Time and mortality curves (LT50) of Brazilian populations of
Coffee leafminer Leucoptera coffeella is an important pest on coffee. The continued use of chemicals can result in loss of efficacy and selection of leafminer-resistant populations. We aimed to identify L. coffeella populations resistant to old and new neurotoxic insecticides in regions of Brazil. We collected seven populations of L. coffeella in Brazil. Low levels of resistance were observed for the insecticides chlorantraniliprole (1.02-3.23 times), abamectin (1.19-4.80 times), and deltamethrin (1.05-5.35 times). High resistance levels were observed for profenofos (65.3-522 times) and chlorpyrifos (4.53-18.63 times). We conclude that Brazilian L. coffeella populations showed greater resistance to organophosphate insecticides. Furthermore, resistance may be associated with the distance between the coffee-producing regions.
- Coffea spp
- lethal time
The coffee leafminer
The first documented case of resistance was in 1914, in San Jose Scale (
Lepidopteran species such as
Among the insecticides used, most are neurotoxins, and it is this group that presents the most problems of insect resistance . These neurotoxic insecticides (e.g., organophosphates and pyrethroids) cause rapid death of susceptible insects, and abamectin, neonicotinoids, and diamides are slower in causing death of insects .
It is therefore possible to detect resistance to a particular active ingredient by comparing the time of death of each population to different neurotoxic insecticides. Similar experiments have been done with other insects, such as the mosquito
There are two studies focusing on the detection of insecticide resistance among populations of
2. Materials and methods
2.1. Insect populations
This study was conducted at the Laboratory of Integrated Pests Management at Universidade Federal de Viçosa, Rio Paranaíba Campus (UFV-CRP). We selected six municipalities with coffee cultivation of the species
The leaves collected in each region were transported to the laboratory in separate plastic bags for visual selection of mines that did not present any harm (e.g., open or with signs of parasitism/predation). Selected mined leaves were combined for insect rearing in a greenhouse (20 × 10 m). These leaves were placed in vials with water (25 mL) inside wooden cages covered with organza. The larvae were fed seedlings coffee of Catuaí cultivar grown in a greenhouse without insecticide application. Only larvae with at least one generation in the laboratory were used in bioassays to prevent the expression of insecticide tolerance due to differing environmental conditions at the different sampling sites (i.e., differences without any genetic basis).
Six neurotoxic insecticides were selected for bioassays of
|Abamectin||Rio Paranaíba-MG||13.29 (11.29–15.34)||40||1.74||2.87 (3)||0.59|
|Abaeté dos Mendes-MG||14.70 (12.59–16.53)||40||1.92||6.95 (3)||0.07|
|Carmo do Paranaíba-MG||36.75 (33.63–40.97)||40||4.80||4.05 (3)||0.26|
|Santa Teresa-ES||9.11 (6.03–11.52)||40||1.19||2.89 (3)||0.59|
|Guaranhuns-PE||17.85 (15.87–19.71)||40||2.33||4.97 (3)||0.17|
|Franca-SP||12.41 (10.99–15.12)||40||1.62||3.42 (3)||1.12|
|Guaraciaba-MG||7.65 (6.85–10.11)||40||1.00||5.63 (3)||3.11|
|Chlorpyrifos||Rio Paranaíba-MG||8.16 (7.02–9.20)||40||8.08||7.35 (4)||0.12|
|Abaeté dos Mendes-MG||17.18 (15.68–18.75)||40||17.01||9.07 (4)||0.06|
