Concentration-mortality Bioassays Research Articles

Toxicity and Sublethal Effects of Piper hispidinervum Essential Oil on Behavioral and Physiological Responses of Sitophilus zeamais Populations.

This study aimed to evaluate the toxicity of Piper hispidinervum essential oil (PHEO) against 11 Brazilian populations of Sitophilus zeamais (Coleoptera: Curculionidae). The effects of sublethal doses of PHEO on the behavior (walking and flying), respiration, and population growth (ri) of the insect populations were investigated. PHEO toxicity was determined through concentration-mortality bioassays, with mortality curves established using increasing PHEO concentrations ranging from 140.00 to 1000.00 μL kg-1. Behavior was evaluated based on walking distance, walking time, walking speed, walking time proportion, flight height, and flight takeoff success. Respiration was measured via the respiratory rate, while population growth (ri) was assessed through the instantaneous growth rate. All 11 populations of S. zeamais were susceptible to PHEO, showing no signs of resistance. The populations exhibited varying behavioral and physiological responses to sublethal exposure to PHEO, indicating different mitigation strategies. The results confirm that PHEO possesses insecticidal potential for controlling S. zeamais populations. However, the observed behavioral and physiological responses should be considered when establishing control measures in pest management programs for stored products.

Is insecticide resistance a factor contributing to the increasing problems with Dalbulus maidis (Hemiptera: Cicadellidae) in Brazil?

The corn leafhopper, Dalbulus maidis, is an important pest in Brazil. While chemical control has traditionally been the cornerstone for managing this pest, field control failures have been reported for some insecticides. To understand if these failures are due to resistance, we evaluated the susceptibility of 11 field-collected populations of D. maidis to major insecticides during the 2021-2022 crop seasons in Brazil using concentration-mortality bioassays. Additionally, we employed diagnostic concentration bioassays and foliar sprays at label-recommended rates in 8-10 populations collected during the 2022-2023 crop seasons. High susceptibility to methomyl, carbosulfan and acephate was observed on concentration-mortality bioassays across all populations tested with resistance ratio (RR) based on LC50 <10-fold, except for one population from Bahia State that exhibited reduced susceptibility to methomyl (RR = 17.5). On the other hand, all populations exhibited reduced susceptibility to bifenthrin, acetamiprid, and imidacloprid, with RR ranging from 90 to 2000-fold. This reduced susceptibility to neonicotinoid and pyrethroid insecticides was further confirmed at diagnostic concentrations based on LC99 of the susceptible strain, with survival rates >20% and in foliar sprays with mortality rates <80%. Most populations exposed to acephate and carbosulfan exhibited low survival rates at diagnostic concentrations (<5%) and high mortality rates in foliar sprays (>80%). The reduced susceptibility to pyrethroid and neonicotinoid insecticides likely explain the field failures in controlling D. maidis populations in Brazil. This study represents the first large-scale susceptibility monitoring of D. maidis to insecticides, and the results will contribute to decision-making regarding the management of this pest. © 2024 Society of Chemical Industry.

Imidacloprid-resistant Aphis gossypii populations are more common in cotton-dominated landscapes.

Widespread reports of reduced efficacy of imidacloprid for managing cotton aphids (Aphis gossypii Glover) in cotton (Gossypium hirsutum L.) prompted an investigation to characterize the susceptibility of 43 populations over a 2-year period. The susceptibility of A. gossypii populations to imidacloprid was examined by calculating LC50 values. Further analyses related resistance assay results to a gradient of cotton production intensity. Concentration-mortality bioassays documencted populations that were 4.26-607.16 times more resistant than the susceptible laboratory population. There was a significant positive relationship between LC50 values and percentage of cotton within 2.5- and 5-km buffers surrounding collection sites. No significant relationship was detected between LC50 values and the percentage of alternative crop and noncrop hosts. Variable and high levels of resistance were detected in A. gossypii populations, and this variation was positively associated with cotton production intensity. Cotton is a host that may receive multiple applications of neonicotinoids (via seed treatment and foliar sprays) annually for seedling and mid-season pests. Rotating modes of action and limiting insecticide use should be implemented to delay the evolution of insecticide resistance in A. gossypii populations. © 2022 Society of Chemical Industry.

