Reduced Risk of Resistance with Botanical Insecticides

Among the many benefits of the utilization of botanical insecticides versus synthetic pesticide compounds, one of the most important is the decreased chance of the development of insecticide resistance.  The overall economic impact of insecticide resistance in pests is estimated to be $1.5 billion annually in the USA alone (1).  And as we know, the price of insect resistance is not isolated to one operation, as neighboring nurseries, greenhouses, farms, etc. will also be affected, so growers constantly take pest resistance into consideration not only from a production efficiency perspective, but also a stewardship perspective.

Of course, pesticide and MOA rotation still needs to be practiced, just as with any pesticide.  However, there are unique characteristics of botanically-derived compounds that can help to further reduce the risk of resistance when used in IPM protocols and combined with rotation best practices.

Multiple Modes of Action (MOAs)

Some botanically-derived insecticide compounds naturally utilize multiple modes of action for insect knock-down and/or kill.  One great example is Azadirachtin which is derived from the Neem plant.  Azadirachtin (an active ingredient in products like Azera® Pro and Azera® Gardening), acts as both a feeding deterrent/antifeedant and repellant, as well as an insect growth regulator and sterilant.  This means Azadirachtin essentially gives your plants three modes of defense against insect pests:

Antifeedant:

Even at low concentrations, Azadirachtin acts as a feeding deterrent, protecting your plants from the damage caused by insects feeding on plant material:

Antifeedant chart showing efficacy against several pests.

Insect Growth Regulator:

Azadirachtin is structurally similar to the insect hormone ecdysone and inhibits the synthesis and release of ecdysone in over 400 species of susceptible insects.  This ecdysone disruption, along with degenerative changes in the endocrine glands caused by the compound, inhibits the insects from being able to molt.  This causes insects to die when transitioning into the next life stage or instar (insect stage between molts).

Normal:

Diagram showing normal molting in a lep.

Azadirachtin IGR Effect:

Diagram showing normal molting being disrupted by Azadirachtin.

Sterilant/Oviposition Inhibitor:

Azadirachtin also acts as a sterilant and prevents the production of future generations both through the anti-molting effect which disrupts the insect’s life cycle, as well as acts as an oviposition inhibitor.

Less Chemical Uniformity

Another way in which botanical insecticides can help growers reduce their risk of developing insecticide resistance is due to the more complex and various nature of naturally-occurring compounds.  Synthetic insecticides are based on very uniform chemical compounds.  Nature is less precise than a lab, and there is natural variation in the compounds that make up many botanical insecticides.

For example, Azadirachtin is technically not designated as a single compound, but a complex combination of related substances and compounds.  Another great example, Pyrethrum is a naturally-occurring insecticide derived from certain species of the Chrysanthemum family.  Pyrethrum is the active ingredient in many MGK botanical insecticides, including PyGanic, Azera, and EverGreen, and is well-known to have excellent and fast-acting knock-down and kill via Sodium Channel Modulator MOA.  Rather than being one specific compound, Pyrethrum is based on six distinct Pyrethrin Esters:

Diagram showing molecular diagram of the six pyrethrin esters.

It is easy to get confused regarding the terminology around Pyrethrum, so I find that this graphic helps:

PYRETHRUM = PLANT or extract PYRETHRINS = 6 active esters PYRETHRIN = a specific pyrethrin ester PYRETHROIDS = synthetic compounds modeled on the molecular structure  of a pyrethrin ester.

Unlike synthetic pyrethroids, the naturally derived Pyrethrum active ingredient is produced by plants. Therefore, there is natural variation in the number and combination of the six Pyrethrin esters that are present in any particular batch of extract.  This complexity and natural variation in chemical compound composition (both in Azadirachtin and Pyrethrum) are less likely to allow for the formation of resistance in the pest population.  However, the six pyrethrin esters certainly aren’t immune to resistance development. Remember to rotate pyrethrum with products based on different modes of action. Pyrethrins and pyrethroids are classified as group 3A on the Insecticide Resistance Action Committee (IRAC) http://www.irac-online.org/modes-of-action/

Combining Forces

A great way to maximize both of these benefits (Multiple Modes of Action and Less Chemical Uniformity), is to combine forces.  This is what MGK has done in the formulation of Azera Pro for professional plant production and Azera Gardening for home garden use.  Azera combines the benefits of the OMRI-Listed power of PyGanic (Pyrethrum concentrate) with its flushing effect and rapid knockdown and kill, with the longer-term and more diverse modes of action of Azadirachtin.  This provides the “One-Two Punch” that helps ensure maximum benefit of this botanical duo.

 

It is worth repeating that the use of botanically-derived insecticides will not replace or reduce the need for an insecticide rotation program.  Please consult an IPM professional for pest management advice.