What is biological insecticides?
Biological insecticides (or bioinsecticides) are a class of pesticides that use living organisms (such as bacteria, viruses, fungi, nematodes, and plant extracts) or their metabolites to control pests. They are generally effective against specific target pests and relatively safe for the environment and non-target organisms (such as bees, natural predators, and mammals). They are important tools in green agriculture and integrated pest management (IPM).
Most commonly, bacteria produce toxins that harm insects when ingested. Viruses and protozoa disrupt insect feeding, leading to starvation. Fungi control insects by growing on their surfaces, secreting enzymes that weaken the insect’s outer shell, then entering the insect’s body to continue growing and ultimately killing the infected pest. Finally, nematodes kill the target organism by entering the insect’s natural pores or by directly penetrating the insect’s cuticle. Most biocontrol agents work through one or more of the following modes of action: competition, parasitism, antimicrobial activity, and induced resistance.
What are the types of Biological insecticides?
1. Microbial insecticides
The active ingredients of these insecticides are microorganisms themselves or their metabolites. They are the most important and widely used type of biopesticide.
ⅠBacterial-Based bioinsecticides
A wide variety of commercially available bioinsecticides are based on the insect pathogen Bacillus turigensis. Bacillus turigensis is the most widely used and best-described biopesticide worldwide. This aerobic, Gram-positive bacterium belongs to the family Bacillaceae and is widely found in vegetative forms in soil, water, air, and plants. Bacillus insecticides rely on the activity of Cry proteins, which disrupt the insect midgut epithelium, leading to larval mortality. This class of insecticides accounts for over 90% of the microbial insecticide market and is primarily used in organic agriculture. Different Bacillus insecticides may contain different strains expressing different Cry genes. For example, insecticides derived from B. turigensis var kurstaki and var aizawai control lepidopteran pests, while insecticides based on B. turigensis var san diego or var tenebrionis control coleopteran pests.
ⅡFungal bioinsecticides
bioinsecticides based on entomopathogenic fungi have been used for decades. These parasites, acting as heavy parasites, invade their hosts through natural cuticle ruptures or by creating them using enzymes such as chitinases. Beauveria bassiana is one of the world’s best-known entomopathogenic fungi. It exhibits bioinsecticide activity against various whitefly species at all stages of their life cycle, particularly the larval stages (eggs and larvae), although the most sensitive stage is the N1 larvae. It also has some insecticide activity against aphids, thrips, and some caterpillars. The infection cycle in susceptible insects is particularly rapid. Initial symptoms appear 24 to 48 hours after contact. Spores penetrate the cuticle of the target insect, develop hyphae, and proliferate deeply within the insect. A mycelial mass forms 48 to 72 hours after contact, with maximum sporulation occurring 5 to 7 days later.
Metarhizium anisopliae, which acts in a similar manner to Beauveria bassiana, is commonly used to control subterranean pests and locusts.
ⅢVirus-Based bioinsecticides
Insect-pathogenic viruses are potentially important biocontrol agents. Most commercial bioinsecticides are based on viruses, including baculoviruses isolated from various insect orders. Infection with these viruses occurs primarily during feeding in the larvae, leading to the death of susceptible cells. Viruses that infect neighboring cells rapidly spread throughout the larvae, ultimately killing the host. Various commercial products based on insecticidal viruses are available worldwide.
2.Botanical insecticides
Substances extracted from plants with insecticidal activity.
ⅠAzadirachtin is an insect growth regulator extracted from the seeds of the neem tree. Azadirachtin is known to affect approximately 200 insect species, interfering with their feeding and inhibiting their ability to molt from pupae to adults.
ⅡPyrethrins is extracted from pyrethrum flowers, they rapidly knock down insects by acting on their nervous system. They readily decompose under light and leave low residues.
ⅢRotenone is extracted from the roots of the Derris plant, it is a broad-spectrum insecticide, but it is highly toxic to fish and should be used with caution.
ⅣOthers: Nicotine, matrine, etc.
3. Biochemical Pesticides
Naturally occurring substances that control pests but are not themselves living organisms.
ⅠInsect pheromones: Sex pheromones are most commonly used to disrupt insect mating. By releasing synthetic pheromones, male moths are confused, preventing them from finding females for mating, thereby reducing the next generation’s population. This is a highly targeted pest control method.
ⅡInsect Growth Regulators (IGRs): Synthetic substances that mimic natural hormones in insects, such as juvenile hormone analogs (which inhibit larval molting) and ecdysone analogs (which induce premature molting), disrupting normal growth and development and causing death.
What are advantages and disadvantages of Biological insecticides?
Advantages of bioinsecticides
ⅠEnvironmentally friendly: They are easily degradable, have low residues, and cause minimal pollution to soil and water sources.
ⅡTarget specific: They are generally effective only against specific pests and are safe for natural enemies (such as ladybugs and parasitic wasps) and pollinators (such as bees), thus contributing to the ecological balance of farmland.
ⅢSafe for humans and animals: They have minimal or no toxicity to mammals, making them safer for applicators and consumers.
ⅣResistant to developing resistance: With diverse mechanisms of action (stomach poison, contact poison, growth regulation, etc.), pests are unlikely to develop resistance. Even if resistance does develop, it is slower than with chemical pesticides.
ⅤSuitable for Integrated Pest Management (IPM): They are compatible with a variety of natural enemies and some chemical pesticides, making them an ideal choice for IPM systems.
Limitations of bioinsecticides
ⅠSlow onset: They typically take days or even weeks to show noticeable results, unlike the immediate effects of chemical pesticides.
ⅡPoor efficacy stability: Their effectiveness is significantly affected by environmental conditions (temperature, humidity, and ultraviolet light). For example, fungicides require high humidity, and direct sunlight can degrade many plant-based extracts.
ⅢThis high specificity is both an advantage and a disadvantage: if a mixed pest infestation occurs in a field, multiple bioinsecticides may need to be used in combination, increasing complexity.
ⅣStorage and shelf life: Live microbial preparations require strict storage conditions (such as refrigeration) and generally have a shorter shelf life than chemical pesticides.
ⅤRelatively high costs: High R&D and production costs result in a market price that is generally higher than that of traditional chemical pesticides.
Summary:Biological insecticides represent the future of agricultural pest control and are a crucial tool for achieving sustainable agricultural development. While they currently have some limitations, their effectiveness and stability are continuously improving with technological advancements. They cannot completely replace chemical pesticides, but when used in conjunction with chemical pesticides as part of an integrated pest management (IPM) strategy, they can minimize chemical pesticide use, delay the development of pesticide resistance, protect the ecological environment, and ensure food safety.