Behavior-Modifying Chemicals in the Insect World
Semiochemicals are chemical substances that insects use to communicate with each other and influence their behavior. They are used as non-conventional chemical control methods, as they do not target killing insects, but modify their behavior and decrease their damaging effects.
Insects receive those chemicals from their antennae. They are very specific in their effect. A chemical can have dual effects on different insects depending on the insect species that receive it! They can be classified into two main types: pheromones and allelochemicals.
- Pheromones: Pheromones are chemical signals released by insects that affect the behavior or physiology of other individuals of the same species ( intraspecific communication). They differ from hormones in that pheromones are secreted outside the body eliciting certain behavior, while hormones are secreted within the body to control physiological processes.
- Those chemicals are produced commercially and applied at a specific dose/ rate for the pest management process.
- The insect receives those chemical messages in the desired dose for a specific behavior, in case their concentration is increased or changed, the behavior might change. Even this situation can deliver the desired management to pest populations.
- They can be further categorized into different subtypes depending on the induced behaviors:
a. Sex Pheromones: These pheromones are released by one sex to attract the other sex for mating. Female insects often release specific pheromones that help them attract males. Scientists exert great effort during the identification process of these pheromones as they are very highly specific in their actions.
To manage certain pest populations, you have to use their specific pheromone!
So, their use is valuable when dealing with valuable crops or plants or even when used in constructions where the incidence of insect infestation is not accepted at all.
An example of this mate-attractive behavior can be seen in female bark beetles. The female when resting on the tree, releases the sex pheromone to attract males. Males recover the odor of both the female and the tree itself to fly towards it. Surprisingly, when males arrive there, they produce another pheromone to prevent the coming of more males to their tree!
Females also get this message and stop releasing their pheromones!
What interesting chemicals are produced in this scenario?
b. Aggregation Pheromones: Aggregation pheromones are emitted by insects to attract others of the same species to a specific location. This behavior is often observed in social insects like ants, bees, and termites, where the pheromones help in forming and maintaining colonies.
Usually the target hero’s food or reproduction site.
c. Alarm Pheromones: Alarm pheromones are released by insects when they are threatened or injured. These pheromones can signal danger to other individuals of the same species, triggering defensive behaviors or escape responses. The remains of the sting of a honeybee left
Its victim releases an alarm pheromone that attracts more bees to attack, so, be careful if you are near someone who was attacked as you may feel his suffering.
They are volatile and don’t persist otherwise the whole colony will be alert! Their concentration elicits different behavior; low concentration induces attraction in some insects. High concentration may lead to a digging behavior in others.
D. Trail Pheromones: Trail pheromones are used by social insects to mark paths between food sources and their nests. They help other members of the colony to locate and follow the trail to the food source could be a continuous line of secretions or discrete spots. They are long-lasting and do not evaporate quickly.
e. Aphrodisiac’s pheromones:
They are a kind of sexual attractants that lead to the copulation process during mating.
Some moths have a scent gland under their wings that secretes this pheromone. Removing this gland was found to be the reason for the inability of the male to mate.
f. Epideictic pheromones:
They are called spacing pheromones as they cause a dispersal away from a crowded place, especially food sources.
Any of these pheromones can be used in attract and kill programs, sampling, and detection of insect populations, or mating disruption processes.
The other group of behavior-modifying chemicals are Allelochemicals.
2. Allelochemicals: Allelochemicals are chemical signals that insects use to interact with other species (inter-specific interaction), including members of different insect species, predators, or prey. These chemicals can have various roles in insect behavior depending on the individual having benefits.
a. Kairomones: Kairomones are allelochemicals that benefit the receiver (usually a different species) while being produced by another organism. For example, some insects release kairomones to attract predators or parasitoids that prey on their herbivorous pests.
b. Allomones: Allomones are allelochemicals that benefit the sender by deterring or repelling other organisms. These chemicals can be used by insects to defend themselves against predators or to repel competing species.
Sometimes plants produce defensive chemicals for protection against pests.
Also, insect predators produce chemicals that attract their prey.
c. Synomones: Synomones are allelochemicals that benefit both the sender and the receiver. They can be released by plants to attract beneficial insects for pollination or to repel herbivores.
Another interesting example is found in cockroaches.
They harbor symbiotic protozoa within their gut. These protozoa help the cockroaches in digesting cellulose and the cockroach molting hormone helps the protozoa in its life cycle.
Semiochemicals play crucial roles in insect behavior, including mate attraction, territory marking, foraging, alarm responses, and defense mechanisms. Understanding these chemical signals is important for pest management, insect ecology, and developing strategies for sustainable agriculture.
While semiochemicals have proven to be effective tools in insect pest management, there are some potential drawbacks and limitations to consider:
1. Specificity: Semiochemicals are often species-specific or have limited effectiveness across different pest populations. The effectiveness of a semiochemical may vary among different geographic regions or strains of the same pest species. Therefore, it is essential to identify and develop semiochemical formulations that are specific to the target pest population.
2. Variability: Semiochemicals can be influenced by various environmental factors, such as temperature, humidity, and wind direction. These factors can affect the release, dispersion, and detection of semiochemicals, making their effectiveness inconsistent under different environmental conditions.
3. Development Costs: The development and synthesis of synthetic semiochemicals can be costly and time-consuming. Extensive research and testing are required to identify, isolate, and synthesize effective semiochemical compounds. Additionally, the production and formulation of semiochemical-based products can be expensive, limiting their accessibility to some farmers or pest management practitioners.
4. Integration with Other Control Strategies: Semiochemicals are most effective when integrated with other pest management strategies. While they can be used as part of an integrated pest management (IPM) approach, combining semiochemicals with other control methods, such as biological control or insecticides, may be necessary for optimal pest management outcomes.
5. Resistance Development: Although less common compared to insecticide resistance, there is a potential for pests to develop resistance to semiochemicals. Continuous and exclusive use of semiochemicals as a control measure may exert selective pressure on pest populations, leading to the development of resistance over time. To mitigate this risk, it is important to use semiochemicals in combination with other control measures and rotate or alternate semiochemical formulations.
6. Practical Implementation: The successful implementation of semiochemical-based pest management strategies often requires careful monitoring, precise timing, and strategic placement of traps or dispensers. This can be labor-intensive and may require specialized training and expertise. Therefore, the adoption of semiochemical-based approaches may pose practical challenges for some farmers or pest control operators.
Despite these limitations, semiochemicals remain valuable tools in integrated pest management programs. Their use, when combined with other tactics, can contribute to sustainable and environmentally friendly pest control strategies. Ongoing research and development efforts are focused on addressing these limitations and improving the practicality and effectiveness of semiochemical applications in pest management.
Alnaqaa for environmental services -Ras Al Khaimah- United Arab Emirates is continuously offering pest management services within the framework of the guidance of her scientific consultants using behavior—modifying chemicals together with other natural non-conventional chemical insecticides