Phosphine Resistance in Turkish Populations of Sitophilus oryzae (L., 1763) (Coleoptera: Curculionidae)

In this study, the status of phosphine resistance in Sitophilus oryzae (L.,1763) (Coleoptera: Curculionidae) populations collected from Şanlıurfa, Adana and Kahramanmaraş province in Turkey were investigated by conducting the discriminating concentration tests and the concentration–mortality bioassays. Low (0.04 mg/L) and high (0.20 mg/L) discriminating concentration tests indicated that there was phosphine resistance of S. oryzae. The survival rates of field population of S. oryzae in Şanlıurfa, Adana and Kahramanmaraş ranged from 0 to 99%, 0 to 90% and 0 to 89% at the low discriminating concentration while it ranged from 0 to 83%, 0 to 46.5% and 0 to 28.5% at the high discriminating concentration respectively. Based on 50% mortality level (LC50), the Şanlıurfa 4, Adana 7 and Kahramanmaraş 8 populations were 57.5, 28.9, and 16.3 times more resistant, respectively, than the susceptible population (Kahramanmaraş 4). In conclusion, this study revealed that phosphine resistance in S. oryzae is high in the examined areas of Turkey and some populations have levels of resistance that may pose challenges to the continued use of phosphine for their management.

Incorporation of essential oil from Vitex gardneriana (Lamiaceae) in microemulsions systems based on mineral and cottonseed oils increased its bioactivity against a coconut pest mite

Coconut (Cocos nucifera L.) is an important cash crop for Asia, Africa and tropical America. The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae) is a major coconut pest, inflicting heavy damage to fruits, thereby reducing yields and farmers profitability. Previous research has demonstrated that high contents of sesquiterpenes compounds present in the essential oil of Vitex gardneriana Schauer (Lamiaceae) (EOVG) showed high potential to control A. guerreronis. Systems stabilized by surfactants, such as microemulsions (MEs), are promising to carry essential oils due to their solubilization and protection properties, generally allow for greater spreadability, wettability and have thermodynamic stability and lower viscosity. Here, we compared the acaricidal activity of MEs containing EOVG a based cottonseed oil (CO) and mineral oil (MO) as different oily phases. MEs formulations were obtained through the pseudoternary phase diagram using a 1:1 mixture of polysorbate 80: propylene glycol as surfactant and co-surfactant, respectively, and CO and MO as oily phases and water as aqueous phase. The MEs were characterized by polarized light microscopy, dynamic light scattering as well as by rheological behavior. Results based on concentration-mortality bioassays, showed that the toxicity of ME-CO containing EOVG was higher (LC50 = 195 ppm) in comparison with ME-CO without EOVG (LC50 = 669 ppm). Similarly, adding EOVG to ME-MO increased the toxicity further (LC50 = 120 ppm). Moreover, the LC50 of ME with and without EOVG for A. guerreronis was higher than the LC50 determined for the EOVG alone (LC50 = 888 ppm). The MEs containing EOVG in their LC80 and mainly LC50, repelled the mite. Overall, our results indicate that the MEs hold potential for controlling A. guerreronis, especially when EOVG was added with both oil phases.

Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) Fitness and Resistance Stability to Diamide and Pyrethroid Insecticides in the United States.

