Thirty-minute test to detect insecticide resistance under field conditions: the case of the Asian citrus psyllid.

BACKGROUND: Diaphorina citri Kuwayama is one of the most destructive citrus pests worldwide. It is controlled mainly through applications of conventional insecticides. Methodologies used to estimate resistance to insecticides do not correlate with field efficacy, and do not provide timely and reliable information to make decisions at a site where spraying is needed. The use of diagnostic doses with 30-min exposure is proposed for estimating the resistance of D. citri to imidacloprid, spinosad, malathion and chlorpyrifos at the orchard level. RESULTS: Under laboratory conditions, we estimated the lowest doses that caused 100% mortality within 30 min of exposure (diagnostic dose) in a susceptible D. citri colony. The diagnostic doses for imidacloprid, spinosad, malathion and chlorpyrifos were 7.4, 4.2, 1.0 and 5.5 mg a.i. L-1 , respectively. Under field conditions, we applied the diagnostic doses to D. citri feeding on Citrus aurantifolia Swingle at five localities in Michoacan state, Mexico (Nueva Italia, Santo Domingo, El Varal, Gambara and El Ceñidor). Additionally, the field efficacy of these insecticides against these populations was evaluated. A significant correlation between field efficacy and mortality was observed with the diagnostic doses for imidacloprid, malathion and chlorpyrifos (R2 ≥ 0.93). The correlation for spinosad could not be estimated because the mortality caused by the diagnostic dose and its field efficacy at all study sites was consistently >98%. CONCLUSIONS: Field efficacy and resistance were estimated based on the field diagnostic doses with 30-min exposure for all tested insecticides. Consequently, growers and pest management technicians can estimate the performance of the evaluated insecticides at the orchard level and before insecticide application. © 2023 Society of Chemical Industry.

In Vitro Insecticidal Effect of Commercial Fatty Acids, ß-Sitosterol, and Rutin against the Sugarcane Aphid, Melanaphis sacchari Zehntner (Hemiptera: Aphididae).

ABSTRACT: The sugarcane aphid, Melanaphis sacchari Zehntner (Hemiptera: Aphididae), is the main pest of sorghum, Sorghum bicolor L. Moench (Poaceae), in Mexico. To control this insect, farmers currently use synthetic chemical insecticides, which are toxic to humans and biodiversity. However, natural products are a promising potential source of safer alternative means to control different agricultural pests. The main objective of this study was to evaluate the insecticidal effect of contact by fumigation of pure molecules of four commercial fatty acids (palmitic, stearic, pentadecanoic, and linoleic acids), the phytosterol ß-sitosterol, and the flavonoid rutin. The results showed that fatty acids were the most effective against M. sacchari; the highest mortality rate (85%) was produced by linoleic acid and the mean lethal concentration was 1,181 ppm, followed by stearic and palmitic acids with 74 and 63% mortality, respectively, at a concentration of 2,500 ppm at 72 h. The positive control, imidacloprid, had 100% mortality in 24 h and the Tween 20, negative control, exhibited 4% mortality in 72 h. Our results show that commercial fatty acids are effective against adults of M. sacchari and can be considered an environmentally friendly alternative to the frequent use of synthetic chemical insecticides.

Antifungal Activity of Beauveria bassiana Endophyte against Botrytis cinerea in Two Solanaceae Crops.

Botrytis cinerea causes substantial losses in tomato and chili pepper crops worldwide. Endophytes have shown the potential for the biological control of diseases. The colonization ability of native endophyte strains of Beauveria bassiana and their antifungal effect against B. cinerea were evaluated in Solanaceae crops. Root drenching with B. bassiana was applied, and endophytic colonization capacity in roots, stems, and leaves was determined. The antagonistic activity was evaluated using in vitro dual culture and also plants by drenching the endophyte on the root and by pathogen inoculation in the leaves. Ten native strains were endophytes of tomato, and eight were endophytes of chili pepper. All strains showed significant in vitro antagonism against B. cinerea (30-36%). A high antifungal effect was observed, and strains RGM547 and RGM644 showed the lowest percentage of the surface affected by the pathogen. Native strains of B. bassiana colonized tomato and chili pepper tissues and provided important levels of antagonism against B. cinerea.

