Short- and long-term effects of commercial formulations of imidacloprid, spirotetramat, and mixtures of these active ingredients on pupae of Diaeretiella rapae (Hymenoptera: Braconidae) and its progeny.

BACKGROUND: Compatibility studies of insecticides and natural enemies usually focus on short-term lethal effects, without considering the long-term sublethal effects (including progeny). Even less-explored are the effects of commercial insecticides formulated with more than one active product. Short- and long-term lethal and sublethal effects were studied for the first time on the progeny of commercial formulations of spirotetramat, imidacloprid and a commercial mixture of these active ingredients on pupae of Diaeretiella rapae (M'ntosh) (Hymenoptera: Braconidae), an endoparasitoid of aphids considered to be a potential biological control agent. Insecticides were exposed topically on aphid mummies in which the parasitoid was in the pupal stage. RESULTS: Imidacloprid reduced adult emergence by more than 30% and prolonged intra-host development time with respect to control from half the maximum recommended field dose (MFRD). Spirotetramat and commercial mixture only showed significant effects on these endpoints at doses above the MFRD. The tested formulations did not affect adult longevity, sex ratio, and percentage of parasitism in the exposed generation. At low concentrations the active ingredients in the commercial mixture behave synergistically, whereas at medium and high concentrations they behave antagonistically. Considering the 10% lethal dose (LD10), imidacloprid showed the highest hazard coefficient, whereas the commercial mixture was more hazardous when considering the LD50 and LD90. The commercial mixture and imidacloprid induced higher adult emergence and altered the sex ratio in the progeny. CONCLUSIONS: The following order of toxicity on D. rapae can be established: imidacloprid > commercial mixture > spirotetramat. Joint use of this species with imidacloprid and commercial mixture should be avoided in integrated pest management programs. © 2024 Society of Chemical Industry.

Selectivity assessment of two biorational insecticides, azadirachtin and pyriproxyfen, in comparison to a neonicotinoid, acetamiprid, on pupae and adults of a Neotropical strain Eretmocerus mundus Mercet.

Assessment of the susceptibility of natural enemies of pests to selective pesticides is relevant for a sustainable agriculture with low impact on the environment. The aim of this study was to assess the toxicity of two biorational insecticides, azadirachtin and pyriproxyfen in comparison to a neonicotinoid insecticide, acetamiprid, on pupae and adults of a Neotropical strain of Eretmocerus mundus. Adult emergence and survival were evaluated as lethal effects whereas the sublethal effects were assessed through the reproductive capacity, sex ratio, and longevity of the surviving first progeny. Adult emergence from treated pupae was reduced by all three insecticides, but azadirachtin at its maximum field recommended concentration (MFRC) proved the most toxic insecticide. The survival probability of emerged adults was reduced by the three insecticides below than 50% from 2 to 5 days after the adult emergence. Malformations in nonemerged adults from treated pupal hosts were observed at the MFRC of all three insecticides. Sublethal effects on survivors from pupal treatment could be evaluated at only the lowest azadirachtin concentration. At that concentration, though azadirachtin did not affect the reproductive capacity of females, the sex ratio and the longevity of the first progeny were disrupted. The survival of parasitoid adults after adult exposure was reduced by all three insecticides, pyriproxyfen at the MFRC being the most toxic. All insecticides at their half of MFRCs induced sublethal effects in the survivors' adults, with pyriproxyfen being the most harmful to the reproductive capacity of females. In conclusion, both biorational insecticides were toxic to E. mundus.

Side effects of spirotetramat on pupae and adults of a Neotropical strain of Eretmocerus mundus (Hymenoptera: Aphelinidae): Effects on the life parameters and demography.

The negative impact of conventional pesticides on the environment is already extensively discussed worldwide. Although the use of chemical agents for controlling agricultural pests remains as first-line strategy for pest control, novel biorational active insecticides, such as spirotetramat, have appeared in the pesticide market during recent years in Argentina. The aim of this study was to assess the toxicity of spirotetramat on two developmental stages of a Neotropical strain of Eretmocerus mundus, with the conventional insecticide cypermethrin as a positive control, and to determine spirotetramat's side effects on parasitoid demographic parameters. Lethal effects of both insecticides on pupae and adults were evaluated by adult emergency and survival, respectively; whereas sublethal effects on both development stages were assessed by adult longevity, reproduction capacity, sex ratio, and longevity of the first progeny. Spirotetramat proved less harmful than cypermethrin at both developmental stages studied, corroborating once more the high toxicity of this pyrethroid to natural enemies. Although spirotetramat did not affect the emergence and reproductive capacity of adults surviving pupal exposure, the longevity of the first progeny was reduced as was adult survival and longevity after exposure to residues. Spirotetramat also reduced all demographic parameters in the population evaluation. This work is the first report of spirotetramat toxicity at the population level and demonstrates the need to assess the total effect of pesticides on natural enemies.