Simple SummarySpodoptera exigua is a polyphagous pest, commonly known as beet armyworm. This pest is distributed worldwide and causes yield reduction in a variety of crops. Chemical control using synthetic insecticides is the primary strategy to manage beet armyworm. In the United States, beet armyworm resistance to both chlorantraniliprole and bifenthrin insecticides was first reported in 2020. Here we examined beet armyworm fitness and stability of resistance to chlorantraniliprole and pyrethroid insecticides, since knowledge of the stability of resistance is a crucial aspect when recommending rotation of insecticides with different mode of action. Our results have indicated no decrease in bifenthrin resistance for at least a three-year period (i.e., 27 generations) when insecticide exposure was suspended. However, susceptibility to chlorantraniliprole dropped approximately 160-fold through this three-year period. Our results indicate that beet armyworm resistance to bifenthrin is stable, but unstable to chlorantraniliprole. Unstable resistance can be successfully managed at field level by switching off the selection pressure with replacement of the insecticide other than a pyrethroid.In the United States, beet armyworm resistance to both chlorantraniliprole and bifenthrin insecticides was first reported in 2020. Here we examined beet armyworm fitness and stability of resistance to chlorantraniliprole and pyrethroid insecticides since knowledge of the stability of resistance is a crucial aspect when recommending rotation of insecticides with different mode of action. Concentration-mortality bioassays were performed with field and laboratory susceptible populations. The F2, F13, and F27 generations of the field-derived population, maintained in the laboratory without insecticide, were exposed to commercial formulations of bifenthrin and chlorantraniliprole using the leaf-dip bioassay method (IRAC n. 007). Insects from F27 had the fitness components (survival, body weight, development time) documented and compared by LSM in each insecticide concentration tested. The resistance ratio to chlorantraniliprole reached 629, 80, 15-fold at F2, F13, and F27, respectively. These results contrast with an over 1000-fold resistance ratio to bifenthrin in all generations. The field-derived population had fitness reduced by chlorantraniliprole, but not by bifenthrin. In summary, the resistance of beet armyworm to bifenthrin was stable with no shift in fitness. In contrast, resistance to chlorantraniliprole was not stable through the generations kept in the laboratory without selection pressure, likely due to fitness cost.

New challenges demand new solutions: Selected essential oils as an alternative to control Bemisia tabaci MED in Brazil

The introduction of Bemisia tabaci Mediterranean (MED) (Gennadius) (Hemiptera: Aleyrodidae) (Biotype Q) into Brazil has attracted the attention of farmers and the scientific community as this species has a high capacity for infestation and high tolerance to conventional insecticides. As an alternative to chemical control, botanical derivatives stand out as a valuable tool for integrated pest management (IPM). In this context, this work evaluated for the first time the bioactivity of essential oils of Piper marginatum Jacq. (Piperaceae) (PM-EO) and Mansoa alliaceae (Lam.) A.ww H. Gentry (Bignoniaceae) (MA-EO) against B. tabaci MED. First, concentration-mortality bioassays were performed to estimate the lethal concentrations (LCs) on nymphs of B. tabaci MED. The LC50s and LC90s were tested in multi-choice assays (repellency and oviposition deterrence) and no-choice assays (ovicidal effects and infestation ability). Finally, assays were carried out in a greenhouse to check the efficiency of the essential oils under semifield conditions. The major compounds identified in PM-EO were (E)-methyl eugenol (34.7%) and (Z)-methyl eugenol (27.5%), while diallyl trisulfide (52.8%) and diallyl disulfide (33.9%) were the major compounds in MA-EO. The EOs were toxic against nymphs in the laboratory and greenhouse and showed ovicidal effect and repellent action. The EOs also reduced oviposition and inhibited the colonization by B. tabaci MED. Our results reveal two promising sources of botanical pesticides to control B. tabaci MED. These compounds can cause lethal and sublethal effects in all insect life stages, increasing the control efficiency.

Indoxacarb effects on non-target predator, Podisus distinctus (Hemiptera: Pentatomidae).

