For reference, I am a plant pathologist by training. This means that the focus of a good chunk of my studies has been centred on organism or factors that cause disease, whether a bacterium, fungus or perhaps an abiotic (non-living) process. Despite my tendency towards all things rotting, in my work over the past decade I have developed a fascination for unusual insects. More often, it is the strange things that they do to plants to hide or protect themselves or as they feed that catches my eye.
Insects can do an incredible amount of damage to plants. Some insects eat specific layers of cells, or suck the juices out of plant parts or do whatever they do best to eat and thrive. Some insects just sit out in the open and feed, in some cases consuming foliage at an amazing rate. This sort of damage is fairly obvious. Other insects are more subtle (or wise, that is debatable), preferring to create shelters to protect them while they feed, grow and develop. Some choose something in between.
What is really neat is that sometimes the insects (or insect-like pests) that cause the biggest, most obvious injury or damage symptoms are actually tiny immature insects. What follows is a rogues’ gallery of some of the interesting insects that I’ve come across over the past few years. I’ll try to break them into sections of similar actions or similar species. Since I am not an entomologist (a.k.a. Bug guy), my groupings may offend those with more training or education. Too bad, so sad. In this, I’m in it for the entertainment value. In some cases, some of the insects that I share with you could fit into several categories.
Lots of insects go to great lengths to conceal or protect themselves from harm during development and end up producing are some wild symptoms.
Maple Leafcutter (Paraclemensia acerifoliella)
This insect has a history in other regions of causing a fair bit of damage to maples. In Alberta, there wasn’t really a record of it until a few years ago, when it was discovered on an entirely different species, Saskatoon berry (Amelanchier alnifolia). This insect skeletonizes (feeds on the surface leaf tissues) from underneath a shield that it creates from two pieces of leaf. As the larva develops, it has to replace the shield with a bigger one. The feeding damage is unique and the shield sticks out, however, you do have to dig and peel to expose this critter.
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| Maple leafcutter - shielded insect |
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| Maple Leafcutter - shielded insect under cover, preparing to cut a new shield (lower left); previously cut out leaf tissue evident (lower right) |
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| Shielded insect revealed within 2 layers of leaf shields |
Meadow Spittle Bug (Philaenus spumarius)
This little critter creates a froth of its own spit to hide within, feeding on the plant. The froth is pretty gross, but overall the damage created isn’t severe.
In some cases, insects create their own shelter from their own materials.
In the case of the Pine Needle Scale, which affects spruce, pine and firs, the coverage is a bit of waxy armour that is excreted by the females as they sort of suction cup themselves to the needles, remaining there for the duration of their lives, as they lay eggs underneath them.
The presence of scales resembles what I’ve seen described as “paint splatter”.
The crawlers (the immature form) emerge to move briefly before settling in to feed on the needles (they pierce and suck).
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| Pine needle scale - "paint splatter" symptom |
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| Closer view of Pine Needle Scale insects on srpuce needles. The black specks are the emergence holes of the "crawlers" (immature stage) |
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| Pine Needle Scales - white spots are the female scale insects that have attached themselves to the needle to feed, lay eggs and protect the eggs and young crawlers |
Leafminers (range of species)
There are many different leafmining insects out there. These insects lay their eggs into the cellular layers between the outer epidermal layers and the larvae feed and grow with this improvised pocket until they are ready to chew a hole and drop to the ground to finish their development over winter. Some leafminers chew channels or tunnels, other just go to town within the entire area, as is evident with the Birch leafminer
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| Birch leafminer - note the pockets that form from feeding on the tissue layers underneat the epidermis and cuticle, as well as the frass (poop) that is visible as dark brown/black powder in the lower parts of the bubble |
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| Another type of leafminer, this time on willow. The feeding is more like tunnels rather than an enlarged pocket |
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| Birch leafminer on Cutleaf Weeping Birch - tan brown areas are indicative of feeding and infestation; occasionally, in younger infestations, the larva will be visible moving around in the pocket |
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