|Carmo do Paranaíba-MG||16.39 (15.12–17.76)||40||16.23||1.66 (3)||0.65|
|Santa Teresa-ES||4.58 (3.62–5.54)||40||4.53||7.56 (5)||0.18|
|Guaranhuns-PE||8.59 (6.70–10.21)||40||8.50||2.39 (3)||0.50|
|Franca-SP||18.82 (17.54–20.15)||40||18.63||8.20 (4)||0.08|
|Guaraciaba-MG||1.01 (0.35–2.07)||40||1.00||6.32 (7)||0.06|
|Chlorantraniliprole||Rio Paranaíba-MG||27.70 (24.70–31.56)||40||1.98||3.66 (3)||0.30|
|Abaeté dos Mendes-MG||26.30 (22.15–34.79)||40||1.88||1.57 (2)||0.54|
|Carmo do Paranaíba-MG Santa Teresa-ES||14.01 (11.87–16.47)||40||1.00||7.51 (5)||0.18|
|Santa Teresa-ES||31.53 (28.44–35.74)||40||2.25||5.50 (3)||0.14|
|Guaranhuns-PE||18.82 (17.54–20.15)||40||3.23||8.20 (4)||0.08|
|Franca-SP||14.28 (11.00–18.23)||40||1.02||6.30 (5)||1.22|
|Guaraciaba-MG||8.59 (6.70–10.21)||40||1.88||2.39 (3)||0.50|
|Deltamethrin||Rio Paranaíba-MG||31.12 (27.59–36.20)||40||5.35||4.96 (4)||0.17|
|Abaeté dos Mendes-MG||25.73 (23.34–28.56)||40||4.42||3.83 (3)||0.28|
|Carmo do Paranaíba-MG||28.18 (24.46–34.29)||40||4.84||2.22 (3)||0.53|
|Santa Teresa-ES||5.82 (4.23–7.65)||40||1.00||5.99 (4)||0.07|
|Guaranhuns-PE||20.38 (17.53–23.23)||40||3.50||6.04 (3)||0.11|
|Franca-SP||18.82 (17.54–20.15)||40||3.23||8.20 (4)||0.08|
|Guaraciaba-MG||6.11 (5.03–7.84)||40||1.05||5.81 (4)||0.06|
|Profenofos||Rio Paranaíba-MG||15.66 (13.96–17.17)||40||522||0.85 (5)||0.66|
|Abaeté dos Mendes-MG||12.25 (11.10–13.19)||40||408||1.35 (6)||0.51|
|Carmo do Paranaíba-MG||6.96 (4.28–9.00)||40||232||3.85 (5)||0.28|
|Santa Teresa-ES||1.96 (0.08–3.00)||40||65.3||3.71 (3)||2.32|
|Guaranhuns-PE||10.96 (8.50–11.00)||40||365||1.36 (4)||0.44|
|Franca-SP||12.96 (8.24–14.53)||40||432||4.12 (3)||0.21|
|Guaraciaba-MG||0.03 (0.01–0.50)||40||1.00||1.58 (3)||0.23|
|Thiamethoxam||Rio Paranaíba-MG||37.29 (33.32–43.21)||40||4.41||2.54 (3)||0.53|
|Abaeté dos Mendes-MG||23.10 (21.11–25.27)||40||2.73||0.43 (3)||0.93|
|Carmo do Paranaíba-MG||89.93 (61.70–180.00)||40||10.61||6.54 (4)||0.16|
|Santa Teresa-ES||10.49 (9.13–11.78)||40||1.24||8.65 (4)||0.07|
|Guaranhuns-PE||13.57 (12.07–14.87)||40||1.61||7.69 (3)||0.06|
|Franca-SP||8.45 (7.07–10.95)||40||1.00||5.66 (3)||1.05|
|Guaraciaba-MG||9.36 (7.01–10.34)||40||1.11||6.71 (3)||0.06|
The registered label rates of the respective active ingredients in Brazil were 0.18 mg mL-1 (0.026 mg a.i. mL-1) for abamectin, 0.072 mg mL-1 and 0.078 mg a.i. mL-1 for chlorantraniliprole, 0.05 mg mL-1 (4.800 mg a.i. mL-1) for chlorpyrifos, 0.032 mg mL-1 (0.013 mg a.i. mL-1) for deltamethrin, 0.4 mg mL-1 (1.100 mg a.i. mL-1) for profenofos, and 0.024 mg mL-1 (2.000 mg a.i. mL-1) for thiamethoxam.
2.3. Time-mortality bioassay
For time-mortality analysis, circular discs (diameter 90 mm) of filter paper were dipped into the insecticide solutions diluted in distilled water, using the recommended doses to control
Preliminary tests using only discs soaked in water were carried out to observe caterpillar mortality over a 48-h period. This was necessary to estimate the maximum evaluation time after bioassay assembly that causes 20% lower mortality in the control . Thus, to have a mortality range from 0% to 100%, evaluations were made at 2, 6, 12, 16, 24, 32 and 48 h (treatments) after bioassay assembly. The time intervals were assessed in independent experimental units, to avoid pseudoreplicates. We considered insects dead when they did not move after being touched with the fine-tipped brush.
