Anti-insects nets are a physical method of crop protection that has been widely used in many areas of the world in recent decades. These textile physical barriers were initially used a few decades ago with the aim of preventing bird damage and protecting plants from strong winds. At that time, they were sparsely woven nets with few threads per unit length in each of the main directions of the fabric. Soon their potential as a pest control method was recognized, and denser nets were manufactured, which yielded excellent results by preventing or reducing insect access to plants.
The problem is complex because it is not enough to create a net with tiny pores that insects cannot pass through. As the pore size decreases, the porosity of the fabric also decreases, making it difficult for air to circulate around the plant, resulting in certain drawbacks. Therefore, the pore size must be optimized according to the specific species targeted for control.
Fig. 1. Adult individual of Frankliniella occidentalis on an anti-insects net.
Based on the above, anti-insects nets should be designed taking into account the specific pest (Bemisia tabaci, Drosophila suzukii, Frankliniella occidentalis (Fig. 1), Aphis gossypii, Driocosmus kuriphilus, etc.) being targeted. Since different pests have different morphologies and morphometrics, the suitable net will vary for each pest species.
Traditionally, the insect dimension considered when choosing the appropriate net has been the thorax size (in cross-section). Additionally, average body values of insects have been taken into account for selecting the most suitable anti-insects net. However, considering that insect populations, like human populations, exhibit variations in height, build, etc., this criterion is not very fortunate. Therefore, recent design trends are leaning towards morphometric studies of insect populations to determine size references (percentiles) related to smaller individuals.
The problem of insect size presents additional difficulties. It is important to note that insect size generally depends on temperature. Thus, insects tend to be smaller at higher temperatures compared to lower temperatures. Additionally, it is important to consider that females are usually larger than males.
It is important to keep in mind that the pore dimensions of insect-proof nets commonly used are average values. Therefore, it is necessary to require manufacturers to provide parameters that guarantee pore uniformity, so that these average values are representative of the entire fabric.
Another fundamental aspect to consider is that not all nets with the same thread density, for example, 20×10 threads/cm², are the same. This is a common and serious mistake. To determine the average pore dimensions, the thread density value must be accompanied by the thread thickness. Consequently, it is easy to understand that a net woven with 20×10 threads/cm² and thick threads (e.g., 0.25 mm) will have smaller pores than a net with the same thread density but woven with thinner threads (e.g., 0.22 mm).
Special thanks to Álvarez AJ, Oliva RM from the University of Almería, Department of Engineering (Agrotextiles Laboratory) for sharing their knowledge in this space www.greennetsagro.com.