Insects are some of the most numerous organisms on Earth, with over one million species currently recognised. Insects also have fast generation times, allowing for quicker evolutionary change and the potential emergence of new species. Considering all of this, you may wonder how scientists can assess and quantify such populations. The answer is through a process called insect sampling.
What is sampling of an insect population?
Insect sampling refers to monitoring insect populations to determine insect biomass, the status and distribution of insect populations, and the presence and status of pest species. Insect sampling is used to sample insects in all habitats, including soil, vegetation, and flying insects.
Insect sampling is particularly vital for agricultural operations, as pest species can decimate crops.
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.
Entomology is a branch of zoology that quite literally translates as "the study of insects" from the Greek words "entomon" (insect) and "logia" (study of).
Entomologists are scientists that study insects.
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.
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:
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.
Tarantula hawk obtained their common name because they attack and paralyse large spiders of the Theraphosidae family to lay their eggs on them.
Allowing the hatching larva to consume the paralysed but alive spider.
Tarantula hawks are some of the world's largest wasps, with bodies reaching a length of two inches with long stingers capable of inflicting an excruciating sting, second only to the bullet ant (Paraponera clavata).
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.
This is a fine example of insect sampling and surveillance of potentially dangerous insect species.
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.
Insect surveillance is a form of insect sampling involving consistent insect population surveillance.
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.
Such as increased citrus crop production.
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.
Insect Sampling - Key takeaways
Insect sampling refers to monitoring insect populations to determine insect biomass, the status and distribution of insect populations, and the presence and status of pest species.
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.
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. Examples include "beat sampling", "sweep netting", and hand collecting.
Passive collecting of insects involves placing traps to capture insects for collection by entomologists. Methods of passive collecting include pitfall traps, light traps, pheromone traps, sticky traps, and FITs.
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