Susceptibilities of Geographic Populations of Helicoverpa zea (Lepidoptera: Noctuidae) in Mexico to Bt ∂-Endotoxins Cry1Ac and Cry2Ab: An 18-Yr Study.

An insect resistance monitoring program was developed for Mexico to accommodate the commercial introduction and stewardship of Bt cotton. Between 1998 and 2015, field-collected geographic populations of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) were evaluated against Cry1Ac and Cry2Ab proteins of Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) to establish baseline susceptibility data before the commercial use of Bollgard (Cry1Ac) and Bollgard II (Cry1Ac and Cry2Ab) cotton. An annual monitoring program was subsequently established in which a single diagnostic concentration of each Bt protein was used in a diet overlay bioassay. The diagnostic concentration represented the concentration where larvae, evaluated in baseline studies, were reduced in weight by ≥97% relative to untreated controls or failed to molt to third instar after 5 d. In the monitoring study, populations were tested against Cry1Ac from 1998 through 2015, and against Cry2Ab from 2002 through 2004 and again from 2007 through 2015. None of the Cry1Ac-exposed larvae tested during the 18-yr period reached the third larval instar after an exposure of 5 d, and weight reduction relative to untreated control larvae was uniform at about 98-99%. For the 12 yr of Cry2Ab monitoring, no larvae reached third instar, and weight reduction was uniform at >97% relative to controls. These results indicate that H. zea susceptibility to Cry1Ac and Cry2Ab has not changed during the period Bollgard and Bollgard II have been cultivated in Mexico.

[Fitness of Bemisia tabaci (Gennadius) B Biotype (Hemiptera: Aleyrodidae) populations with different levels of susceptibility to the thiametoxam insecticide]. / Aptitud biológica de poblaciones de Bemisia tabaci (Gennadius) Biotipo B (Hemiptera: Aleyrodidae) con diferente susceptibilidad al insecticida thiametoxam.

In two field-collected populations of de Bemisia tabaci (Gennadius) B biotype previously selected with the neonicotinoid insecticide thiamethoxam (NEO-R, NEO-N), and a population susceptible to insecticides (SUSC), the level of response to the insecticide thiametoxam, as well as the life and fertility tables were determined. At LC95, the NEO-R population showed a resistance ratio (RR95) value of 8.8-fold, an intrinsic rate of increase (r m) of 0.72. The fitness of the NEO-R and NEO-N populations in relation to the SUSC was 1.5 and 2.0, respectively. The RR95 value for NEO-N was 1.9-fold; it's r m value was 0.082, while in the SUSC population was 0.041. The developmental time of egg and adult were longer in NEO-R population, while the nymph and pupa lasted longer in the NEO-N and SUSC populations. The developmental time was different in the three NEO-R, NEO-N, and SUSC populations with 19.7 d (315.84 degree days or dd), 15.7 d (250.4 dd) and 18.5 d (296.6 d), respectively. The populations previously selected with thiamethoxam did not reproduce faster than their susceptible counterpart.

[Toxicity of spiromesifen to the developmental stages of Bactericera cockerelli (Sulc) (Hemiptera: Triozidae)]. / Toxicidad de spiromesifen en los estados biológicos de Bactericera cockerelli (Sulc) (Hemiptera: Triozidae).

