Friday, July 04, 2014

Wheel Bugs Vs. Walnut Caterpillars

Two days ago, I noticed a mass of small, hairy caterpillars on a single leaflet of a pecan leaf.

Today, I took a close look at the pecan again and discovered 3 separate masses of the hairy caterpillars, which I later identified as walnut caterpillars, Datana integerimma, a well known pest of walnuts and pecan trees.

Two of the groups of caterpillars seem to be developing with little interference, at least so far.  The above group was the furthest along in their development.  I need to decide what, if anything, I am going to do about them.

Meanwhile, the third group of caterpillars had attracted some attention.  Some lethal attention, actually.  Two wheel bugs had positioned themselves between the caterpillars and the healthy leaves of the twig they they were on.

Both wheel bugs had caterpillars that they were feeding on.  They appeared to be capturing each caterpillar as it attempted to move to a new leaflet to feed.

Wheel bugs, like most predatory insects, are VERY aware of their surroundings.  It is hard to sneak up on them, and these two were no exception.  As soon as they saw me, they hid...and every time I repositioned, so did they.

One shot I got silhouetted one of the wheel bugs eating a caterpillar against the sky.  I found that the sight of the wheel bug's pair of legs, locked around the central rachis of the pecan leaf as it fed, made me feel almost protective of this fierce predator.

(Note:  The caterpillar is the slightly hairy thing, hanging from front of the wheel bug.)

Anyway, according to the information sites that I found on the web, I probably should get rid of these caterpillars while I can.  This is probably the first generation...and there is usually a second generation too.  The caterpillars usually cause their most extensive damage in the last instar before pupating; then the second generation will cause more damage, as it's likely to be larger.

The wheel bugs will presumably take care of the one cluster that they are systemically guarding and eating.  That leaves the other two clusters.  If I destroy them by plucking the leaves and drowning the caterpillars in soapy water, I may be able to keep further damage from occurring.  But then there is no further chance for other predator or parasite numbers to increase.  According to the Forest Service information sheet that I linked to above, there are at least 13 parasites known to attack these caterpillars, as well as several predators (such as the wheel bug and certain spiders), and viruses and other diseases.

For now, I think I will let nature take her course and just observe.  Reality "television" at its most real!

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