Insecticidal efficacy of three benzoate derivatives against Aphis gossypii and its predator Chrysoperla carnea.

Plant-derived benzoates are known to have insecticidal and repellent activities, however, these effects have been evaluated thoroughly in only a few groups of insects. In this study, the insecticidal activities of three commercially available benzoates, methyl benzoate (MB), ethyl benzoate (EB), and vinyl benzoate (VB), were assessed against the cotton aphid, Aphis gossypii Glover, and its lacewing predator, Chrysoperla carnea Stephens. MB showed the highest contact toxicity against nymphs and adults of A. gossypii, as compared to those of EB and VB. Treatments with 1% MB, EB, and VB were 100.0%, 93.0% and 60.0% effective, respectively, against third-instar nymphs and 100.0%, 69.0%, and 39.0% effective, respectively, against adults of A. gossypii, as evaluated 24 h after application. A mixture of MB + EB showed higher efficacy than other benzoate combinations against A. gossypii. The efficacy of MB, EB, and VB against A. gossypii on cucumber plants under greenhouse conditions was 93.7%, 68.5%, and 56.6%, respectively. In addition, treatments with 1% MB, EB, and VB were 20.0%, 24.0%, and 12.0% effective, respectively, against first-instar larvae and 6.7%, 13.3%, and 6.7% effective, respectively, against adults of C. carnea at 24 h after treatment. Our results showed that the tested benzoates were less toxic to the predator C. carnea than to the pest A. gossypii. In addition, the aphid population was significantly lower in a treatment combining predation by C. carnea followed by use of 1% MB, compared with treatments of either 1% MB or predators alone. This study suggests that plant-derived benzoates are potential biopesticides for aphid control and are compatible with natural enemies in integrated pest management.

Effect of Plant Essential Oil Formulations on Bemisia tabaci MEAM1 (Gennadius) and Its Parasitoid Eretmocerus hayati (Zolnerowich and Rose).

Silverleaf whitefly (SLW), Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), consists of genetically diverse species known to cause significant destruction in many crops around the world. Nowadays, synthetic insecticides are a key component in the management of this pest. However, they also come with disadvantages, such as environmental pollution, pest resistance and recurrence, and toxicity to pollinators and natural enemies. Essential oils from aromatic plants and biocontrol agents may provide a new and safe alternative to synthetic chemicals. In this study, we assessed the lethal impact of three new plant essential oil formulations (referred to as F1, F2, and F3) against the developmental stages of B. tabaci and its parasitoid Eretmocerus hayati (Zolnerowich and Rose) (Hymenoptera: Aphelinidae). The tested formulations consisted of combinations of mustard oil and different surfactants. The formulations were effective against the eggs and nymphal stages of B. tabaci. At the highest concentration assessed (1.23%), F1 was the most effective formulation against the eggs, resulting in 85% mortality, whereas F2 was most effective against the nymphs (92.5% and 88.3% mortality for the young and old nymphs, respectively). However, adult mortality rates were below 40% for all the tested formulations. The range of median lethal concentration (LC50) values was between 0.65 and 1.05% for B. tabaci. The side effects of the three formulations were assessed against E. hayati, treated as parasitized nymphs of B. tabaci. At the highest tested concentration (1.23%), F2 and F3 resulted in 80% and 70% mortality of the parasitoids, respectively (classified as moderately or slightly harmful according to the IOBC), whereas F1 resulted in 17.5% mortality. As F1 was effective against SLW with minimal effects on the parasitoid, it is the most suitable formulation of those tested for use in an integrated pest management (IPM) program targeting the younger life stages of B. tabaci.

Evaluation of Lethal and Sublethal Effects of Methyl Benzoate on the Generalist Predator Orius laevigatus (Fieber).

Methyl benzoate (MBe), a volatile organic molecule, has been shown to have insecticidal effects on a variety of agricultural, stored products, and urban arthropod pests in recent investigations. However, the toxicity of MBe against nontarget organisms has rarely been investigated. This study investigated the lethal and sublethal effects of MBe on the generalist predator Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) via different exposure routes. This species is an important natural enemy of thrips, aphids, and mites in biological control programs globally. Acute toxicity bioassays conducted on O. laevigatus showed that the lethal median concentration (LC50) values of MBe for topical and residual toxicity were 0.73 and 0.94%, respectively, after 24 hr of exposure. Importantly, a sublethal concentration of MBe (LC30 = 0.51%) did not affect the survival and reproduction of O. laevigatus. In addition, prey consumption by O. laevigatus under different exposure conditions with varying densities of Aphis gossypii (Glover) (Hemiptera: Aphididae) adults demonstrated a good fit for a Type II functional response. The sublethal concentration of MBe did not affect the attack rate and handling time of O. laevigatus compared to untreated insects, nor did it affect the longevity and fecundity of O. laevigatus females. Thus, according to the International Organization for Biological Control, the sublethal MBe concentration for O. laevigatus is categorized as harmless and may be used in conjunction with this predator species for integrated control of many agricultural insect pests.

