a P450 monooxygenase inhibitor) to the mixture of spirodiclofen and imidacloprid resulted in a synergistic effect over mite mortality but the addition of DEM (a GST inhibitor) resulted in an antagonist effect. Taken together, this study showed that the combination of imidacloprid with spirodiclofen is antagonistic for the control of B. californicus, and this results from the induction of detoxification enzymes, such as P450s, CCE, and GST. The use of inhibitors highlights the role of these enzymes in the antagonism of the mixture.

Sublethal effects of spirodiclofen on biological and demographic parameters of the citrus leprosis mite Brevipalpus yothersi (Acari: Tenuipalpidae).

BACKGROUND: Brevipalpus yothersi Baker is one of the main vectors of citrus leprosis. Knowing the biology of this mite species when under chemical control is extremely important to understand its population dynamics, and then to solve problems of management of this pest. Therefore, we assessed the effects of one sublethal dose of spirodiclofen (0.48 ppm) on biological and demographic parameters of B. yothersi under laboratory and greenhouse conditions, comparing them with non-exposed mite population. RESULTS: Under laboratory conditions, where citrus fruits were used as a substrate, the duration of developmental stages (pre-egg-laying and egg-laying) and mite longevity showed no differences between treatments. However, the number of laid eggs increased in acaricide-treated fruits. In the greenhouse experiment, where citrus plants were used as a substrate, the instantaneous growth rate (ri) of mites was positive in all untreated plots. In contrast, in treated plants, ri was negative in 12 experimental units, and mite populations were suppressed in five of them. Moreover, mite population dynamics had a positive ri in three treated plants. CONCLUSIONS: Spirodiclofen sublethal dose had no negative effect on the offspring of B. yothersi females. However, it is not safe for citrus leprosis mite since it may increase egg number per female in some conditions. Biological and demographic differences could influence mite population dynamics in the field, requiring appropriate management strategies to improve citrus leprosis control. © 2019 Society of Chemical Industry.

Carvacrol and linalool co-loaded in ß-cyclodextrin-grafted chitosan nanoparticles as sustainable biopesticide aiming pest control.

Pesticides are the main tactics for pest control because they reduce the pest population very fast and their efficiency does not depend on abiotic factors. However, the indiscriminate use of these substances can speed up the development of resistant populations and causing environmental contamination. Therefore, alternative methods of pest control are sought, such as the use of botanical compounds. Nanoencapsulation of volatile compounds has been shown to be an important tool that can be used to overcome the lack of stability of these compounds. In this work, we describe the preparation and characterization of chitosan nanoparticles functionalized with ß-cyclodextrin containing carvacrol and linalool. The toxicity and biological activity were evaluated. Decreases of toxicity were observed when the compounds were nanoencapsulated. The nanoparticles presented insecticidal activity against the species Helicoverpa armigera (corn earworm) and Tetranychus urticae (spider mite). In addition, repellent activity and reduction in oviposition were observed for the mites.

Publisher Correction: Chitosan nanoparticles functionalized with ß-cyclodextrin: a promising carrier for botanical pesticides.

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Interaction of spirodiclofen with insecticides for the control of Brevipalpus yothersi in citrus.

BACKGROUND: The mite Brevipalpus yothersi (Acari: Tenuipalpidae) is of great importance in citriculture because it is a vector of the disease citrus leprosis. The frequency of application of a combination of pesticides has increased because of an increase in the occurrence of economically important pests of citrus. However, the combined effect of acaricide and other insecticides targeting B. yothersi is unknown. The objective of this study was to evaluate the effect of a combination of spirodiclofen and other insecticides on the control of B. yothersi. RESULTS: Analysis using spirodiclofen alone resulted in 97.22% efficiency in the control of B. yothersi on day 7 after application. A combination of spirodiclofen with either phosmet or imidacloprid resulted in 55% and 59% efficiency, respectively. A reduction in the efficiency of mite control by up to 42% was observed when the mites were exposed to a combination of acaricide with other insecticides. CONCLUSIONS: Application of a combination of spirodiclofen with phosmet or imidacloprid compromises the efficiency of acaricide in the control of B. yothersi. © 2018 Society of Chemical Industry.

