Samuel Pineda

Lethal and Sublethal Effects of Methoxyfenozide and Spinosad on Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract Susceptibility to methoxyfenozide ofSpodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) larvae was determined through exposure of neonate and fourth instars to dipped and sprayed pepper,Capsicum annum L., leaves. Methoxyfenozide and spinosad were tested against adults of this noctuid by oral, residual, and topical application. In larvae, we evaluated five (range, 0.001–10 mg active ingredient [AI]/liter) and six (range, 1–250 mg [AI]/liter) concentration levels by instars, respectively, by using two application methods at three different age leaf residues (0, 3, and 6 d after application). According to LC50 values, no significant differences were observed between the same age leaf residues of both application methods at 96 and 72 h after ingestion treatment on neonates and fourth instars, respectively. Nevertheless, toxicity of methoxyfenozide decreased significantly after time. For both application methods, the LC50 values of the first leaf residue (0 d after application) were significantly lower than those of 6-d-old residues. Furthermore, larval weight of fourth instars fed for 48 h with pepper,Capsicum annum L., leaves containing methoxyfenozide was significantly suppressed. Spinosad and methoxyfenozide reduced in a dose-dependent manner the fecundity and fertility ofS. littoralis adults when treated oral and residually. Likewise, when methoxyfenozide was administered orally in three different adult crosses, the fecundity was strongly affected, independently of the treated sex. We conclude that the combination of lethal and sublethal effects of methoxyfenozide and spinosad might exhibit significant effects on the population dynamics ofS. littolaris.

Monitoring of beet armyworm resistance to spinosad and methoxyfenozide in Mexico.

BACKGROUND Resistance to spinosad and methoxyfenozide has been studied in several insect pests, but there is a lack of information on Spodoptera exigua (Hübner) in Mexico. Therefore, evidence for the development of resistance in this pest to both compounds was examined. The effects of methoxyfenozide on reproductive parameters of S. exigua adults were also determined. RESULTS Third instars from a field population were exposed for 24 h to the LC(50) of spinosad or methoxyfenozide for over six generations (G(2)-G(7)). No significant reduction in susceptibility to either compound was detected for up to five generations. In G(7), LC(50) values for insects exposed to spinosad and methoxyfenozide were respectively 2.75-fold and 1.25-fold greater than for G(1) larvae. Oral treatment with methoxyfenozide reduced the fecundity and fertility of G(7) adults, confirming sublethal effects on reproduction. Finally, five populations (Se-La Floriza, Se-Lazareto, Se-Bachigualato, Se-Los Agustinos and Se-Villa de Arista) of S. exigua were collected from fields in three states of Mexico for resistance monitoring to spinosad and methoxyfenozide. With the exception of Se-Villa de Arista, the other populations showed significant resistance to spinosad, with resistance ratios between 16- and 37-fold, compared with a susceptible laboratory colony. In contrast, only one population (Se-Lazareto) showed significant resistance to methoxyfenozide (13-fold). CONCLUSION Resistance management programmes should be established, particularly in areas where S. exigua has developed resistance to spinosad.

Influence of Azadirachtin and Methoxyfenozide on Life Parameters of Spodoptera littoralis (Lepidoptera: Noctuidae)

ABSTRACT Effects on adult longevity, fecundity and fertility, as well as long-term effects on progeny were determined through oral exposure of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) adults to azadirachtin and methoxyfenozide. Both compounds reduced adult longevity by 2.3 d at the higher concentrations tested, but no significant differences were observed between sexes. Fecundity and fertility were significantly affected for both insecticides, although this effect was only dose-dependent for azadirachtin. The progeny from adults treated with azadirachtin or methoxyfenozide were only affected in percentage of pupation of eggs that successfully hatched, but no effects were observed in adult emergence of individuals that successfully pupated for either insecticide. In the second part of this study, each sex was exposed separately to methoxyfenozide by topical application or ingestion. Adult fecundity was more affected when moths were treated by ingestion than when treated topically, with a mean number eggs laid per female of 343 ± 89 and 932 ± 79, respectively. Finally, azadirachtin applied to pepper plants showed a significant oviposition deterrence activity on S. littoralis adults. However, when fecundity was scored for one additional day in females that had been previously exposed to pepper, Capsicum annum L., plants treated with this insecticide, the number of eggs laid per female did not differ significantly from that of controls. The effects of azadirachtin and methoxyfenozide on S. littoralis suggest changes in population dynamics of this pest in crops treated with these insecticides.

