Biochemical Biopesticides: Insect Growth Regulators

Biopesticide Insect Growth Regulators (IGRs) have a unique mode of action separate from most chemical insecticides. Generally speaking, these products prevent insects from reaching a reproductive stage, thereby reducing the expansion of pest populations. The direct impact of IGRs on target pests combined with the preservation of beneficial insects and pollinators aids growers in maximizing yield and product quality.

IGRs can be divided into two broad categories; i.e. those that disrupt the hormonal regulation of insect metamorphosis, and those that disrupt the synthesis of chitin, a principal component of insect exoskeletons . Agricultural applications currently focus on the first category of compounds, products which are also known as “hormone mimics.”

Azadirachtin is one of the most widely used botanical insect growth regulators. Because of its structural resemblance to the natural insect molting hormone ecdysone, azadirachtin interrupts molting, metamorphosis, and development of the female reproductive system. Immature insects exposed to azadirachtin (mainly by ingestion) may molt prematurely or die before they can complete a properly timed molt. Those insects that survive a treatment are likely to develop into a deformed adult incapable of feeding, dispersing, or reproducing.

Since beneficial insects, predators, and pollinators do not feed directly on the treated foliage, biopesticide insect growth regulators are considered “soft” on beneficial insects such as honeybees, lady bugs, green lacewings, and the parasitic wasps.

Due to their unique mode of action, biochemical insect growth regulators have played an important role in integrated pest management systems and as an effective resistance management tool.  A good example is the use of azadirachtin IGR in aphid population management programs for lettuce crops in the Salinas Valley, Calfornia.  Due to restrictions placed on certain crop protection products, the lettuce industry has relied on the use of contact and systematic control measures – some with overlapping modes of action – which creates concern for pesticide resistance. Integrated use of azadirachtin provides control by impacting the larvae and nymphs of multiple aphid species, breaking the life cycle before they become reproducing adults.

Another azadirachtin success story is its use for pear psylla control on pears in the Pacific Northwest Region of the US, where growers integrate traditional control products, azadirachtin, and kaolin clay for a effective pest management with significantly reduced use of harmful chemical insecticides.