Perils of processing pitfalls

During the Fall and Winter seasons the IPM lab focuses on processing the numerous field-collected samples. One of these tasks is processing pitfalls. Pitfall traps are used to monitor insect pests, especially those that crawl on the surface of the ground like adult beetles. A pitfall trap consists of a small container filled with RV plumbing anti-freeze submerged into the soil so its opening is level with the soil surface (Fig. 1). A rainfall cover is staked to the ground 1” above the trap to keep rain and larger animals like mice out. The trap is left for seven to 10 days then the content is retrieved, labelled and preserved in ethanol and refrigerated until processed at a later date.

Fig. 1. Pitfall trap deployment consist of filling the container with antifreeze (A), placing the filled inner container into the pre-cut hole in the soil then protecting the opening with a rain cover (B), to produce a submerged pitfall trap whose opening is flush with the surrounding soil surface (C). Photos and diagram by Shelby Dufton.

During the Fall and Winter months, stored pitfalls are retrieved for individual processing via submersion in water. The samples, which are stored in cheesecloth bundles, are opened into a tray of water (~1.5 L water in a ~4 L tray) because arthropods normally float and most of the soil/rocks sink. This pre-sorts the sample. Elaterids, carabids, staphylinids, and arachnids are then hand-sorted, recorded, and transferred to labelled vials with 95% ETOH. They are stored for further processing, like sex determination and species identification.

Over the past month, Tia and I have been working on two main studies using pitfalls, the Canola Agronomic Research Program (CARP) project and the wireworm monitoring project, both of which are extensive projects with sites across the Peace River region. The wireworm project additionally involves testing pheromone lures used in pitfall trapping.

Fig. 2. Pitfall trap processing involves submersion of a muddy wireworm monitoring sample in a 38 cm by 23 cm tub containing ~1.5 litres of water (A) and carefully retrieving the many beetles and grasshoppers from the sample (B). 

It is important to monitor wireworms, which are actually the larvae of click beetles (Elataridae), because they can be harmful to crops throughout their lifecycle. Click beetle larvae, often referred to as wireworms, cause economic damage as they feed on germinating seeds and decrease both plant establishment and densities in all field crops. Pheromone lures attract wireworms by emitting the same chemicals as germinating seeds, which the wireworms detect when finding food. Pitfall traps mainly catch adult click beetles because the larvae live beneath the soil surface. For more information on how to check your field for wireworms, refer to the PPMN blog and field guide.

We also monitor carabid beetles retrieved from these pitfall samples. Carabids are important to the agroecosystem because this large group of species can be natural predators of click beetles. At least 16 species of carabids are commonly found in fields in the Peace River region. They range in size and color (Fig. 3).

Fig. 3. A selection of pinned Poecilus lucublandus (Coleoptera: Carabidae) from a previous project conducted at AAFC-Beaverlodge demonstrates the diversity in size (7-11 mm) and color (dark, iridescent greens, blues, and purples that can be much brighter in life than in pictures) even within one species. 

References: 
Philip, H. 2015.  Field crop and forage pests and their natural enemies in western Canada: identification and management field guide. Agriculture and Agri-Food Canada, Saskatoon, SK. Access the free PDF.