Wednesday, 7 December 2016

Large subterranean larvae in field crops

This week a query came in for large, thick-bodied white larvae found just below the soil surface that were clipping grass plants below the soil surface. An insect specimen will always help a trained entomologist identify a pest species with the greatest accuracy.  However, in the absence of a specimen, here's a short list of potential insects that might fit the above description and will hopefully aid scouting efforts in the spring:

1. June beetle larvae - These are large juvenile stages of the June beetle and they are herbivorous.  They are occasional pests but difficult to manage using foliar-applied broad spectrum insecticides since the larvae remain below the soil surface when feeding.  When scouting, be on the lookout for the creamy-white body colour, their larger size, the presence of a well-defined tan head capsule, and three pairs of legs on the anterior end.  Below is a screen shot extracted from the Insect Pest chapter prepared by Soroka & Otani in the Alberta Forage Manual below but download the entire manual here.

2.  Small Scarab Beetle Larvae - These are also juvenile stages of another beetle species and these whitish to creamy yellow coloured larvae will feed on a broad range of host plants.  Dr. Kevin Floate at AAFC-Lethbridge is currently taking specimens of larvae to help assess whether or not this species is an economic pest versus an occasional issue.  Link here to access Dr. Floate's fact sheet on the Prairie Pest Monitoring Network's Blog and note the similarities to the June Beetle larvae but know that the larva of the Small Scarab Beetle is "smaller".

3.  Cutworms - Several species of cutworms will occur in all of Alberta's field crops and careful scouting is needed early in the Spring (mid-April to mid-June).  Several species of cutworms are climbing cutworms and they are easiest to find in the evening or early in the morning since they feed above-ground on foliage.  Cutworms in grasses grown for hay or seed will be both climbing and subeteranean so pay attention when scouting since digging is often required in order to find the culprit.  Link here to read over an earlier post on cutworms on the Prairie Pest Monitoring Network's Blog and to access fact sheets for the various species.

Remember, the above list is NOT complete.  Specimens should be examined to help identify the species and to ensure scouting and control options are applied appropriately  - after all, cutworm scouting and control strategies don't necessarily help if June Beetle larvae are in the field!