Abstract
The introduction of an agricultural pest species into a new environment is a potential threat to agroecosystems of the invaded area. The phytosanitary concern is even greater if the introduced pest’s phenotype expresses traits that will impair the management of that species. The invasive tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is one such species and the characterization of the insecticide resistance prevailing in the area of origin is important to guide management efforts in new areas of introduction. The spinosad is one the main insecticides currently used in Brazil for control of the tomato borer; Brazil is the likely source of the introduction of the tomato borer into Europe. For this reason, spinosad resistance in Brazilian populations of this species was characterized. Spinosad resistance has been reported in Brazilian field populations of this pest species, and one resistant population that was used in this study was subjected to an additional seven generations of selection for spinosad resistance reaching levels over 180,000-fold. Inheritance studies indicated that spinosad resistance is monogenic, incompletely recessive and autosomal with high heritability (h 2 = 0.71). Spinosad resistance was unstable without selection pressure with a negative rate of change in the resistance level ( = −0.51) indicating an associated adaptive cost. Esterases and cytochrome P450-dependent monooxygenases titration decreased with spinosad selection, indicating that these detoxification enzymes are not the underlying resistance mechanism. Furthermore, the cross-resistance spectrum was restricted to the insecticide spinetoram, another spinosyn, suggesting that altered target site may be the mechanism involved. Therefore, the suspension of spinosyn use against the tomato borer would be a useful component in spinosad resistance management for this species. Spinosad use against this species in introduced areas should be carefully monitored to prevent rapid selection of high levels of resistance and the potential for its spread to new areas.
Highlights
Invasive agricultural pest species are widely recognized as a major threat to agroecosystems and agricultural production [1,2,3]
After reaching a plateau in the selection for spinosad resistance, the selection was interrupted in a line of selected insects exhibiting high spinosad resistance (.100,000-fold based on standard-susceptible strain) and such high resistance levels quickly eroded with a negative rate of change in subsequent generations without selection (RC = 2 1.06)
In countries managing invasive species and maintaining records of insecticide resistance development, insecticide use against the tomato borer can be described as waves of use of different groups
Summary
Invasive agricultural pest species are widely recognized as a major threat to agroecosystems and agricultural production [1,2,3]. The invasive species, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), the tomato borer or tomato leafminer ( tomato pinworm), is one such species It is of South American origin but was introduced into Europe as early as 2006. Problems with insecticide resistance in the tomato borer were soon detected in the late 1990’s and early 2000’s in Chile, Brazil and Argentina for the insecticides initially used against this species, including organophosphates, pyrethroids, abamectin and cartap [12,13,14,15,16,17] This resistance led to subsequent registration and large-scale use of new insecticides, in Brazil, including insect growth regulators, indoxacarb, chlorfenapyr, spinosyns, and diamides [10,18,19]. Produced tomatoes imposed additional restrictions and challenges for tomato borer control, culminating in the use of bioinsecticides, such as the spinosyn spinosad and PLOS ONE | www.plosone.org
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