Diaphorina citri Kuwayama (Hemiptera: Liviidae) is the most severe pest of citrus worldwide, and it has a high capacity to develop insecticide resistance. We estimated the intraplot variation of resistance to imidacloprid in adults collected from an orchard (8 ha) of Persian lemon, Citrus latifolia Tan., in Martínez de la Torre, Veracruz, Mexico. We divided the orchard into eight sections of similar size. Adults were sampled from each section to assess their response in the F1. We conducted two field samplings: November 2020 and May 2021. The relative response (RR50) at the median lethal mortality (LC50) level in adults collected in the first sampling varied from 518× to 16,701×. Adults collected from Sections 2 and 5 exhibited the highest LC50 values. In the second sampling, adults with the highest LC50 values were collected from Sections 3, 5, and 6. The range of intraorchard variation at the LC50 level (RR50) ranged from 635× to 6,626×. The RR95 values could be estimated in two sections of the first sampling: 7,421× (Section 7) and 58,958× (Section 8). For the remainder of the intraorchard sections in both samplings, the maximum concentration of imidacloprid that could be prepared was 100,000 mg/L, which caused a level of mortality that reached ≤87.9%. The range of variation at the LC50 among sections (FRR50) was low: 1 to 32.17× in the first sampling and 1 to 10.43× in the second. The resistance detected to imidacloprid is the highest recorded worldwide for D. citri.

The Asian citrus psyllid, Diaphorina citri (Kuwayama) (Hemiptera: Liviidae), is a severe pest of citrus orchards worldwide. Its control is based mainly on the use of conventional insecticides, and resistance to many of those compounds is widespread. Phenotypic bioassays to detect resistance compare the response of a field-collected population with a laboratory-reared population that is susceptible to insecticides. This comparison usually does not involve a susceptible field-collected counterpart since its existence is currently rare. We found an isolated field population of D. citri living on a wild host, orange jasmine (Murraya paniculata [L.] Jack). Considering its lifetime fly capacity, gene flow with any insecticide-treated population was nonexistent or negligible. Thus, we determined the response in fourth-instar nymphs and unsexed 2- to 5-d-old adults in bioassays of commercial formulations of the commonly used insecticides chlorpyrifos, malathion, imidacloprid, and spinosad. In the bioassays, insects were placed on leaf discs previously immersed for 10 s in the respective insecticide concentrations. For adults, the lowest concentration–mortality response was with chlorpyrifos (lethal concentration 50 [LC50] of 0.72 mg L-1 and lethal concentration 95 [LC95] of 1.02 mg L-1). The highest toxicity response was with malathion (LC95 of 0.05 mg L-1). The highest toxicity response with fourth-instar nymphs was observed with spinosad (LC50 of 0.007, LC95 of 0.021 mg L-1). The estimated LC50 and LC95 values for chlorpyrifos, malathion, and spinosad were lower than those documented worldwide for these insecticides in susceptible populations of D. citri.

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.