Insect pest monitoring

To control insect pests, it is necessary to first determine the damage situation and create an optimal control plan, considering the environmental conditions and characteristics. Insect pest monitoring is the first basic step for proper IPM and for proper plant protection in organic farming. Insects can be monitored using a variety of monitoring tools such as: pheromone traps, light traps, coloured sticky traps, suction traps, etc. Pest monitoring methods are usually very time consuming and require significant investment in species identification after manual trapping in the field.

Trap catch data serves several purposes: 1. ecological studies; 2. tracking insect migration; 3. new arrivals in agroecosystems; 4. initiating field surveys and sampling; 5. timing of PPP applications; 6. defining phenology models; 7. predicting generation size; 8. pest control.

Predicting pests is an important part of the strategy of IPM as well as in organic farming. Early warnings and forecasts based on biophysical methods provide a lead time for managing an impending pest infestation and can thus minimize crop losses, optimize pest control, and reduce the cost of cultivation.

There is also a need to prevent secondary damage and spread through continuous monitoring by supplementing primary control with conscientious control according to planned pest management methods. As monitoring is carried out throughout the vegetation period, it is necessary to focus on a large area in a short period of time, taking into account the time when the damage occurred intensively and the time when control can be carried out.

Insect pests monitoring trough traps

Trap catches can warn of the presence of pests, hot spots, and insect migration and activity, and provide a relative measure of insect density. Comparisons of the number of adult pests trapped on specific sampling dates can indicate whether pest densities in crops are changing or remaining relatively constant over the long term. Evaluation of trap catches can help determine treatment needs, timing of applications, and effectiveness of previous control measures.

Among the various methods and devices used in pest monitoring, the most popular and widely used are sex pheromone traps for selective monitoring of individual flying species, light traps for flying species attracted to light, and coloured sticky traps for species attracted to colour. While adult males are usually caught in sex pheromone traps, adults of both sexes are caught in light traps and coloured sticky traps. Light traps and coloured sticky traps can be used to detect species presence and to study population distribution and movements (migrations in the ecosystem) in a given area. Sticky traps have provided interesting results and can be considered as unbiased recording systems. They do not require a power source and are inexpensive, but their inspection for identification and eventual collection of trapped insects can be difficult and time-consuming, and their handling is relatively cumbersome.

a) Sex pheromone traps

Pheromones are messenger substances used for species-specific communication. Normally, these pheromones are produced by females to attract males. Commercially, they are produced by synthesizing the appropriate components and putting them into dispensers that can be placed in traps of various designs, depending on the production.

Figure 2.3.Trap with pheromone (photo: Lemic, D.)

Sex pheromone traps are useful for monitoring pests that evade early detection of economic damage. Using pheromone traps (Figure 2.3), it is possible to monitor the occurrence and abundance of adult pests and predict crop damage in the following year. Once key habitat parameters have been identified, it is possible to predict infestation levels on an annual basis, thereby informing farmers of appropriate control strategies required for this and the following year's crop. For example, larval emergence can be predicted based on the abundance of adults and eggs in the year prior to repeated sowing of a particular crop.

According to good agricultural practice (e.g., Ministry of Agriculture), pest management must be based on population-level forecasts that comply with the principles of IPM. Determining the factors that positively or negatively influence or limit the growth of pest populations facilitates the development of IPM strategies aimed at slowing the spread of individuals and thus mitigating damage to crops at the national and possibly international level.

b) Coloured sticky traps

The coloured trap is the most efficient method of monitoring the crop for insect pests and can often indicate the presence of the insect early enough for other control measures to be taken. Sticky traps are used as one of the effective strategies for monitoring various insect species. They provide a simple method for estimating pest population density, require low cost and low skilled labour, and are helpful in developing an environmentally friendly control strategy. As a result of estimation with sticky traps, there is generally a reduction in PPPs use, which in turn leads to lower input costs, reduced exposure of workers to PPPs, and ultimately lower PPPs-related phytotoxicity and costs, which directly affect the quantity and quality of yields. Sticky traps are economically affordable as they cost less and require less technical work.

Sticky trap pest control uses an adhesive-based trap to monitor, trap, and immobilize pests. These types of traps are typically made of cardboard with a layer of sticky glue or plastic traps with renewable clue layer. The cardboard can also be folded into a tent shape or laid flat. The tent cover protects the glue surface from dust and other materials. Some glue traps also contain some type of scent to attract certain pests.

Figure 2.4.Coloured sticky traps (photo: Lemic, D.)

Sticky traps attract insect pests with a specific colour spectrum (Figure 2.4). They do not require bait or attractants but can be enhanced with essential oils such as Melissa, Lemon or Cinnamon Oil. Most animals exhibit the species-specific colour preference that corresponds to a specific range of the visible light spectrum in an individual. Insect colour preference is a rather striking phenomenon that has attracted attention in the basic and applied sciences.

Bright yellow (about 550 to 600 nm wavelength) is highly attractive to many insects. Adult whiteflies, thrips, leafminers, psyllids, shore flies, winged aphids, and parasitoids can be monitored with yellow sticky traps. As an example, the use of yellow sticky traps in seedling production with 1-2 traps/50-100 m2 can catch a significant number of whiteflies. Blue sticky traps are most attractive to western flower thrips and some other thrips species.

Traps provide a relative measure of insect density; comparing the number of adults trapped between sampling dates can indicate whether pest densities are changing or remaining relatively constant over the long term.

c) Light traps

The use of light to sample night-flying insects is a long-established technique. Light traps are most used to sample moth fauna (e.g., European corn borer Ostrinia nubilalis), but they also collect other insects, including adult aquatic insects (e.g., mayflies, dobsonflies, and caddisflies).

Depending on the intended use, there are many methods and variations that utilise an ever-changing technology. Light traps are best for population surveys or determining the geographic distribution of night-flying insects. This is because many species that are caught at night are practically undetectable using other sampling methods. Light traps for native insects potentially reveal a rich diversity of many different insects. It provides information on species diversity across all seasons, landscapes, ecological areas, elevations, and times of night. The light does not attract insects - it confuses them and takes them off their chosen flight path. Some insects fly repeatedly around the light, others simply settle at different distances from the light and fly away after different times. Insects see green, blue, and near ultraviolet (UV) light very well, but yellow and orange light they see poorly and red or infrared light they cannot see. Different types of light sources produce light at different wavelengths (colours) and are therefore differently effective for catching insects. Light traps are most effective for sampling night-flying insects in close proximity - up to 500 m from the light source. A light can be effective over greater distances - up to 1 km or more - if placed slightly elevated. Effectiveness depends on wind direction, as insects fly into the wind, and on wind speed, as many insects settle in strong winds. Flight activity also depends on temperature and humidity, and rain can stop or reduce it. Therefore, care must be taken when using light trap catches for comparative purposes such as monitoring. This requires keeping as many variables as possible the same or as close as possible each time. This is called standardisation.

Figure 2.5.Coloured sticky traps (photo: Virić Gašparić, H.)

There are many types of light traps; they can be powered by 240 V AC or 12 V DC, UV or white light (full spectrum) lamps, and they can collect insects live or act as a killing trap.

Collections from a light trap provide important information about the diversity of nocturnal insects, their respective affinities for different wavelengths of light, and for understanding and predicting how populations function. Such information, when properly documented, can be used by field researchers in multiple ways, such as selecting light traps to attract specific orders of insects.

The light trap's passive sampling, retention of live specimens, and low cost have led to its widespread use for recording insect diversity in terrestrial environments. For example, light traps have been used consistently and widely since the 1940s for standardized mosquito monitoring, as well as for monitoring moths and other species considered pests.