Temperature-Dependent Development Models Describing the Effects of Temperature on the Development of the Fall Armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae).

The fall armyworm Spodoptera frugiperda (J.E. Smith) is an economically important pest that recently invaded Africa and Asia; however, information regarding its biological capacity to establish itself in newly invaded environments is largely unknown. We investigated the effects of temperature on the development and survival of the invaded populations of S. frugiperda and selected mathematical models to evaluate its development in a new environment. S. frugiperda exhibited optimum survival and growth at temperatures between 28 °C and 30 °C. The lower and upper thermal thresholds for the egg-to-adult life cycle were 13.51 °C and 34.13 °C, respectively. We compared seven mathematical models and found that the Shi model was the most suitable for describing the temperature-dependent development rate of S. frugiperda. Therefore, the Shi mathematical model may be used to predict both the occurrence of particular developmental stages and the geographic distribution to implement measures for the management of S. frugiperda in agricultural fields.

Larvicidal Activity of Methyl Benzoate, a Volatile Organic Compound, Against the Mosquitoes Aedes albopictus and Culex pipiens (Diptera: Culicidae).

Methyl benzoate (MBe) is a volatile organic molecule found in various plants; it is used as an insect semiochemical. MBe also has a biorational insecticidal effect against various agricultural and urban arthropod pests. The present study was the first to assess the larvicidal potential of MBe against fourth-instar larvae of the mosquitoes Aedes albopictus (Skuse) and Culex pipiens (L.). A positive association was observed between MBe concentrations and larval mortality in both the species. The highest mortality recorded was 100% for Ae. albopictus and 56% for Cx. pipiens after 24 h of exposure to 200 ppm MBe. The lethal median concentration (LC50) values of MBe against fourth-instar larvae of Ae. albopictus and Cx. pipiens were 61 ppm and 185 ppm, respectively. These results suggest that MBe has great potential for use as an environmentally friendly larvicidal agent for mosquito control.

Evaluation of the Effect of Fungatol and Gamma-T-ol on the Emergence and Adult Parasitoid Survival of Mummies of Cotton Aphids Parasitized by Aphidius colemani.

Beneficial insects play a major role in controlling pest populations. In sustainable agricultural production systems, control methods compatible with integrated pest management (IPM) are preferred over broad-spectrum pesticides. EOs from aromatic plants may provide a new and safe alternative to synthetic chemicals. In this research, the efficacy of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem was evaluated against Aphidius colemani Viereck (Hymenoptera: Braconidae; Aphidiidae), the parasitoid of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae). Under laboratory and greenhouse conditions, five different concentrations of each formulation were applied to parasitized mummies and adult parasitoids. Results for parasitoid emergence from aphid mummies sprayed with different concentrations of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem in the laboratory and glasshouse showed that the formulations did not adversely affect adult emergence as rates above 60% were observed. For residual toxicity tests done by exposing adult parasitoids to a fresh, dry biopesticide film sprayed on glass plates, less than 20% mortality was observed after 48 h of exposure. Adult longevity tests revealed that the highest concentrations of some of the formulations evaluated were slightly toxic to A. colemani. According to the IOBC rating, our results indicated that most of the tested concentrations for each formulation were harmless to A. colemani. Based on the above results, it may be proposed that the formulations evaluated in this study are potential botanical pesticide candidates for incorporation into an IPM program.

Methyl Benzoate Is Superior to Other Natural Fumigants for Controlling the Indian Meal Moth (Plodia interpunctella).

The Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), is an insect pest that commonly affects stored and postharvest agricultural products. For the control of insect pests and mites, methyl benzoate (MBe) is lethal as a fumigant and also causes contact toxicity; although it has already been established as a food-safe natural product, the fumigation toxicity of MBe has yet to be demonstrated in P. interpunctella. Herein, we evaluated MBe as a potential fumigant for controlling adults of P. interpunctella in two bioassays. Compared to the monoterpenes examined under laboratory conditions, MBe demonstrated high fumigant activity using a 1-L glass bottle at 1 µL/L air within 4 h of exposure. The median lethal concentration (LC50) of MBe was 0.1 µL/L air; the median lethal time (LT50) of MBe at 0.1, 0.3, 0.5, and 1 µL/L air was 3.8, 3.3, 2.8, and 2.0 h, respectively. Compared with commercially available monoterpene compounds used in pest control, MBe showed the highest fumigant toxicity (toxicity order as follows): MBe > citronellal > linalool > 1,8 cineole > limonene. Moreover, in a larger space assay, MBe caused 100% mortality of P. interpunctella at 0.01 µL/cm3 of air after 24 h of exposure. Therefore, MBe can be recommended for use in food security programs as an ecofriendly alternative fumigant. Specifically, it provides another management tool for curtailing the loss of stored food commodities due to P. interpunctella infestation.

Susceptibility of Various Developmental Stages of the Fall Armyworm, Spodoptera frugiperda, to Entomopathogenic Nematodes.

