January 2024 - 14

DR. BUGS
In general, esterases detoxify insecticides
in the chemical classes, organophosphate
and pyrethroid, whereas glutathione
S-transferases detoxify organophosphate
insecticides. Insect pests that do not
possess these metabolic detoxifying
enzymes are more susceptible to
insecticides. Expression of these
metabolic detoxifying enzymes may be
induced when insect pests are exposed
to plant allelochemicals when feeding
on plants, which can decrease the
toxicity of insecticides, resulting in
fewer individuals being killed.
Insect pests exposed to
high concentrations of
plant allelochemicals
develop resistance
to insecticides more
rapidly. Furthermore,
resistance to
insecticides may
occur faster or in a
shorter time period
than resistance to plant
allelochemicals.
Insect pests with piercingsucking
mouthparts - such as
aphids - may already have low
levels of metabolic detoxifying enzymes
due to feeding on a wide range of different
horticultural plants. This could increase the exposure of
aphids to different plant allelochemicals, thus leading
to an increase in insecticide resistance. A consequence
of insect pests with inherent metabolic detoxifying
enzymes is that higher rates of insecticides may be
required to manage populations. In addition, the plant
fed upon by insect pests may influence the effectiveness
of insecticides. For example, sucking insect pests feed
within the vascular tissues [i.e., phloem (food-conducting
tissues) and/or xylem (water-conducting tissues)], which
may have lower concentrations of plant allelochemicals
compared to the leaf tissue (leaf parenchyma cells).
Therefore, sucking insect pests develop resistance at a
slower rate than chewing insect pests because of exposure
to lower concentrations of plant allelochemicals.
Plants produce a multitude of allelochemicals, which
Insecticide applications may not be
effective against insect pests previously
exposed to plant allelochemicals.
Aphids may already possess
metabolic detoxifying enzymes
because they feed on many different
horticultural plants.
detoxify or metabolize both the plant
allelochemicals and insecticides.
However, the selection pressure
associated with plant allelochemicals
may differ from that of insecticides based
on the feeding duration of the insect pest.
Generalist insect pests have evolved
mechanisms to detoxify a diverse array of plant
allelochemicals. As such, generalist insect pests may have
a greater propensity than specialist insect pests to detoxify
plant allelochemicals due to the presence of multiple
metabolic detoxifying enzymes. These same enzymes also
allow generalist insect pests to develop resistance to a
multitude of insecticides, even those with different modes
of action. Therefore, the metabolic detoxifying enzymes that
allow insect pests to overcome plant allelochemicals may
predispose insect pests to develop insecticide resistance.
Moreover, generalist insect pests feeding on many
different plant types may develop resistance to a wide range
and classes of insecticides than specialist insect pests due
to having a more diverse array of metabolic detoxifying
enzymes. Finally, insect pests that feed on a wide range of
plants are more likely to develop resistance to a broader
spectrum of insecticides due to greater exposure to
insecticide applications.
serve as defensive compounds to mitigate attacks from
insect pests. Consequently, insect pests exposed to
different plant allelochemicals may be less susceptible to
insecticides because the metabolic detoxifying enzymes can
14
JANUARY 2024 GPNMAG.COM
Raymond A. Cloyd is professor and Extension specialist in
horticultural entomology/plant protection at Kansas State
University. He can be reached at rcloyd@ksu.edu.
http://www.GPNMAG.COM
January 2024

Table of Contents for the Digital Edition of January 2024
