Urban Society (of Insects)

Last Friday my colleague Gene Hall showed me some Monarch caterpillars that are growing up on Desert Milkweed plants on campus.

The plants are snug against the south-exposed brick wall of the Chemistry Building, so if the caterpillars survive the periodic drastic clipping by U of A gardeners, they have found a microhabitat that will sustain them even during the colder weeks of winter.
We found very small caterpillars around a centimeter in length, probably second instar, and a few that were more than an inch long, indicating that at least two females were ovipositing here lately. I did actually see two adult Monarchs in Marana last week. All these observations are data points off the main eastern or western migration route of the majority of Monarchs, but storms displace a number of them each year and we also seem to have some small, but constant populations around Tucson.

 I took the opportunity  to photograph groups of bright yellow Oleander Aphids (Aphis nerii) that commonly feed on milkweeds. Besides hundreds of wingless individuals one group also included a few winged females. One of them was very freshly molted and teneral, with still soft wings and without mature pigmentation. (I will try to describe the complexities of Aphid reproduction and generation sequence in another chapter).

On the enlarged images I later discovered a syrphid larva that was feeding on the aphids (bottom left). It was nearly transparent and moved inconspicuously among its victims.

The syrphid larva could be the offspring of the male  Bird Hoverfly that I had photographed a couple of days before in the same area.

An only  2 mm long Dusky-colored Ladybug, a species in the genus Scymnus, was also preying on the smaller aphids.

During the photo session, an Ichneumon Wasp appeared. It flew around the milkweed stalks as if searching for something, and I assumed that the parasitic wasp was planning to lay its eggs one of the Monarch caterpillars. When it landed very shortly, I managed only one unfocused shot, just for documentation. But it was enough: from the blurry image plus the description of the situation Bob Carlson on Bugguide was able to narrow down the identification to the subfamily Diplazontinae. All species of this group are believed to be parasitoids of syrphid larvae.

So with our short lunch hour excursion and some follow-up research we had discovered a whole complex ecosystem of herbivores, predators, and a parasite of the predator. All that right next to the wall of the Chemistry building, in an unpaved area that is only a few inches wide.

In the interest of full disclosure, there were also two ornate Tree Lizards, several Small Milkweed Bug nymphs, a Gray Bird Grasshopper and a  Smoke Tree Sharpshooter hanging out among the milkweeds.  Some, like the bug nymph, were there to sip the chemical cocktail provided by the milkweeds, others probably mostly to get warm on the sun-exposed bricks. Either way, it takes care of the energy budget.

True Bugs on Cactus

True bugs suck!

There are times in Arizona's Sonoran Desert when cacti and agaves are about the only juicy things for a bug to suck on. Cactus specialists among the hemipterans can be found during all seasons, even reproducing in the middle of winter.

The species of the coreid (leaf-footed bug) genus Narnia specialize on different cacti. Some of them can be found on Prickly Pear, another that seems to be undescribed so far, prefers Saguaros.

 

Several species, like for example Narnia wilsoni spend their lives under the formidable protection of the thorns of the Fish-hook Barrel Cactus. The freshly hatched first instar nymphs above are enjoying the juicy film that covers the fresh seeds after a squirrel broke into the fruit. 

 

 

Of course, no protection is absolute: This older nymph, still red (teneral) and soft after its last molt before reaching adulthood, fell victim to a jumping spider. You can see the exuvia (shed skin) at the top left and a string of new eggs on the thorn on the right. So I guess this rare species will survive here in our backyard.

Adult Narnia wilsoni

N. wilsoni adults are quite attractive. Most others in the genus Narnia are drab and hard to tell apart. And who knows whether the species is really so rare. Hidden deeply between the ribs of the barrel cactus these guys are very hard to spot.

Two more coreid species Chelinidea vittiger and C. hunteri also frequent our succulents. Their contrasting wing vein pattern and subtile coloring remind me of my grandmother's Art Deco jewlery.

The nymphs with their thick antennae seem more in the style of children's plastic toys. Parental guarding is common in these bugs.

A couple of days ago I found the odd looking Merocoris sp., also a Coreid, on an Engleman's Prickly Pear in our back yard. It can't be an obligatory cactus feeder, because it also occurs in the Sonoita Grasslands where there is hardly any cactus. But it was definitely sucking from the succulent little leaf remenant on the Opuntia bud.

Despite their plump shape and suggestively big hind thighs, these coreids are no jumpers, but they can fly.

Merocoris sp.

Some Stinkbugs or Pentatomids also have cactus as a preferred host plant, like these Chlorochroa opuntiae. The  little congregtion below was photographed in September 2010 in the Saguaro Monument West in the Tucson Mountains. The individual below was feeding on a Cane Cholla in our backyard (bajada of the same mountains) on March 29, 2011.

Chlorochroa opuntiae

Zelus renardii, Leafhopper, Assassin Bug

Growing cacti release sugary juices from extra-floral nectaries and just growing  pads and flower buds.  A predatory bug, a reduviid in the genus Zelus, is stalking  insects that can't resist the sweet attraction.  

Small Milkweed Bugs Lygaeus kalmii

These Small Milkweed Bugs  in the Seed Bug family will most likely not lay their eggs on the agave leaf that they chose as a mating place, but the closest relative to milkweed in our backyard are some Oleanders that survived the 'renatification' of our property.