Tuesday, May 14, 2013

Scouting for Sawfly larvae

    Every since the arrival of clear sunny weather, I been looking for the sawfly larvae that feed on expanding pecan foliage. Once the larvae become active, the damage is fairly easy to spot. You will find a cluster of small holes cut into leaflet blades (photo above, right).
    These small holes were created by the feeding of Periclista marginicollis (Norton), a small green sawfly larvae (photo at left). When inspecting damaged pecan foliage you will usually find these insects on the underside of leaflets. Full sized large grow to about 9/16 inch long before dropping to the ground to pupate. There is only one generation per year.
   In the past, we have experienced severe outbreaks of this pest. Larvae became so numerous that trees were defoliated. Although outbreaks of this sawfly are rare, we scout the pecan grove every spring to avoid letting this insect become a problem. 

    Chewing large holes, or entire leaf blades is another, less-common sawfly. The larvae of Megaxyela major (Cresson) is yellow in color with prominent black spots and a black head capsule. Larvae grow to 3/4 inch long before dropping to the ground and pupating. This sawfly has the curious habit of curling around a leaf's rachis or midrib during daylight hours (photo at right). As night falls, the larvae continue to feed on entire leaves often leaving just the midrib. We have never had a serious outbreak of this sawfly species.