Forestry pest management includes biological and chemical methods of pest control. Using insecticides and natural enemies can be compatible in forest pest management programs. The compatibility of the predatory stink bug Podisus distinctus with the insecticide indoxacarb, used in forestry, needs to be evaluated in Brazil. This study investigated the mortality, survival, respiration, preference, prey consumption, and locomotor activity of P. distinctus adults exposed to indoxacarb. In concentration-mortality bioassays, the lethality of indoxacarb (LC50 = 2.62g L-1 and LC90 = 6.11g L-1) was confirmed in P. distinctus adults. The survival rate was 100% in predator insects not exposed to indoxacarb, declining to 40.7% in predator insects exposed to 2.62g L-1 and 0.1% in predators treated with 6.11g L-1. Indoxacarb reduced the respiration of P. distinctus from 18.45 to 14.41 µL CO2 h-1 at 2.62g L-1 for up to 3h after insecticide exposure, inhibiting food consumption and displaying hyperexcitation. The harmful effects of indoxacarb to the natural enemy suggest that it should be better assessed for use with P. distinctus for pest management in forestry.

Susceptibility of Demotispa neivai (Coleoptera: Chrysomelidae) to Beauveria bassiana and Metarhizium anisopliae entomopathogenic fungal isolates.

The potential of Beauveria bassiana and Metarhizium anisopliae isolates obtained from naturally infected oil palm pests was evaluated to control Demotispa neivai as an alternative for organophosphate insecticide use in oil palm crops in Latin America. Two B. bassiana (Bb-0018 and Bb-0025) and two M. anisopliae (Ma-0002 and Ma-0003) isolates were tested against D. neivai adults for hydrophobicity, virulence, survival, adhesion to host cuticle, and mortality in semi-field conditions. Concentration-mortality bioassays demonstrate that isolates had lethal effect on D. neivai adults with Bb-0025 [median lethal concentration (LC50 )=3.45 × 107 conidia mL-1 ] and Bb-0018 (LC50 =3.75 × 107 conidia mL-1 ) being the most effective followed by Ma-0003 (LC50 =3.38 × 108 conidia mL-1 ) and Ma-0002 (5.33 × 108 conidia mL-1 ). Adult survival was 99% without exposure to fungal isolates, decreasing to 21.65% in insects exposed to Ma-0002, 19.41% with Ma-0003, 20.13% with Bb-0018, and 0.17% with Bb-0025. Mortality of D. neivai adults caused by the entomopathogenic fungal isolates was similar in both laboratory and semi-field conditions. Also, vegetative growth of the entomopathogenic fungal isolates was found in infected D. neivai adults in the field. Our data suggest that the tested entomopathogenic fungal isolates are effective against D. neivai with potential to be used as biological control agents contributing to the decrease of the use of chemical insecticides to control this oil palm pest. © 2021 Society of Chemical Industry.

Control failure and insecticides resistance in populations of Rhyzopertha dominica (Coleoptera: Bostrichidae) from Colombia

The lesser grain borer Rhyzopertha dominica is a serious pest that causes significant economic damages in stored grains. The presence of this pest is mainly controlled using a small number of insecticides increasing risks of compromising the control efficacy due to the selection of resistant populations. Here, the control failure and potential resistance to pyrethroid and organophosphate insecticides frequently used for the control of R. dominica in Colombia were assessed. Concentration–mortality bioassays with synergized and unsynergized insecticides were used to assess potential metabolic-based pyrethroids resistance mechanisms. Based on the field recommended doses, the results revealed that while the pirimiphos-methyl is still efficient against R. dominica, both type I (i.e., bifenthrin) and type II (i.e., deltamethrin) pyrethroids presented control failure and their insecticidal activity was compromised. Although no differences in susceptibilities between the populations were found for the bifenthrin insecticide, the LC50s of Ibagué (1.83 μl/gr of grains) and El Espinal (1.67 μl/gr of grains) populations were higher than the recommended rate. Furthermore, significant differences in susceptibility to deltamethrin resulted in resistance ratios RR50 > 32-fold and RR95 > 188-fold between the least (El Espinal) and the most (Ibagué) susceptible populations. Moreover, when synergized, the toxicity of deltamethrin was enhanced but resistance ratios kept at high levels (RR50 > 11-fold and RR95 > 40-fold) indicating possible existence of simultaneous metabolic and altered action-site mechanisms of resistance to pyrethroids in Colombian populations. Our results highlight the urgent need for nationwide monitoring of insecticides control failure and resistance in stored pests for better management schemes.