2.4. Spatial dependence of insecticide resistance
To determine the spatial dependence of
3. Results and discussion
Resistance to neurotoxic insecticides varied generally among the different populations of
On the other hand, intermediate resistance was observed for thiamethoxam (1.11-10.61 times) and chlorpyrifos (4.53-18.63 times), while resistance was high for profenofos (65.3-522 times) (Table 1). Higher levels of organophosphate resistance were observed in Minas Gerais (Abaeté dos Mendes, Rio Paranaíba and Carmo do Paranaíba), Pernambuco (Guaranhuns), and São Paulo (Franca).
The RT50 values are supported by the LT50 values, which were variable among populations and insecticides. The population from Carmo do Paranaíba-MG was noteworthy as it took 89.93 h for 50% of the population to die after contact with the insecticide thiamethoxam. The organophosphate and pyrethroid insecticides had lower lethal times. Chlorantraniliprole showed lower LT50 of 8.59 h.
Two canonical axes were significant among the five canonical axes identified, showing linear associations between LT50 of the insecticides with the geographical regions of the population origins of
The opposite relationship was observed for assistance with the chlorpyrifos insecticide on the third and fourth axes. On the fifth and sixth axes, a positive relationship was observed between the profenofos insecticide and the standard deviation. It is important to highlight that the new insecticide chlorantraniliprole did not contribute to the resistance of populations (Table 2). Graphs of this analysis done with the first two axes explained 92% of the total variance of the data to show the grouping between locations (Table 2 and Figure 2).
The weight of organophosphate (profenofos and chlorpyrifos) and pyrethroid (deltamethrin) insecticides on the first two axes enhanced the resistance process since they are among the main groups with examples of insect resistance (quotation). Two grouping patterns were observed, with one group for the populations of
|68; 181||54; 181||46; 181||32; 181||20; 181||16; 181|
The semivariogram models related to the LT50 values of
Our study reported high variations in the resistance ratio (RT50) of the organophosphates profenofos (522 times) and chlorpyrifos (19 times) compared to the susceptible population of
This shows that this group of insecticides is extremely important in managing resistance because of its intense use, with this group being highly toxic and presenting higher neurotoxic action . Many studies on resistance to the organophosphate insecticide group showed high variation in the mortality of the resistant population compared to other lepidopteran populations [20,21]. Extensive insecticide use in coffee crops and high death speed are among the main factors of resistance . Fragoso et al.  observed up to 22 applications of organophosphate insecticides, detecting high levels of resistance when larvae were kept exposed to the discriminating concentration. These concentrations were higher than those tested for profenofos and chlorpyrifos in our study.
On the other hand, chlorantraniliprole, abamectin, and deltamethrin insecticides showed low levels of RT50 variation. The result with the chlorantraniliprole insecticide was as expected since this insecticide has only recently been commercialized [23-25] and has a highly efficient molecule since low doses of this insecticide (31.5 g a.i. ha-1) cause high mortality to
Selectivity is an important factor in managing resistance in pest insects . Many studies with basic lines of susceptibility have been done with chlorantraniliprole insecticide and Lepidoptera, and the observations are that populations show susceptibility with low variation in mortality [28,29]. The insecticide abamectin is not considered old and has been effective in controlling this pest insect, with no flaws detected in its control of
Insects usually have a resistance mechanism that confers nerve insensitivity, known as knockdown resistance (Kdr), as first reported in
The insecticide thiamethoxam has been frequently used and can be applied as a spray or via the soil . There are no studies of lepidopteran resistance to this insecticide. Control failures were observed depending on the time of application, however, for example  observed effectiveness of 4.1%, 50.6%, 62.1%, and 69.0%.
The grouping of populations from Rio Paranaíba, Carmo do Paranaíba, and Abaeté (Group I) and Santa Teresa with Guaraciaba (Group II), coupled with the significant response of the effect of distance on the LT50 of the chlorpyrifos, profenofos, and deltamethrin insecticides, showed that resistance was affected by the collection distance of these populations since more closely connected populations had similar resistance responses.
Studies have shown a strong relationship between collection distance and resistance patterns [44,10,45,12]. All of these studies showed significant association of resistance with distance, and nearby populations tended to show more similar responses, as is the case for
We conclude that Brazilian populations of
The funding and fellowships provided by the following Brazilian agencies were greatly appreciated: CAPES Foundation from the Brazilian Ministry of Education, National Council for Scientific and Tecnological Development (CNPq), and Minas Gerais State Foundation for Research Aid (FAPEMIG).