Chitosan nanoparticles functionalized with ß-cyclodextrin: a promising carrier for botanical pesticides.

Carvacrol and linalool are natural compounds extracted from plants and are known for their insecticidal and repellent activities, respectively. However, their low aqueous solubility, high photosensitivity, and high volatility restrict their application in the control of agricultural pests. The encapsulation of volatile compounds can be an effective way of overcoming such problems. Inclusion complexes between beta-cyclodextrin (ß-CD) and carvacrol (CVC) or linalool (LNL) were investigated. Inclusion complexes were prepared by the kneading method. Both complexes presented 1:1 host:guest stoichiometry and the highest affinity constants were observed at 20 °C for both molecules. The nanoparticles containing carvacrol and linalool had mean diameters of 175.2 and 245.8 nm, respectively and high encapsulation efficiencies (<90%) were achieved for both compounds. Biological assays with mites (Tetranychus urticae) showed that the nanoparticles possessed repellency, acaricidal, and oviposition activities against this organism. Nanoencapsulated carvacrol and linalool were significantly more effective in terms of acaricidal and oviposition activities, while the unencapsulated compounds showed better repellency activity. The nanoformulations prepared in this study are good candidates for the sustainable and effective use of botanical compounds in agriculture, contributing to the reduction of environmental contamination, as well as promoting the effective control of pests in agriculture.

Space-time variability of citrus leprosis as strategic planning for crop management.

BACKGROUND: Citrus leprosis is the most important viral disease of citrus. Knowledge of its spatiotemporal structure is fundamental to a representative sampling plan focused on the disease control approach. Such a well-crafted sampling design helps to reduce pesticide use in agriculture to control pests and diseases. RESULTS: Despite the use of acaricides to control citrus leprosis vector (Brevipalpus spp.) populations, the disease has spread rapidly through experimental areas. Citrus leprosis has an aggregate spatial distribution, with high dependence among symptomatic plants. Temporal variation in disease incidence increased among symptomatic plants by 4% per month. CONCLUSIONS: Use of acaricides alone to control the vector of leprosis is insufficient to avoid its incidence in healthy plants. Preliminary investigation into the time and space variation in the incidence of the disease is fundamental to select a sampling plan and determine effective strategies for disease management. © 2018 Society of Chemical Industry.

The influence of citrus rootstocks on the relationship between the mite Brevipalpus phoenicis and citrus leprosis disease.

BACKGROUND: Leprosis is one of the most serious citrus plant diseases. Leprosis-affected plants, especially sweet orange [Citrus sinensis (L.) Osbeck], which is the most widely cultivated citrus fruit worldwide, show reduced photosynthetic capacity and severe defoliation. The aim was to evaluate the relationship between the Brevipalpus phoenicis (Geijskes) vector mite and citrus leprosis disease in Pera sweet orange plants grafted on different rootstocks. Data were analysed using numerical classification and conventional statistical analysis (ANOVA). RESULTS: Both viruliferous and non-viruliferous B. phoenicis populations increased in number on plants maintained at low soil water content. Among the evaluated rootstocks, Sunki mandarin proved least favourable for mite population increase. Furthermore, the viruliferous mite population increased more rapidly than the non-viruliferous mite population. CONCLUSION: The Cleopatra rootstock showed low variability in leaf nitrogen content, low mite number and low leprosis severity, thereby producing the most favourable results. Under appropriate moisture conditions, the Sunki rootstock produced the best results, showing the least severe leprosis. Rangpur lime rootstock grown in soil with varying water content showed the greatest variation in foliar nitrogen content, mite number and severity of leprosis and is considered to be the most difficult rootstock to manage.