Toxic effects of an essential oils mixture on Aleurodicus cocois (Hemiptera: Aleyrodidae) and Chrysoperla externa (Neuroptera: Chrysopidae)

ABSTRACT The whitefly Aleurodicus cocois is one of the main pests of cashew, Anacardium occidentale L. in Brazil. The use of essential oils and their constituents is an alternative means of controlling pests with low risk to natural enemies. In the present study, the chemical profile and toxicity of a mixture of the essential oils of Lippia sidoides Cham. (Verbenaceae) and Cymbopogon winterianum Jowitt. (Poaceae) on the third and fourth nymphal stages of A. cocois were evaluated, as well as their toxicity to the predator Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae). Thymol and ρ-cymene were the majority monoterpenes in L. sidoides oil, whereas in C. winterianus, geraniol, citronellal and citronellol oil were the main components. In the concentration-mortality bioassays, the toxicity of the mixture of the two essential oils evaluated on the third and fourth nymphal stages of A. cocois in terms of LC50 was estimated at 11.17 and 16.92 mg/mL, respectively. At all concentrations evaluated, the mixture of essential oils caused low mortality of C. externa eggs and larvae and did not alter predator development time. Additional repellency tests showed that independent of the tested concentrations and exposure times (1, 3, and 24 h), C. externa larvae were repelled by the mixture of essential oils. It is concluded that the mixture of the essential oils of L. sidoides and C. winterianum is toxic to nymphal stages of A. cocois and moderate toxicity to C. externa.

Effect of Benzoylphenyl Ureas on Survival and Reproduction of the Lace Bug, Leptopharsa gibbicarina

Simple SummaryPestalotiopsis fungal complex is a disease that causes damages in oil palm (Elaeis guineensis), and the lace bug, Leptopharsa gibbicarina is the main insect pest that spread this disease. Application of neurotoxic insecticides has been a common method used to control L. gibbicarina for decades in Colombia and Venezuela. The effects of four benzoylphenyl ureas (BPUs) (lufenuron, novaluron, teflubenzuron, and triflumuron) were assessed against L. gibbicarina for toxicity, survival, and reproduction. Overall, the results show that novaluron, teflubenzuron, and triflumuron cause high mortality and reduce survival time, fecundity, and fertility. Thus, BPUs exhibit detrimental effects on L. gibbicarina and can be used as alternatives to other chemical insecticides.The lace bug, Leptopharsa gibbicarina is a vector of Pestalotiopsis fungal complex in oil palm crops in the Americas. The effects of four benzoylphenyl ureas (BPUs) (lufenuron, novaluron, teflubenzuron, and triflumuron) were evaluated against L. gibbicarina for toxicity, survival, reproduction, and mortality in semi-field conditions. Concentration-mortality bioassays demonstrated that novaluron (LC50 = 0.33 ppm), teflubenzuron (LC50 = 0.24 ppm), lufenuron (LC50 = 0.17 ppm), and triflumuron (LC50 = 0.42 ppm) are toxic to L. gibbicarina nymphs. The survival rate was 99% in control nymphs, decreasing to 50% in nymphs exposed to LC50 of triflumuron, 47% in nymphs treated with lufenuron, 43% in nymphs treated with teflubenzuron, and 43% in those treated with novaluron. Sublethal concentrations of BPUs showed detrimental effects on the adult emergence, longevity, fecundity, and fertility of this insect. The mortality of nymphs caused by these insecticides was similar in both laboratory and semi-field conditions. Our results suggest that novaluron, teflubenzuron, and triflumuron are highly effective against L. gibbicarina, and therefore, have potential applications for this oil palm pest.

