Thursday, 16 June 2016

2016 Natural Enemies Project

There has been much going on so far this summer with our Wheat Midge Natural Enemies Project.  So far, we have seeded our plot trial and have been collecting samples from the plots using a method called pitfall trapping.  This is similar to what Hannah described here for the pea leaf weevil but these traps do not use a lure. The pitfall traps used for this study are comprised of two containers and a funnel made out of the top portion of a 2-Liter pop bottle.  As they are walking along the soil surface, arthropods fall into the funnel and slide down into the trap, which contains a mixture of antifreeze and water.  This solution kills and preserves them until we collect them each week.

Figure 1.  (A) The pitfall trap sits flush with soil in the middle a row in each plot. (B) The pitfall sample after the inner container has been removed.  Specimens are preserved in antifreeze solution which is the pink liquid that can be seen in the photo.

The pitfall traps collect a variety of arthropods which includes a fascinating array of beetle species.  The beetles we collect come in all shapes and vary from 2 mm to 4 cm in length.  Some of the most exciting of these are the beetle predators which are one of the main focuses of this study.  The goal of this project is to provide a unique comparison of beetle diversity and the rotation practices utilized by growers in the Peace River region.

Figure 2.  The biodiversity of beetles collected in wheat can be seen in this sample from the 2015 pitfall trap collections.

Ground Beetles
Carabidae, commonly known as ground beetles, is the largest family in the suborder, Adephaga, which comes from the Greek adephagos or ‘gluttonous.’  Gluttonous goes a long way in describing this family, as ground beetles are voracious feeders and often are cited as important predators.  Ground beetles are known to feed on aphids, cabbage root flies, Lepidopteran larvae, and many other pest species.  Carabid beetles make up the vast majority of the beetles we pick up in our pitfall traps.  Keep an eye out for them in the field; they have long slender legs made for running and vary in color.  Dark coloration generally denotes nocturnal species and metallic coloration usually indicates species that are active during the day.

Tiger Beetles
Though they may look quite different, tiger beetles are a sub-order in the Carabidae family.  Tiger beetles have long, sickle shaped mandibles (mouthparts made for chewing) and bulging eyes.  The larval stage of these beetles is known to create tunnels in the soil substrate.  There, they lie in wait to ambush prey at the opening of the tunnel.  When their prey walks by, the larva grabs it and drags it down to the bottom of the tunnel to feed.  The adults of these species are rapid fliers and have distinctly long legs that allow them to run quickly over the soil surface.    

Rove Beetles
Staphylinidae, or rove beetles, are another important family in terms of predation.  Rove beetles typically have shortened elytra that do not completely cover their abdomen.  Elytra are the hardened forewings that characterize all beetles.  Having shortened elytra allows rove beetles to maneuver more readily in the field.  However, there is a trade off - shortened elytra expose them to a greater risk of desiccation which makes them dependent on humid habitats.  Rove beetles are great predators and can even be parasitic.  Check out this link to see one of the parasitic rove beetles (Aleochara spp.) that emerged from a cabbage root fly pupa that we collected in October 2015.


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