progresses, potentially worsening sublethal responses to pesticide exposure
[82, 83]. In combination, the acute and chronic (sublethal) effects of pyrethroid
pesticides are reshaping aquatic ecosystems, altering the makeup of communities
and likely reducing biodiversity as less sensitive species and taxa are favored to
thrive and survive.
4 Resistance to Pyrethroid Pesticides
Toxic levels of chemicals such as pyrethroids in the environment leave organisms
with few options: move, die, or acclimate. To date, pesticide resistance has been
described in more than 500 arthropod species (https://www.pesticideresistance.org/,
[84]). Measurable evolved resistance to a new pesticide class is considered a
certainty within 10 years, and resistance has even been observed within the span
of a single year [85]. If the selective force is strong enough to cause mortality or other
fitness (survival, growth, and reproduction) costs, adaptation can occur at the
population level in response to pyrethroid presence. The distinction between acclimation and adaptation is important in the discussion of decreased chemical sensitivity, largely because these two processes occur by different mechanisms that carry
with them different implications for affected populations. Physiological acclimation
refers to any coping mechanism that is governed by physiological processes that are
nonheritable. These mechanisms can include upregulation of detoxifying or sequestering enzymes and are characterized by an increased tolerance that is temporary
based on environmental conditions – when the stressor is removed, the tolerance
disappears over time. Adaptation refers to any heritable, genetically based tolerance
mechanism [86], such as the rise in frequency of a mutation conferring pyrethroid
target site insensitivity. Adaptive changes have the potential to be permanent and to
cause long lasting changes in populations [87]. The terms tolerance and resistance
have been used interchangeably in the literature to describe decreased chemical
sensitivity based on acclimation and/or adaptation. For clarity, we define tolerance
as a decreased sensitivity that is acclimatory or temporary in nature, occurring at the
organismal level, while resistance is a permanent change in sensitivity, conferred
through an adaptive mechanism (Fig. 3). Further we focus specifically on adaptive
responses to pyrethroid presence in the environment, and to be conservative, we
refer to decreased sensitivity caused by any mechanism (known or unknown) other
than an adaptive change as tolerance.
In general, acclimation and adaptation are sufficient to describe many ways that
the animals or populations respond to environmental conditions. Even in cases
where the phenotype of the offspring is determined by the genotype or environment
provided by the mother (maternal effects) [88], our understanding of individual or
population responses to the environment holds. Maternal effects caused by RNA or
protein transfer to the egg will fade in subsequent generations when the environment
of the mother is no longer relevant [89], qualifying these effects as a specific
subgroup of acclimation. Epigenetics can be broadly defined as the study of
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K. M. Major and S. M. Brander
[82, 83]. In combination, the acute and chronic (sublethal) effects of pyrethroid
pesticides are reshaping aquatic ecosystems, altering the makeup of communities
and likely reducing biodiversity as less sensitive species and taxa are favored to
thrive and survive.
4 Resistance to Pyrethroid Pesticides
Toxic levels of chemicals such as pyrethroids in the environment leave organisms
with few options: move, die, or acclimate. To date, pesticide resistance has been
described in more than 500 arthropod species (https://www.pesticideresistance.org/,
[84]). Measurable evolved resistance to a new pesticide class is considered a
certainty within 10 years, and resistance has even been observed within the span
of a single year [85]. If the selective force is strong enough to cause mortality or other
fitness (survival, growth, and reproduction) costs, adaptation can occur at the
population level in response to pyrethroid presence. The distinction between acclimation and adaptation is important in the discussion of decreased chemical sensitivity, largely because these two processes occur by different mechanisms that carry
with them different implications for affected populations. Physiological acclimation
refers to any coping mechanism that is governed by physiological processes that are
nonheritable. These mechanisms can include upregulation of detoxifying or sequestering enzymes and are characterized by an increased tolerance that is temporary
based on environmental conditions – when the stressor is removed, the tolerance
disappears over time. Adaptation refers to any heritable, genetically based tolerance
mechanism [86], such as the rise in frequency of a mutation conferring pyrethroid
target site insensitivity. Adaptive changes have the potential to be permanent and to
cause long lasting changes in populations [87]. The terms tolerance and resistance
have been used interchangeably in the literature to describe decreased chemical
sensitivity based on acclimation and/or adaptation. For clarity, we define tolerance
as a decreased sensitivity that is acclimatory or temporary in nature, occurring at the
organismal level, while resistance is a permanent change in sensitivity, conferred
through an adaptive mechanism (Fig. 3). Further we focus specifically on adaptive
responses to pyrethroid presence in the environment, and to be conservative, we
refer to decreased sensitivity caused by any mechanism (known or unknown) other
than an adaptive change as tolerance.
In general, acclimation and adaptation are sufficient to describe many ways that
the animals or populations respond to environmental conditions. Even in cases
where the phenotype of the offspring is determined by the genotype or environment
provided by the mother (maternal effects) [88], our understanding of individual or
population responses to the environment holds. Maternal effects caused by RNA or
protein transfer to the egg will fade in subsequent generations when the environment
of the mother is no longer relevant [89], qualifying these effects as a specific
subgroup of acclimation. Epigenetics can be broadly defined as the study of
116
K. M. Major and S. M. Brander