Contrasting susceptibility of lepidopteran pests to diamide and pyrethroid insecticides in a region of overwintering and migratory intersection.

Pesticide resistance is a growing issue worldwide, and susceptibility of pest populations should be monitored in migratory intersection regions for successful resistance management. We determined the susceptibility of eight noctuid species from the Florida Panhandle to bifenthrin (pyrethroid) and chlorantraniliprole (diamide). Larvae from field and laboratory populations were exposed to commercial insecticide formulations using the leaf-dip method in concentration-mortality bioassays. The field populations of Helicoverpa zea (Boddie), Spodoptera frugiperda (Smith), S. eridania (Stoll), S. exigua (Hubner) and Chloridea virescens (Fabricius) had reduced susceptibility to bifenthrin compared with the laboratory populations. Resistance ratios to bifenthrin were as high as 10 071-fold in S. exigua and 436-fold in S. frugiperda, while there was no reduced susceptibility in Agrotis ipsilon (Hufnagel). The susceptibility to chlorantraniliprole was similar between the field and laboratory populations studied, except for S. exigua that exhibited 630-fold resistance to the diamide. The probit regression equations indicated that the larval mortality of S. exigua and S. frugiperda populations was <80% with bifenthrin at the concentration equivalent to the label rate. Likewise, the estimated mortality of S. exigua larvae with chlorantraniliprole at the label rate concentration was <80%. The lepidopteran pest populations tested were variable in susceptibility to bifenthrin by contrast to more consistent susceptibility to chlorantraniliprole. These results help in the choice of effective insecticides for integrated pest management and resistance management in cropping systems colonized by migratory lepidopteran pests from the U.S. Gulf Coast region. © 2020 Society of Chemical Industry.

Field resistance of Plutella xylostella (Lepidoptera: Plutellidae) to lufenuron: Inheritance and lack of cross-resistance to methoxyfenozide

Plutella xylostella (L.), commonly known as diamondback moth, is one of the most important pests of Brassicaceae in Brazil. This study aimed to assess the susceptibility of P. xylostella and pattern of resistance inheritance to lufenuron, an insect growth regulator (IGR) that impairs the insect molting, as well as the cross-resistance to methoxyfenozide (Nonsteroidal ecdysone agonist). Concentration-mortality bioassays were performed using the leaf dipping method towards field collected populations and genotypes used in the genetic crossings. Populations of this pest, from the mesoregion of Pernambuco (Brazil), were highly resistant to lufenuron. The recommended concentration of lufenuron caused more than 80% mortality of larvae of two populations [Piedade (PDD) and Recife (REC-S)]. Methoxyfenozide caused more than 80% mortality of larvae of all assessed populations, suggesting no cross-resistance between insect growth regulators. The population of Bezerros (BZR-R) was the most resistant (11,283-fold) to lufenuron compared with REC-S population (standard reference). Resistance to lufenuron was inherited as autosomal, incompletely recessive, and monofactorial trait, suggesting that a single gene or a set of genes tightly linked is involved in resistance. Methoxyfenozide is an alternative molecule suggested for the control of P. xylostella in areas where resistance to lufenuron has evolved. Furthermore, information provided in this work should fine-tune insecticide resistance management (IRM) programs to delay the evolution of resistance to chitin synthesis inhibitors like lufenuron, where resistance frequency is incipient.