Toxicity assessment of four insecticides with different modes of action on pupae and adults of Eriopis connexa (Coleoptera: Coccinellidae), a relevant predator of the Neotropical Region.

Pesticides can be toxic to nontarget organisms including the natural enemies of agricultural pests, thus reducing the biodiversity of agroecosystems. The lethal and sublethal effects of four insecticides with different modes of action-pyriproxyfen, teflubenzuron, acetamiprid, and cypermethrin-were evaluated on pupae and adults of Eriopis connexa, an effective predator in horticultural crops. Pupal survival was reduced by pyriproxyfen (26 %) and cypermethrin (41 %). Malformations in adults emerged from treated pupae were observed after acetamiprid (82.7 and 100 % for 100 and 200 mg a.i./l, respectively), pyriproxyfen (48.6 %), and cypermethrin (13.3 %) treatments. A longer mean oviposition time was also observed in adults emerged from pupae treated with cypermethrin. Moreover, the latter insecticide as well as teflubenzuron did not reduce reproductive parameters, whereas females emerged from pyriproxyfen-treated pupae were not be able to lay eggs even when females showed large abdomens. Upon exposure of adults, survival was reduced to approximately 90 % by acetamiprid, but no reduction occurred with pyriproxyfen, teflubenzuron, or cypermethrin though the fecundity at fifth oviposition time of the female survivors was reduced. Pyriproxyfen decreased the hatching at all the oviposition times tested, whereas fertility was reduced in the fourth and fifth ovipositions by teflubenzuron and in the first and third ovipositions by cypermethrin. In conclusion, all four insecticides tested exhibited lethal or sublethal effects, or both, on E. connexa. The neurotoxic insecticides were more harmful than the insect-growth regulators, and pupae were more susceptible than adults. The toxicity of insecticides on the conservation of predators in agroecosystems of the Neotropical Region is discussed.

Impact of the neonicotinoid acetamiprid on immature stages of the predator Eriopis connexa (Coleoptera: Coccinellidae).

Eriopis connexa is a native coccinelid predator in the Neotropical Region. In Argentina it is commonly found associated to sucking pests in several crops and among them aphids and whiteflies. These pests are usually controlled with newly developed systemic insecticides, such as the neonicotinoids. However, the compatibility between selective pesticides and natural enemies is required before incorporating them in integrated pest management (IPM) packages. Within this frame, the objective of this study was to evaluate the side effect of various concentrations/doses of one commonly used neonicotinoid in vegetal crops, acetamiprid, on immature stages of E. connexa by dipping or topical exposure for eggs and larvae, respectively. Acetamiprid reduced egg hatching from 34 to 100 %. Moreover, the embryogenesis was disrupted by insecticide at early embryo stage at all tested concentrations. Second larval instar was more susceptible to acetamiprid than the fourth one and this susceptibility was positively related with the tested concentrations. On the other hand, the survival reduction at larval stage reached 100 % from 20 mg a.i./L (10 % of maximum field concentration). Besides, the reproduction of the females developed from topical bioassays on fourth instar larvae was strongly affected, with reduction in fecundity and fertility from 22 to 44 % and from 37 to 45 %, respectively. Overall the results showed a high toxicity of acetamiprid on immature stages of E. connexa, demonstrating that this broadly used insecticide could reduce biocontrol services provided by this predator and could also likely disturb IPM programs.

Long-term effects of methoxyfenozide on the adult reproductive processes and longevity of Spodoptera exigua (Lepidoptera: Noctuidae).

The long-term effects of methoxyfenozide on the longevity and reproductive processes of beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), adults were assessed after exposure by ingestion. Methoxyfenozide significantly reduced adult male longevity compared with females by 1.1 and 1.5 d at 75 and 150 mg (AI)/liter, respectively. Fecundity decreased by >60% with both concentrations at 72 and 96 h after treatment, but at 48 h, no significant effect was observed. The carbohydrate, protein, and lipid content in the eggs were determined as representatives of the biochemical effects of methoxyfenozide associated with the disruption of reproductive processes. The content of carbohydrates in the eggs laid 48 h at treatment was similar to that of controls, but it increased by approximately 1.5 and 2-fold in eggs laid after 72 and 96 h, respectively, compared with controls (15 microg per egg). Protein content was reduced approximately 2.5 and approximately 3-fold for each treatment concentration, respectively, compared with the controls (25 and 23 microg per egg for 75 and 150 mg [AI]/liter, respectively) in eggs collected 72 and 96 h after treatment. Lipid content significantly decreased by approximately 1.6-fold in both treatment concentrations in eggs collected at 48 and 96 h after treatment compared with the controls (24 and 21 microg per egg for 48 and 96, respectively), but it was similar to controls (approximately 19 microg per egg) at 72 h (approximately 15 microg per egg) for both concentrations. The biochemical effects of methoxyfenozide on S. exigua egg formation detected in this work are consistent with the reduction in fertility observed, as reported previously.