The fall armyworm, Spodoptera frugiperda, which is native to Central and South America, has recently invaded Africa and Asia, causing serious damage to various crops. Although management to date has been largely unsuccessful, entomopathogenic nematodes (EPNs) are a potential biological control agent that could be used to control the late larval and pupal stages of S. frugiperda that dwell under the ground. Here, we compared the virulence of seven EPNs against larval and pupal stages of S. frugiperda. In a Petri dish assay, both Heterorhabditis indica and Steinernema carpocapsae were highly virulent against younger larvae, whereas S. arenarium and S. longicaudum were highly virulent against older larvae. In contrast, H. bacteriophora, Heterorhabditis sp., and S. kushidai showed low virulence against all larval stages. In soil column and pot assays, H. indica, S. carpocapsae, and S. longicaudum were highly virulent against late larval and pupal stages compared with the other EPN species. Thus, H. indica, S. carpocapsae, and S. longicaudum are recommended for the biological control of S. frugiperda. Our study provides important information of EPNs for the practical application of biological control of fall armyworm.

Lethal and Sublethal Effects of Methyl Benzoate on the Predatory Bug Nesidiocoris tenuis.

Benzoates (naturally occurring plant toxins) produce pesticidal effects on various pest insects and mites, but their effects on non-target insects are poorly understood. In this study, we evaluate the lethal and sublethal toxicity of methyl benzoate (MB) to adults of the generalist predatory bug Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae). To assess lethal effects, N. tenuis was exposed to plant surfaces treated with 0.25%, 0.5% and 1% MB, as well as negative and positive controls (water and the neonicotinoid acetamiprid, respectively). Exposure to 1% MB resulted in the highest corrected mortality of 17.8% and 13.3% under laboratory and greenhouse conditions, respectively. Thus, 1% MB can be classified as harmless to N. tenuis according to the International Organization for Biological Control rating scheme. At the sublethal level, MB exposure did not significantly affect the consumption of eggs of the whitefly Bemisia tabaci by N. tenuis relative to negative control feeding rates. In contrast, acetamiprid at the manufacturer's recommended concentration reduced N. tenuis feeding activity by 45.4%. Furthermore, in a Y-tube olfactometer assay, there were no significant differences between the olfactory responses of N. tenuis to MB concentrations and the negative control (water). This study therefore suggests that MB could be used safely for pest control in combination with N. tenuis.

Acaricidal effects of methyl benzoate against Tetranychus urticae Koch (Acari: Tetranychidae) on common crop plants.

BACKGROUND: Methyl benzoate (MB) is a small, hydrophobic organic compound isolated from the freshwater fern Salvinia molesta (Salviniales: Salviniaceae). It is used as a fragrance and flavor enhancer owing to its pleasant smell. It has also demonstrated potential as a green pesticide for various groups of insects. However, its effects on mites are yet to be studied. RESULTS: Here, we assessed the acaricidal and repellent effects of MB against the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), under laboratory and greenhouse conditions. MB demonstrated concentration-dependent contact toxicity against eggs and adults of the mite. A leaf-dipping assay using 1% MB prevented the hatching of 92.7% of eggs and killed 100% of adults within 48 h of treatment. Concentration-mortality statistics were subjected to probit analysis, and the median lethal concentration (LC50 ) values for eggs and adults were 0.25% and 0.5%, respectively. Treatment with 1% MB showed the highest mortality (100%), with a median lethal time (LT50 ) estimated of 8.1 h. The efficacy of MB against adults of T. urticae on tomato plants under greenhouse conditions was 97.5% within 96 h post-treatment. Further, MB showed significant repellent activity against adult females of T. urticae, although this declined with time. Spraying with 1% MB (three times per plant) was not phytotoxic to bean, cucumber, pepper, or tomato plants. CONCLUSION: MB is highly acaricidal and repellent, but not phytotoxic, and is a promising green pesticide.

Evaluating cytotoxicity of methyl benzoate in vitro.

Methyl benzoate (MB) is a small, hydrophobic organic compound that is isolated from the freshwater fern, Salvinia molesta. Because of its pleasant odor, it has been used as a fragrance and flavor enhancer. In addition, it is used to attract orchid bees for pollination in the farm and has been tested for its potential to be developed as a green pesticide targeting a diverse group of insects. In spite of its wide applications, the safety of MB to humans remains poorly understood. In this study, we tested the cytotoxicity of MB against cultured human cells, including kidney, colon, and neuronal cells. Furthermore, other natural and synthetic benzoic acids such as ethyl benzoate (EB) and vinyl benzoate (VB) were compared with MB for their similarity and broad commercial and industrial applications. We found that MB and VB have the least and most overall toxicity to the tested human cells, respectively. In addition, the expression of some genes involved in cell cycle, protein quality control, and neurotransmission such as cyclin D1, HSP70, and ACHE genes was differentially expressed in the presence of these chemicals, most noticeably in treatment of VB. Our study provided the LC50 values of these benzoic acids for human cells in vitro and suggested their mild toxicity that should be considered in the industrial and agricultural applications to be within safe limits.