Lethal and sublethal effects of babassu and degummed soybean oils on the predatory mite Typhlodromus ornatus (Acari: Phytoseiidae)

ABSTRACTIn this work, the compatibility of the babassu and degummed soybean oils to Typhlodromus ornatus (Acari: Phytoseiidae) was evaluated through the integration of estimates of lethal concentration (LC) with non-lethal effects of repellency and population growth rate. Concentration-mortality bioassays showed that the babassu (LC50 = 5.03 μL/cm2) and degummed soybean oils (LC50 = 4.14 μL/cm2) were approximately 19 and 28 times less toxic to T. ornatus, respectively, in comparison to its prey Aceria guerreronis (Acari: Eriophyidae). Babassu oil was not repellent to T. ornatus, but the degummed soybean oil had a repellent effect at different concentrations and times of evaluation. Additional tests showed that regardless of the concentrations of the tested vegetable oil, the growth rate of T. ornatus was always positive. From the point of view of selectivity, babassu oil was more compatible with T. ornatus as it did not present repellency. We have concluded that both evaluated vegetable oils presented low risk to T. ornatus, and they are thus indicated as a promising tool to be integrated in management programmes to control A. guerreronis in coconut plantations.

Multiple insecticide resistance in onion thrips populations from Western USA

Thrips tabaci is a key pest of onions, especially in the Pacific Northwestern USA. Management of T. tabaci is dominated by the application of various insecticides. However, T. tabaci is known to develop insecticide resistance which possibly leads to control failures, crop loss, and environmental concern. Here, we evaluated resistance status of T. tabaci populations from conventional and organic commercial onion fields to three widely used insecticides: oxamyl, methomyl, and abamectin with on-field concentration-mortality bioassays. The biochemistry and molecular mechanisms underlying resistance to these insecticides were also investigated by using enzymatic assays and detecting resistance-associated mutations. Field-evolved resistance to oxamyl, methomyl and abamectin were detected in most of the T. tabaci populations collected from conventional onion farms. At the labeled field rate, all the tested insecticides, particularly methomyl and oxamyl, had significantly reduced efficacy. Enzymatic assays of insecticide target and detoxification enzymes indicated that T. tabaci populations in Western USA onions harbor multiple mechanisms of resistance including enhanced activities of detoxification enzymes and target site insensitivity. Our results provide new information in understanding the dynamics of T. tabaci adaptation to multiple insecticides, which will help to design sustainable insecticide resistance management strategies for T. tabaci. Furthermore, this study provides the foundation for future research in identifying the biochemical and molecular markers associated with insecticide resistance in T. tabaci.

Bioactivity of essential oil from Lippia gracilis Schauer against two major coconut pest mites and toxicity to a non-target predator

The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), and the red palm mite, Raoiella indica Hirst (Acari: Tenuipalpidae), are serious pests of commercial coconut plantations worldwide. We assessed the toxicity and sublethal effects of the essential oil from Lippia gracilis Schauer on these two pests, and its toxicity against Amblyseius largoensis (Acari: Phytoseiidae), a predatory mite that is mainly associated with R. indica. Chemical analyses revealed that the essential oil of L. gracilis accession LGRA106 contains thymol as a major compound (52.41%). Based on concentration-mortality bioassays, the toxicity of the oil differs from that of thymol for A. guerreronis (LC50 = 4.28 mg/mL, LC50thymol = 5.34 mg/mL) and for R. indica (LC50=4.99 mg/mL, LC50thymol = 9.03 mg/mL). The LC50, as estimated for R. indica, proved to be toxic to the predatory mite A. largoensis, killing roughly half of its population. In addition, the essential oil of L. gracilis and thymol, at their LC50 for each mite species, repelled A. guerreronis and reduced the survival and oviposition of R. indica. The potential of L. gracilis as a natural pesticide on coconut plantations and their effects on beneficial mites are discussed herein.

