Icerya purchasi (''cochinilla australiana'') on citrus twig | western Buenos Aires Province, Argentina
After traveling through the northern provinces during late March and early April, I returned to my home base in western Buenos Aires Province for the last two weeks of my stay in Argentina. As soon as I could, I returned to the small grove of planted citrus trees on the station grounds where I had found a rather large, beautifully cryptic fulgorid nymph (see “Seeing the unseen“). Lois O’Brien had mentioned in her response to my query about the identity of the nymph that some species of Fulgoridae tend to live on the same tree for years and years—if I could go back to the tree on which I found the nymph perhaps I could find the adult. Sadly, no adults or additional nymphs were found, either on the original tree or any in its vicinity. What I did find, however, was this strange, cocoon-like structure on one of the branches of the tree. I had no idea what it was, having never seen anything quite like it, but I figured something—pupa, eggs, parasitoid, etc.—must be inside. I cut the piece of branch with the structure and tucked it inside a vial for later.
Egg case opened to reveal eggs and newly hatched nymphs
A little bit of searching online would have quickly told me what I was dealing with, but for some reason I felt the need to go ahead and start dissecting to see what was inside. It became obvious I was dealing with an egg mass when I peeled back the outer layers to reveal the cluster of red eggs inside, and very quickly I noticed that a few of the eggs had already hatched. The red nymphs had a decidedly “homopterous” look to them, and not much effort was required to figure out that I was looking at my very first “cottony cushion scale” insect.
Closer view of eggs - newly hatched nymph can be seen at bottom.
Icerya purchasi (Hemiptera: Monophlebidae) originally hails from Australia, but its preference for citrus and the realities of global commerce have resulted in its inevitable spread across the globe wherever citrus is grown (maybe I can be forgiven for having never before seen such a widespread insect—living most of my life in Missouri and northern California, I’ve not had much opportunity to visit citrus groves). The English common name clearly references the appearance the adult female, recognizable by the white, fluted egg sac shown here, while in Argentina it is called “cochinilla australiana”—literally meaning “Australian scale insect.”
Newly hatched nymphs are bright red with dark antennae and thin brown legs.
As I dissected the egg sac, a few of the newly hatched nymphs crawled out of the sac an onto the branch. Nymphs of this stage are referred to as “crawlers” because they are the dispersal stage. It’s a good name for these tiny little bugs, as the several that I tried to photograph never stopped moving. With the lens fully extended to 5X, it was difficult enough to just find them in the viewfinder, much less compose and focus with all the movement. It became a numbers game and test of patience—how many shots could I get fired off in the amount of time that I was willing to persist? Shown here are the few shots that I was the least displeased with.
First instar nymphs are the primary dispersal stage.
Crawlers disperse not only by crawling, but also by wind. One can imagine that such tiny insects could easily be picked up by the wind and carried long distances. However, I couldn’t help but notice the very long setae on the body and outer antennal segments (visible to greater or lesser degree in these photos) and think that perhaps they have some function in aiding wind dispersal. At the very least, aerial dispersal must be as important as crawling (if not more so) for colonization by this species—only adult males have wings (but they are rare), while egg-laying females (actually hermaphrodites) are completely sessile.
Do the long setae on the body and antennae of the nymph aid in wind dispersal?
The adult female and egg case may have confused me initially, but a ton of readers had no problem figuring out what it was. A record 24 people participated in this challenge, with all but five correctly guessing the species. Winning this challenge came down to bonus points for speed and uniqueness of additional information, and Christopher Taylor did this best to earn 17 pts and the win. Three others—Brady Richards, Mr. Phidippus and bicyclebug—each finished just 1 pt back of the win, but Sam Heads’ 15 pts keeps the overall lead in his possession. BitB Challenge Session #6 is young, but already a lot of people have a lot of points in the bank. It will be interesting to see how this session develops.
Copyright © Ted C. MacRae 2012
Beetles In The Bush 