Toxicity and Pharmacokinetics of Spinosad and Methoxyfenozide to Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract The toxicity of spinosad and methoxyfenozide against neonates and fourth instars of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was tested under laboratory conditions. According to LC50 values, no significant differences were observed between spinosad (0.50 mg [AI]/kg diet) and methoxyfenozide (0.54 mg [AI] /kg diet) after 48 h of ingestion treatment on neonate larvae, based on the overlap of 95% CL. Similarly, on fourth instars, no significant differences were observed between LC50 (2.98 and 5.17 mg [AI]/kg diet for spinosad and methoxyfenozide, respectively, at 96 h after ingestion of artificial diet) and LD50 (4.74 and 2.68 μg [AI]/g larva for spinosad and methoxyfenozide, respectively, at 144 h after topical application). In addition, spinosad and methoxyfenozide significantly suppressed weight gain of neonates and fourth instars continuously fed with artificial diet containing the insecticides. The second part of this project was focused on the effects of methoxyfenozide on the reproduction of S. littoralis by determining the effect on oviposition in three different crosses and the pharmacokinetics pattern of (14C)-methoxyfenozide in the body tissues of female and male adults after topical application in their excrement and in the deposited eggs to test transport through the female and the male adult. Methoxyfenozide negatively affected the reproduction of adults regardless the treated sex, presumably because of its presence in the adult body, accumulation in the laid eggs, and slow excretion of the product. We conclude that spinosad and methoxyfenozide represent an important choice to be used in integrated pest management where S. littoralis is a major pest.

Toxicity and sublethal effects of methoxyfenozide on Spodoptera exigua (Lepidoptera: Noctuidae).

ABSTRACT The toxicity and sublethal effects of methoxyfenozide were evaluated in third instars of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), that fed on contaminated semisynthetic diet. The LC50 value was estimated at 0.23 mg of active ingredient (AI)/kg diet (range, 95% CI: 0.17–0.37) at 264 h after treatment. The effects on development, survival, and reproduction were observed in third instars of this pest that survived exposure to an LC25 concentration of methoxyfenozide. The larvae from the insecticide treatment exhibited lower pupal weights, an increase in both larval and pupal developmental times and a higher frequency of malformations of the wings in adults than untreated larvae. Adults from the methoxyfenozide treatment did not show reduced fecundity (mean cumulative number of eggs laid per female), but fertility as measured by the percentage of eggs hatched (fertility) was significantly reduced compared with untreated control insects. No significant effects were observed on pupal sex ratio. We concluded that the lethal and sublethal effects of methoxyfenozide are likely to have a significant impact on S. exigua populations on treated crops.

Pathogenicity of Two Entomopathogenic Fungi on Trialeurodes vaporariorum and Field Evaluation of a Paecilomyces fumosoroseus Isolate

Entomopatogenic fungi are a promising alternative for the control of agricultural pests. We evaluated the pathogenicity of three isolates of Paecilomyces fumosoroseus (Wize) Brown and Smith (Pf1, Pf2, and Pf3) and six isolates of Lecanicillium (= Verticillium) lecanii (Zimmermann) Zare and Gams (VI1, VI2, VI3, VI4, VI5, and VI10) on eggs, second, third, and fourth nymphal instars of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Three of the nine isolates (Pf1, VI3, and VI5) produced 11–26% infections of eggs, while the remaining isolates had no significant effect (Pf3 and VI10) or were unable (Pf2, VI1, VI2, and VI4) to infect this developmental stage. Pf1, Pf2, and Pf3 caused homogeneous pathogenicity in all nymphal instars tested, while L. lecanii isolates showed high variability. Pf1, Pf2, and Pf3 were usually the most pathogenic, but their activity correlated inversely with increasing nymphal instars. The pathogenicity (number of living nymphs recovered from treated plots) of Pf2 on T. vaporariorum nymphs was evaluated on zucchini squash plants in two experimental trials. Survival of whitefly nymphs decreased by 19 and 28% after the first and second fungal applications, respectively, in one trial, and by 62 and 71% in the other trial. Based on these results, we concluded that the use of fungal preparations based on the Pf2 isolate could be feasible for controlling T. vaporariorum.

Toxicity and Residual Activity of Insecticides against Tamarixia triozae (Hymenoptera: Eulophidae), a Parasitoid of Bactericera cockerelli (Hemiptera: Triozidae)

ABSTRACT Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is one of the most economically important pests of potato, tomato, and peppers in Central America, Mexico, the United States, and New Zealand. Its control is based on the use of insecticides; however, recently, the potential of the eulophid parasitoid Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) for population regulation has been studied. Because T. triozae is likely to be exposed to insecticides on crops, the objective of this study was to explore the compatibility of eight insecticides with this parasitoid. The toxicity and residual activity (persistence) of spirotetramat, spiromesifen, beta-cyfluthrin, pymetrozine, azadirachtin, imidacloprid, abamectin, and spinosad against T. triozae adults were assessed using a method based on the residual contact activity of each insecticide on tomato leaf discs collected from treated plants growing under greenhouse conditions. All eight insecticides were toxic to T. triozae. Following the classification of the International Organization of Biological Control, the most toxic were abamectin and spinosad, which could be placed in toxicity categories 3 and 4, respectively. The least toxic were azadirachtin, pymetrozine, spirotetramat, spiromesifen, imidacloprid, and beta-cyfluthrin, which could be placed in toxicity category 2. In terms of persistence, by day 5, 6, 9, 11, 13, 24, and 41 after application, spirotetramat, azadirachtin, spiromesifen, pymetrozine, imidacloprid, beta-cyfluthrin, abamectin, and spinosad could be considered harmless, that is, placed in toxicity category 1 (<25% mortality of adults). The toxicity and residual activity of some of these insecticides allow them to be considered within integrated pest management programs that include T. triozae.