Spiromesifen is an insecticide that inhibits the synthesis of lipids and, in Mexico, its use against the Tomato-Potato Psyllid, Bactericera cockerelli (Sulc), on chili pepper (Capsicum annum), tomato (Lycopersicon sculentum) and potato (Solanum tuberosum) began in 2005; however more information is needed to understand its toxicity on this insect pest. The aim of this research was to determine the toxicity of spiromesifen against each of the biological stages of tomato-potato psyllid, its effect on fertility and viability of eggs deposited by treated females, as well as the female preference to lay eggs on treated and non treated plants. The relative toxicity at 95% mortality (highest LC95 value /LC95 value of the respective biological stage) of spiromesifen in egg, nymph 1, nymph 2, nymph 3, nymph 4, and nymph 5 were 517.5; 31316.2; 2950.1; 315.6; 18.2 and 1-fold, respectively. There were no differences in the toxicity of spiromesifen between adult males and females. The number of laid eggs was reduced as the spiromesifen concentration used to treat female increased and egg hatch was reduced in all tested doses. In the "no choice" test, females deposited 38.6+/-2.01 eggs by leaf of non treated chili pepper type jalapeño, while in the treated with 360 mg L(-1) we observed 0.3+/-0.08 eggs by leaf. In the "choice" test, the oviposition decreased as the dose increased. There were no eggs on plants treated with 2400 mg L(-1) of spiromesifen.

Aptitud biológica de poblaciones de Bemisia tabaci (Gennadius) Biotipo B (Hemiptera: Aleyrodidae) con diferente susceptibilidad al insecticida thiametoxam / Fitness of Bemisia tabaci (Gennadius) B Biotype (Hemiptera: Aleyrodidae) populations with different levels of susceptibility to the thiametoxam insecticide

In two field-collected populations of de Bemisia tabaci (Gennadius) B biotype previously selected with the neonicotinoid insecticide thiamethoxam (NEO-R, NEO-N), and a population susceptible to insecticides (SUSC), the level of response to the insecticide thiametoxam, as well as the life and fertility tables were determined. At LC95, the NEO-R population showed a resistance ratio (RR95) value of 8.8-fold, an intrinsic rate of increase (r m) of 0.72. The fitness of the NEO-R and NEO-N populations in relation to the SUSC was 1.5 and 2.0, respectively. The RR95 value for NEO-N was 1.9-fold; it's r m value was 0.082, while in the SUSC population was 0.041. The developmental time of egg and adult were longer in NEO-R population, while the nymph and pupa lasted longer in the NEO-N and SUSC populations. The developmental time was different in the three NEO-R, NEO-N, and SUSC populations with 19.7 d (315.84 degree days or dd), 15.7 d (250.4 dd) and 18.5 d (296.6 d), respectively. The populations previously selected with thiamethoxam did not reproduce faster than their susceptible counterpart.

Toxicidad de spiromesifen en los estados biológicos de Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) / Toxicity of spiromesifen to the developmental stages of Bactericera cockerelli (Sulc) (Hemiptera: Triozidae)

Spiromesifen is an insecticide that inhibits the synthesis of lipids and, in Mexico, its use against the Tomato-Potato Psyllid, Bactericera cockerelli (Sulc), on chili pepper (Capsicum annum), tomato (Lycopersicon sculentum) and potato (Solanum tuberosum) began in 2005; however more information is needed to understand its toxicity on this insect pest. The aim of this research was to determine the toxicity of spiromesifen against each of the biological stages of tomato-potato psyllid, its effect on fertility and viability of eggs deposited by treated females, as well as the female preference to lay eggs on treated and non treated plants. The relative toxicity at 95 percent mortality (highest LC95 value /LC95 value of the respective biological stage) of spiromesifen in egg, nymph 1, nymph 2, nymph 3, nymph 4, and nymph 5 were 517.5; 31316.2; 2950.1; 315.6; 18.2 and 1-fold, respectively. There were no differences in the toxicity of spiromesifen between adult males and females. The number of laid eggs was reduced as the spiromesifen concentration used to treat female increased and egg hatch was reduced in all tested doses. In the "no choice" test, females deposited 38.6 ± 2.01 eggs by leaf of non treated chili pepper type jalapeño, while in the treated with 360 mg L-1 we observed 0.3 ± 0.08 eggs by leaf. In the "choice" test, the oviposition decreased as the dose increased. There were no eggs on plants treated with 2400 mg L-1 of spiromesifen.