April 2020 - 12

PLANT HEALTH
dr. bugs
BY RAYMOND A. CLOYD
Are XXpire and Altus Neonicotinoids?
Question: I have heard that XXpire is returning to the marketplace for use in
greenhouse production systems. However, I am curious; are XXpire and Altus
considered neonicotinoids?
Answer: You ask a very good question. Nonetheless, I think
we need to first step back and understand some background
information associated with XXpire and Altus before
answering your question. XXpire (Corteva Agriscience)
contains the active ingredients spinetoram and
sulfoxaflor. Sulfoxaflor is a sulfoximine-based insecticide
active on sucking insect pests of greenhouse production
systems, including aphids, mealybugs and whiteflies.
Altus (Bayer Environmental Science) contains the
active ingredient flupyradifurone. Flupyradifurone is a
butenolide-based insecticide active on the same sucking
insect pests as sulfoxaflor.
Now let's discuss mode of action. The Insecticide
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.
Resistance Action Committee (IRAC) designates
insecticides (and miticides) into specific classifications
and sub-groupings based on mode of action. The
current general mode of action for all IRAC 4
insecticides is as nicotinic acetylcholine receptor
(nAChR) competitive modulators. However, within the IRAC 4
classification there are five sub-groups: 4A, 4B, 4C, 4D and 4E.
Sub-groups are different classes of insecticides that have similar
modes of action but differ based on structure or interactions
with proteins or receptors on the target site. The neonicotinoids
(imidacloprid, dinotefuran, thiamethoxam, clothiandin and
acetamiprid) are in sub-group 4A, sulfoxaflor is in sub-group 4C,
and flupyradifurone is in sub-group 4D.
Therefore, XXpire and Altus are not technically considered
neonicotinoids. However, the question should not be whether XXpire
and Altus are neonicotinoids, but rather what are the modes of
action of XXpire and Altus, and are these insecticides harmful to
bees - honey bees and bumble bees?
MODE OF ACTION
Sulfoxaflor and flupyradifurone have the same mode of action as
the neonicotionids by functioning as an agonist (a substance that
acts like another substance in stimulating an action) on the insect
nicotinic acetylcholine receptors (nAChRs) by mimicking the natural
neurotransmitter. However, there may be chemical or molecular
structural differences, and/or metabolic differences among the
insecticides regarding biological interactions in insect pests. For
instance, the chemical structural differences between sulfoxaflor
and the neonicotinoids may result in distinct interactions associated
with binding on the target site (nAChRs). Flupyradifurone
supposedly acts differently than the neonicotinoids on the target
site (nAChR), and there may be differences in the chemical
structure between flupyradifurone and the neonicotinoids. However,
12 APRIL 2020 GPNMAG.COM
it is interesting to note that the metabolites (products of chemical
reactions that occur naturally within cells during metabolism)
of flupyradifurone include 6-chloronicotinic acid, which is also
a metabolic byproduct of many neonicotinoids. In general,
sulfoxaflor, flupyradifurone and the neonicotinoids are active on
the same target site (nAChR) in the insect central nervous system.
Therefore, these insecticides should not be used successively in
rotation programs to avoid cross-resistance (resistance based on
a single resistance mechanism conferring resistance to pesticides
in the same chemical class and/or having similar modes of action)
developing in insect pest populations.
BEE TOXICITY
First of all, let's consider the label information associated with
XXpire and Altus:
XXpire: this product is highly toxic to bees exposed through
contact during spraying and while spray droplets are still wet.
Toxicity is reduced when spray droplets are dry. This product
is toxic to bees exposed to treated foliage for up to three hours
following application. Do not apply this pesticide to blooming,
pollen-shedding or nectar-producing parts of plants if bees are
foraging on the plants during this time period. Risk to managed
bees and native pollinators from contact with pesticide sprays or
residues can be minimized by limiting applications to times when
managed bees and native pollinators are least active - two hours
prior to sunset or when the temperature is below 50° F at the site of
application.
Altus: this pesticide is toxic to adult bees in laboratory studies
via oral exposure; however, it is not toxic to bees through contact
exposure, and field studies conducted with this product have shown
no effects on honey bee colony development.
The results of studies vary regarding the direct and/or indirect
(sublethal) harmful effects of sulfoxaflor on bees (honey bees and
bumble bees) with some studies indicating harmful effects, such
as: negatively impacting reproduction of bumble bees, whereas
others suggest no harmful effects. However, in general, any harmful
effects are similar to those of the neonicotionids. There are also
conflicting results affiliated with studies on the direct and sublethal
toxic effects of flupyradifurone on bees. Nonetheless, studies show
that flupyradifurone displays similar effects on honey bees as the
neonicotinoids with sublethal effects on survival and behavior.
The bottom line is that neonicotinoids, sulfoxaflor and
flupyradifurone have very similar modes of action and bee toxicity.
Therefore, insecticides in the IRAC sub-groups 4A, 4C and 4D should
not be used successively in rotation programs and should not be
applied to plants that produce flowers attractive to bees.
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April 2020

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