Wednesday, February 3, 2016

Sundew Assassin Bug

Assassin bug nymph - Mark Bower
While photographing lichen on Monday, Mark Bower came across this insect trying to look inconspicuous on a lichen covered stick.  It had the typical morphology of an assassin bug nymph, but which one?  I sent it to Bugguide and got my answer within 30 minutes - the Sundew Assassin Bug,  Zelus luridus.

Prominent spines on pronotum - Mike Quinn
Z. luridus adults are basically green with a few color variations  (luridus = sallow, ghastly).  The nymphs can vary from bright orange to blended mixtures of green.  According to Bugguide "The best feature for recognition is the pair of delicate spines on the rear corners of the pronotum, which are rather long on the light colored individuals and shorter on the dark."
Z. luridis nymph - Mark Bower

Both adults and nymphs prey on a wide variety of insects such as weevils and leafhoppers but much of their diet is lepidoptera larvae including butterfly caterpillars and many economic pests such as cotton bollworm.   They can be considered "good" or "bad" from our perspective but as usual, it depends, and they don't seem to care what we think.

Adult luncheon date
A quick trip to a favorite insect site called* brought up lots of good stuff.  Z. luridus has a cool predation strategy, or should I say sweet one.  They secrete sticky substances from glands on the tibia of their front legs.  This covers the hairs allowing them to capture their prey rather than relying on stabbing them like most other assassin bug species.  After that it is the same old story - inject digestive juice, wait and then suck out the digested contents.  Not exactly gourmet dining but it works for them.

A leafhoppers nightmare, Z. luridis egg mass and hatchlings -
The nymphs pass through 5 instars (stages) on the way to adulthood.  While they may commonly overwinter as eggs, Mark's didn't get the message and was moving about on a cold winter day.  Bugeric points out that the nymphs don't produce the sticky secretion but instead wipe them up from secretions that their mom left on the egg sac.  Details like this always make me wonder who bothered testing these tiny nymphs and how.  Here you can read the answer - C. Weirauch- 2006 described assassin bug methods of prey capture in detail.  Studies like this add up to the complete descriptions in field guides.

* Bugeric's blog is a great place to check for insect lore.  He is the author of my favorite insect field guide, Kaufman's Field Guide to Insects of North America.

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