Two animals, a fungus and a houseplant — Part I. The scale insect

Anyone who tends houseplants indoors knows the risk of inviting other uninvited guests — in particular various arthropods and fungi. However, with a foldscope this transforms into new material for investigations. I have been growing a wood-apple tree (called Bilva in India; Aegle marmelos) for a few years now. This is a very popular and hardy tree in the Indian subcontinent and grows very slowly. In winters, my plant resides indoors in comfortable heated environments and year after year, it gives me heartaches with the pests it attracts when inside. However, a pest is only a human perspective, the evolution of flowering plants and insects is very intimate and goes back 250 million years, way before our primate ancestor existed– so from their perspective I am perhaps the pest.

In any case, a few days ago, I noticed that several of its leaves were shiny and sticky and there were little waxy bumps on the leaf surface. There was also a black growth. I knew I had double-trouble. The waxy protrusions are scale insects, members of the order hemiptera that suck the sap drawn from the plant’s vascular system and secrete a sticky and presumably sweet honeydew. This promotes the growth of a black fungus that can inundate the plant preventing it from gaining access to light and making it look rather unaesthetic. This also may attracts ants. Additionally, while I watered the plant a few fungal gnats startled from the stream buzzed around the soil and they seemed to be thriving in my negligence. However, now along with my plant were two animals and a fungus– all great material for a foldscope party. In the first part, I shall describe some images of the scale insect.

New folderScale insects are hemipterans of the Stenorrhyncha type closely related to aphids and white flies. All the scales I saw on my plant are likely to be female.  For this, I took a cellophane tape and placed it over the leaf and pulled out the scales (they came off easily) and stuck it on a glass slide. Under a 40x microscope here is what a scale looks like. You can see the eyes of the female (two dots) in the anterior end (top left). Legs and antennae are not seen because by the time this female scale becomes an adult it either loses these appendages or they are very reduced in size compared to the rest of the body. The female sticks its proboscis into the leaf vasculature, secretes honeydew and makes descendants. The female scale insect encloses eggs and nymphs at various developmental stages in a brood chamber.

scale1Within the mother scale insects, I could spot several stages of development of the growing nymph (see foldscope images below). The eggs with yolk granules, the nymphs with eyes and no appendages, that with appendages, and the crawler ready to leave from the mother scale. This form of development is called ovovivipary where the eggs remain within the mother until they hatch. The eggs however are nourished by the egg yolk and not the mother as in viviparous animals.

scale2Upon completion of the first instar (under the mother’s care), the nymph is called a crawler and has appendages and antennae and leaves the mother scale to found its own colony. I realized to my horror that if one scale had these many scale-lings, I am done for! Here is a nice picture of the crawler showing all aspects of scale insect anatomy (Foldscope 140x).

scale3

Since I have a new-found love for my own movies, here is one showing a scale with nymphs and eggs at various stages of development (Foldscope 140x).

Here is another one combining two videos. In the first, you see these beating tubes in the scale (are they the multiple hearts? of the insect or perhaps a digestive action of sucking and excretion, both of which the scale does in plenty), and in the second two crawlers (now past their first instar) are trying to emerge from the mother scale insect.

Thus far I know that this is a soft-scale insect and would be classified as hemipteran -> Sternorrhyncha > Coccidae. There is this wonderful website for identifying scale insects http://idtools.org/id/scales/key.php?key=soft.  I realized that there are several key characters one should pay attention to, such as number of antennal segments and the presence of marginal setae in the adult female scale for identification. However, with great impulse and curiosity, I shot an email to a leading expert on scale insects and he, to my delight, replied immediately that it was a brown soft scale (Coccus hesperidum). Also this far, as far as I can see, there were no males as they appear to be only occasionally produced and the adults are winged, but perhaps it is not the season for them, or perhaps I am not looking  for them properly.  Now all this means that I need to read up on Coccus hesperidum and recapitulate observations already made and reported in the literature (Sometimes I wish I was 10 again) and look for new things. Happy to learn about scale insects. Now onwards to the fungus. To be continued ….

7 Comments Add yours

  1. Niramay Gogate says:

    This whole article is just amazing. I liked the way you described everything . Can you just do similar analysis for red spider ants? They are often found on rose leaves during Monsoon. Unfortunately I haven’t received my foldscope yet ; otherwise I would have done it by myself.
    This creature is quite amazing because it always carries a big bubble on its back . It is just perfect for foldscope party! 🙂

    1. laksiyer says:

      If you mean the red spider-mimic ant, I have not seen them here (NE USA), but there is a red spider-mite that only comes a few months later, by which time I will get to see images from your foldscope 🙂

  2. Manu Prakash says:

    @Niramay – can you please send me your address as an email at manup@stanford.edu; I should ship you a kit ASAP 🙂

    @Laksiyer – with this post, you have out done anything I could have imaged. It is such a pleasure to read this. Amazing!! Now I am wondering if I can find these guys. I am in disbelief to see them embedded in the leaf tissue.

    Also, I just got original translations of some of the oldest microscopy papers in the Royal Society archives. Adventures does not even begin to describe the same.. the playfulness of these posts makes me realize how important it is to present observations as they happen. It’s like reading someone’s mind as thoughts take place. How and why we analyze – just marvelous.

    cheers
    manu

    1. laksiyer says:

      Hi Manu: To be frank I have always loathed scale insects until now. However, having looked at them, I realize they are a perfect case to study the development of Hemimetabolous insects as you can see all the different stages of development under one roof (No special preparations are needed either). The observations of Leeuwenhoek are a pleasure to read (I have only read excerpts), much like the diaries of Charles Darwin. Are they freely available, these translations?

      You have given amateur scientists a new life with an affordable microscope and a place to put up observations and thoughts. Perhaps one day we can really do something big like the AAVSO for variable stars, where amateur contributions help professional scientists. I have been thinking about how it would be if we could monitor pollen counts across the seasons. Will it help if 10,000 people are doing it in one local area vs the weather station? What might we learn? Each individual will carry a pollen monitor badge (paper slide with two sided tape of fixed area) and count the number and types of pollen at the end of the day and put it up on a website. The people most interested would be those suffering from allergies. Arm-chair ideas I love them.

  3. Niramay Gogate says:

    To be frank , I have very less knowledge about them. You can get the exact idea of what I am talking about, if you see their pictures. My elder brother has taken their pictures with SLR camera. I can send them if you want.
    -I am from India and Indian rose plants are often affected by these insects.

  4. Niramay Gogate says:

    @Manu- Thank you for helping me.
    I have just sent an email to you.
    @Laksiyer- The insect I am looking , is only seen in Monsoon.

  5. Malhar says:

    @Laksiyer amazing post! It was so clear and precise! I can’t wait to read part 2,3 and 4. Your pollen idea is also really interesting. If we could, using the pollen badges, identify and map the progress of pollen with respect to continental winds and weather patterns, that would be pretty phenomenal. I would love to help out with this, but my Foldscope, like @Niramays, has not reached as of now. Keep up the good work!! 🙂

Leave a Reply