General Insect Management 747
can be sampled readily and enough research has been conducted to estimate injury, commodity damage,
and insect growth rate. Furthermore, it requires that the lowest detectable amount of insects or injury
does not cause an economic loss. When an insect has a cryptic lifestyle (e.g., soil-dwelling, stalk borer),
or a single insect causes economic losses (e.g., disease vectors of humans and animals), a practical EIL
and AT cannot be calculated. Fortunately, sampling stink bugs generally is feasible, and diseases vec-
tored are limited in scope, so EILs and ATs are possible for many stink bug-host relationships (Hall and
Teetes 1982, Negrón and Riley 1987, Pantoja et al. 2000, Greene et al. 2001, Musser et al. 2011).
The concept of EIL and AT was introduced by Stern et al. (1959). Later a mathematical calculation
for EIL was developed by Pedigo et al. (1986). There is no general mathematical formula available for
the AT because it is impacted by scouting frequency, time between scouting and taking an action, time
between taking an action and getting results, the link between the insect stage sampled and the damaging
life stage, and the population growth rate of the insect.
16.3.1.5.2 Insecticide Modes of Action
Insecticides have been developed that kill insects in numerous ways. These various modes of action pro-
vide growers with a variety of tools that have varying levels of specificity, risks to humans, and environ-
mental risks. Each insecticide is categorized based on its mode of action (Insecticide Resistance Action
Committee 2016) so that users can choose a product that best fits their needs. A common recommenda-
tion is for users to rotate among several modes of action in order to prevent or delay the development of
resistance to the insecticides (Immaraju et al. 1990, Prabhaker et al. 1998). These insecticide modes of
action can be grouped into four broad categories, namely neuromuscular toxins, insect growth regula-
tors, cellular respiration disruptors, and midgut disrupters.
Neuromuscular toxins attack the nervous system or muscles of insects. These tend to be fast-acting
products that control a broad spectrum of insects. Unfortunately, many aspects of the insect nervous
system are similar to the human nervous system, so these products tend to be more dangerous to humans.
Early insecticides and the majority of insecticides used currently belong to this category. Widely used
classes of insecticides that work on the nervous system include the organophosphates, carbamates, pyre-
throids, neonicotinoids, and diamides. Each of these insecticide classes works on a specific nervous sys-
tem target (e.g., organophosphates inhibit acetylcholinesterase; pyrethroids lock axonic sodium channels
open), so rotation of products even within this broad category can reduce the development of insecticide
resistance.
Insect growth regulators impact growth and development, especially of immature insects. These insec-
ticides generally mimic or inhibit essential hormones involved in the molting process. They generally
have minimal human toxicity problems and are not lethal to adults of even the target species. Because
they kill by disrupting molting, the impact is only evident following a molt, so newly molted insects may
continue to live and feed for several days after application.
Cellular respiration disruptors affect the cellular respiration process, which shuts down normal
physiological functions of the insect. Most products in this small category interfere with mitochondrial
functions.
Midgut disruptors describe all Bacillus thuringiensis (Bt) products, both transgenic and conventional
types. These products require ingestion by the insect. The insecticide binds to the midgut, creating pores
that allow the contents of the midgut to mix with the hemolymph, thereby killing the insect (Gill et al.
1992). Bt commercialized products currently target numerous lepidopteran, dipteran, and coleopteran
pests, while having little to no impact on other insect orders or other non-target species. However, many
Bt toxins have been identified without knowing which species they control, so more diversity in insect
targets of Bt products is expected in the future.
16.3.1.5.3 Application Strategies
The decision about how to apply chemical controls should be made based on the target pest, the host, and
the environment. The first chemical control decision needs to be made before or at planting. Some soil-
dwelling insects (e.g., white grubs, wireworms) feed on the seed or roots of seedlings, but, because they
live below the soil surface, they cannot be controlled with foliar insecticide applications. Options include