Insect Sampling

Insect sampling techniques

Insect sampling involves the collection of insects in the field by entomologists. There are generally two techniques used to collect insects - active collecting and passive collecting. The collection technique used is dependent on the types of insects being collected.

Active collecting

Active collecting of insects, as it says, involves entomologists actively catching insects in the field rather than placing traps to check at a later time (Fig. 1). Active collecting is most often used to collect insects found in plants. Methods of the active collection include:

• "Beat sampling" involves the "beating" of vegetation to cause insects to fall into a net held below.

• "Sweep netting" involves a butterfly or insect net being used to sweep vegetation or water to catch insects.

• Hand collection of insects involves the catching of insects by hand. This can be useful to avoid catching or killing threatened species and is often used in conjunction with the above two sampling techniques.

These methods are beneficial for catching certain insects, such as beetles, bees, butterflies, caterpillars, dragonflies, grasshoppers, mantises, true bugs, and wasps.

Passive collecting

Passive collecting of insects involves placing traps to capture insects for collection by entomologists. Methods of passive collecting include:

• Pitfall traps are devices (such as buckets) that are dug into the ground so that the lip of the bucket is at the surface. Sometimes these traps are covered with camouflage, such as vegetation. Insects fall into the pitfall traps and are stuck there for entomologists to collect later.

  Wildlife biologists also use pitfalls to collect snakes and other vertebrates.

• Light sheets, which consist of white sheets suspended by poles with a fluorescent, mercury vapour (MV) or black (UV) light fixed next to them, are used at night to attract insects. Entomologists then collect the insects that land on the sheet.

  Light sheets have both active and passive collection components, though they are generally considered examples of passive collecting.

• Sticky traps consist of an adhesive plane that causes insects passing over it to become trapped. While sticky traps can be effective, they can kill insects and the specimens can be damaged or destroyed when entomologists attempt to retrieve them. Sticky traps are also often used to collect other invertebrates, such as arachnids.

  In addition to killing insects and arachnids, sticky traps can be problematic as they can kill non-target animals, such as rodents, snakes, and lizards.

• Pheromone traps are used to collect individual species through species-specific sex pheromones. As with sticky traps, pheromone traps often use adhesive surfaces to catch these insects.

  This is particularly useful when trying to capture particular pest species.

• Flight interception traps (FIT) involve a transparent surface/barrier, usually plastic, with a basin consisting of a preservation fluid or water, which insects would fall into for later collection. As you can expect, flight interception traps often result in the death of the insects that run into them.

  These traps can also injure or kill bats and birds.

Insect sampling equipment

Insect sampling requires specific kinds of equipment, dependent on what type of insects you are collecting (e.g., flying insects require different equipment than ground or plant-dwelling insects).

Regardless of what kind of insects you are collecting, however, there are a few essential pieces of equipment you will require:

• A notebook, pen/pencil, or a digital device to take notes and collect data, such as a smart tablet.

• Label stickers or cards to label specimens.

• Jars, vials or some other container for captured or dead specimens.

• Ethanol to preserve dead specimens.

• A GPS device to log capture and/or trap coordinates.

Active collecting may involve the use of the following pieces of equipment:

• A butterfly or insect net or a beating apparatus (Fig. 2).

• A collection device, such as a bucket, bag or net.

• Thick gloves if hand collecting, mainly if collecting stinging insects, such as bees and wasps.

Passive collecting may involve all of the preceding equipment, as well as more extravagant equipment, such as:

• Large white sheets, lights (fluorescent, MV or UV), and poles to suspend both.

• Adhesive surfaces to construct sticky traps.

• Large plastic sheets to build FITs.

• Buckets and shovels to create pitfall traps.

An example of insect sampling

Tarantula hawks are wasps of the family Pompilidae belonging to the genus of either Pepsis or Hemipepsis.

From 1999 to 2003, entomologists collected wasps in Big Bend National Park to study and better understand the natural history and ecology of two tarantula hawk species (Pepsis cerberus and P. mexicana) in Texas.

The entomologists collected the tarantula hawks using a combination of both active collection (sweep nets) and passive collection (light traps). The wasps were collected alive, had biometric data collected, and were kept captive to conduct observational experiments with captured tarantulas. Some tarantula hawks were also hand-gathered as they fed upon nectar, and notes were taken regarding which plant species they most frequented.

Insect surveillance and the importance of pest monitoring

When insect surveillance involves pest species, the damage to agricultural crops is recorded to determine mitigation and management strategies.

This monitoring of pest populations is vital to understanding pest population status, the threats posed by pest populations, and how to address them. It is also essential to determine the economic benefits expected from controlling such pests.

This can allow for "pest forecasting", which is the ability to forecast the potential quantity of pests and surges in pest populations. Pest forecasting can be either short-term (a couple of seasons) or long-term.