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

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.

Influence of azadirachtin and methoxyfenozide on life parameters of Spodoptera littoralis (Lepidoptera: Noctuidae).

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.

Susceptibility of Chrysoperla externa eggs (Neuroptera: Chrisopidae) to conventional and biorational insecticides.

Chrysoperla externa (Hagen) is a generalist predator in agroecosystems. We assessed the effect of cypermethrin, endosulfan, methoxyfenozide, and spinosad on immature development time, survivorship, sex ratio, fecundity, and fertility on this organism in laboratory toxicity tests. Effects on second-generation organisms were also studied. Exposures were realized by dipping

Lethal and sublethal effects of methoxyfenozide and spinosad on Spodoptera littoralis (Lepidoptera: Noctuidae).

Susceptibility to methoxyfenozide of Spodoptera 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 of S. 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 methoxy-fenozide and spinosad might exhibit significant effects on the population dynamics of S. littolaris.

Effects of two biorational insecticides, spinosad and methoxyfenozide, on Spodoptera littoralis (Lepidoptera: Noctuidae) under laboratory conditions.

The toxicity of two biorational insecticides, spinosad (Tracer) and methoxyfenozide (RH-2485), was tested against eggs, larvae, and pupae of the noctuid Spodoptera littoralis (Boisduval). In the first experiment, filter paper circles containing egg masses of two different age classes, young (<24 h old) and old (24-48 h old), were dipped in different concentrations of each insecticide diluted in either water or acetone. No ovicidal activity was recorded when insecticides were diluted in water. In contrast, when insecticides were diluted in acetone, both egg age classes generally showed a concentration-dependent response for both compounds. Mortality of larvae that hatched from both egg age classes was significantly increased, compared with control larvae, at all concentrations of both insecticides when diluted in water or acetone alike. The prevalence of mortality was similar with each insecticide. In the second experiment, third instars of S. littoralis were fed semisynthetic diet containing different concentrations of both insecticides. According to LC50 values, no significant differences were observed between spinosad (2.11 mg [AI]/kg diet) and methoxyfenozide (3.98 mg [AI]/kg diet) after 48 h of treatment, based on the overlap of 95% CL. Toxic effects on the mortality of pupae, adult emergence, and the prevalence of deformed adults after topical application on young pupae also were examined. Only methoxyfenozide caused pupal mortality and deformed adults. Our results suggest that spinosad and methoxyfenozide are potentially potent compounds for control of S. littoralis.

Toxicity and pharmacokinetics of insect growth regulators and other novel insecticides on pupae of Hyposoter didmator (Hymenoptera: Ichneumonidae), a parasitoid of early larval instars of lepidopteran pests.

Susceptibility of the lepidopteran parasitoid Hyposoter didymator (Thunberg) to seven modern insecticides, azadirachtin, diflubenzuron, halofenozide, methoxyfenozide, pyriproxyfen, tebufenozide, and spinosad, was tested in the laboratory. Pupae were exposed to different doses of each compound by direct topical application. At the field recommended doses, methoxyfenozide and tebufenozide had no effect on H. didymator. Halofenozide had a low effect on both adult emergence and adult survival but the progeny size and parasitism capacity were not affected. Diflubenzuron was moderately toxic to the parasitoid, while azadirachtin, pyriproxyfen and spinosad were very toxic, affecting all its life parameters. In the pyriproxyfen and spinosad treatments, no progeny was obtained. As a second approach of this study, we determined the rate of penetration through the pupal cocoon and absorption in the parasitoid body as pharmacokinetic parameters important for toxicity. Most of the radioactivity was retained in the silken cocoon, indicating a low accumulation in the parasitoid body. Among all compounds tested, diflubenzuron exhibited the highest absorption in the parasitoid body, followed by pyriproxyfen. For halofenozide, methoxyfenozide and tebufenozide, low absorption (<2%) was found. In addition, we tested for the presence of molting hormone receptors in Hyposoter tissues using a monoclonal antibody 9B9. Our data suggest that the use of diflubenzuron azadirachtin, pyriproxyfen, halofenozide, and spinosad in combination with H. didymator in integrated pest management (IPM) programs should be carefully evaluated. Methoxyfenozide and tebufenozide could be considered safe for this parasitoid.