Toxic Activity of Pyrethroids in &lt;i&gt;Lutzomyia longipalpis&lt;/i&gt; (Diptera: Psychodidae) from Magdalena River Basin, Colombia

The study aimed to determine the toxicity of lambda-cyhalothrin, alpha-cypermethrin, and deltamethrin in L. longipalpis, through concentration-mortality bioassays. The test here was performed following WHO guidelines, but instead of using exposure WHO recipients and impregnated papers, 250 ml Wheaton glass bottles treated with 1 ml of insecticide solution were used. Batches of ten females of L. longipalpis were exposed to five concentrations of each pyrethroid that caused between 5 and 100 % mortality in this species. After 1 h of exposure, the females were transferred to observation recipients, and mortality was recorded 24 h later. The lethal concentrations (μg/ml) that killed 50 and 95 % (LC50 and LC95) of the exposed L. longipalpis females were 0.05 and 0.86 for lambda-cyhalothrin, 0.24 and 3.62 for alpha-cypermethrin and 0.53 and 4.72 for deltamethrin. Based on the LC50 obtained, lambda-cyhalothrin is the most toxic pyrethroid for L. longipalpis, followed by alpha-cypermethrin and deltamethrin. It is expected that these data may be useful in studies on the effects of sub-lethal concentrations of the three pyrethroids on the behavior of L. longipalpis and studies on the vector susceptibility to these pyrethroids.

Bioactivity of cottonseed oil against the coconut mite Aceria guerreronis (Acari: Eriophyidae) and side effects on Typhlodromus ornatus (Acari: Phytoseiidae)

The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), is a major pest of coconut plantations. In Brazil, the control of A. guerreronis, when accomplished, is heavily dependent on applications of conventional acaricides, which further increases the risks associated with pest resistance, hazards to human health and environmental contamination. Therefore, the development of alternatives to the chemical control concerns outlined above is urgently needed. Here, we assessed the composition, toxicity and repellent activities of cottonseed oil to A. guerreronis and its naturally occurring predator Typhlodromus ornatus Denmark &amp; Muma (Acari: Phytoseiidae). Our results revealed that the major compounds in cottonseed oil were linoleic and oleic acids, which have been shown to be bioactive against pests. Concentration-mortality bioassays revealed that A. guerreronis (LC50 = 0.65 μL/cm2) was more susceptible to cottonseed oil than its predator (LC50 = 5.11 μL/cm2). Similarly, as demonstrated for the conventional acaricides (i.e., abamectin, azadirachtin, espirodiclofen, and fenpyroximate), cottonseed oil was shown to repel A. guerreronis and its predator. Overall, our findings support the use of cottonseed oil as a desirable tool to be integrated in management programs aimed at controlling A. guerreronis.

Deltamethrin toxicity and impaired swimming behavior of two backswimmer species.

Backswimmers (Hemiptera: Heteroptera: Notonectidae) are insect predators in a wide variety of freshwater habitats. These insects are well known through their role as mosquito biocontrol agents, their ability to prey on immature fishes and frogs, and because they are often the first to colonize aquatic habitats. As a consequence, these predators may face intended or unintended insecticide exposures that may lead to death or to impairment of essential behaviors (e.g., swimming and position in the water column). The toxicity of deltamethrin (a type II pyrethroid insecticide stressor) and the swimming activity of the backswimmers Buenoa tarsalis and Martarega bentoi were evaluated. Concentration-mortality and survival bioassays were conducted with the insecticide, which were compared with controls without deltamethrin. Deltamethrin was 26-fold more toxic to B. tarsalis (median lethal concentration [LC50] = 4.0 ng a.i./L) than to M. bentoi (LC50 = 102.5 ng a.i./L). The pattern of occupation of B. tarsalis, but not of M. bentoi, in the water column was also disrupted, and B. tarsalis was forced to stay near the water surface longer with exposure to deltamethrin. Thus, based on the findings, B. tarsalis was less resilient to deltamethrin exposure compared with M. bentoi, and the efficacy of swimming-dependent processes might be negatively affected (e.g., prey catching, partner encounter, and antipredator behaviors) for B. tarsalis under deltamethrin exposure. Environ Toxicol Chem 2017;36:1235-1242. © 2016 SETAC.