Long‐term foliar persistence and efficacy of spinosad against beet armyworm under greenhouse conditions

BACKGROUND The immediate lethality caused by spinosad has been widely studied on Spodoptera exigua (Hübner). However, long-term effects can also provide valuable information on insecticide toxic action. Here, the persistence of spinosad on Capsicum annuum L. foliage and the lethal and sublethal effects of greenhouse-aged foliar residues of this insecticide on third instars of S. exigua are reported. RESULTS Foliage was collected at 0, 3, 5, 10, 20, 30, 40 and 50 days after application, and spinosad residues were measured. Residues decreased over time according to first-order kinetics. The average rate constant and half-life of disappearance were 4.44 × 10(-3) and 156 days and 5.80 × 10(-3) and 120 days for 60 and 120 mg L(-1) respectively. Larval mortality gradually decreased, corresponding to the residues, but was still appreciable (35 and 65% for 60 and 120 mg L(-1) respectively) when the larvae were fed with foliage collected 50 days after treatment. Subsequently, pupal development was reduced and varied between 20 and 60% and between 21 and 41% for 60 and 120 mg L(-1) , respectively, in all ages of leaf residues that were bioassayed. At all time points, the consumption rate by the larvae was reduced between 62 and 84% for both concentrations that were bioassayed. CONCLUSION It is concluded that, under the present greenhouse conditions, the degradation of spinosad was slower than that reported by other authors in the field, and, because of that, its residues could cause lethal and sublethal effects to S. exigua larvae.

Insecticide resistance of adults and nymphs of Asian citrus psyllid populations from Apatzingán Valley, Mexico

BACKGROUND Control of the Asian citrus psyllid Diaphorina citri Kuwayama, the most important pest of citrus worldwide, is based on the use of insecticides, though unsatisfactory results have recently been reported. In this study, insecticide resistance of D. citri to three insecticides (bifenthrin, malathion, and chlorpyrifos) was examined. RESULTS Three populations (designated Dci-CParácuaro, Dci-El Junco, and Dci-Antúnez) of both adults and fourth-instar D. citri individuals were collected in 2014 at two different times and on one occasion, respectively, from three locations (Crucero de Parácuaro, El Junco, and Antúnez). These locations represent the major commercial Mexican lemon production areas in the Apatzingán Valley in the state of Michoacán, Mexico. The three populations of D. citri adults and fourth-instar nymphs at the different collection times showed low levels of resistance (≤7-fold) to bifenthrin, but were very resistant to malathion (≤345- and ≤432-fold for adults and fourth instars, respectively) and chlorpyrifos (≤2435- and ≤1424-fold for adults and fourth instars, respectively). CONCLUSION Resistance levels to the tested insecticides were highly variable but homogeneous among seasons and localities. Resistance management programmes that include crop sanitation, use of biological and cultural control practices, and rotation of insecticide classes should be established, particularly in areas where D. citri has developed resistance to malathion and chlorpyrifos.

Behavior of Tamarixia triozae Females (Hymenoptera: Eulophidae) Attacking Bactericera cockerelli (Hemiptera: Triozidae) and Effects of Three Pesticides on This Parasitoid

ABSTRACT The parasitism and host feeding behavior of Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) females on Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) fourth instars that have infested tomato (Lycopersicon esculentum Miller) leaflets are described and quantified. Females took approximately 31.14±4.39 min to search for their first suitable host. The recognition and handling times for oviposition were 2.66±0.18 and 4.26±0.39 min, respectively. T. triozae parasitized 4.66±0.61 nymphs in a period of 6 h. The parasitoid explored and probed its host by walking along the margins of its body while antennating and repeatedly introducing the ovipositor beneath the nymph. The handling times before and during host feeding were 8.42±0.67 and 8.29±0.60 min, respectively. T. triozae females consumed 1.00±0.00 B. cockerelli nymph after parasitizing 3.3±0.48 nymphs. EPA—a refined soybean oil—imidacloprid, and abamectin caused between ∼70 and 100% T. triozae adult mortality after a 48-h contact treatment with fresh pesticide residue and a 47–91% decrease (abamectin > imidacloprid > EPA) in adult emergence when parasitized B. cockerelli fourth instars were directly sprayed. These data suggest that the use of these insecticides in combination with T. triozae in integrated pest management programs should be carefully evaluated.