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#49: Spider Mites


Litinsects #49:

Month of Mites, Part 5

Let me introduce you to some pesky little dudes called spider mites. There are about 1200 species of spider mites and they are huge agricultural/commercial pests. The TWO-SPOTTED SPIDER MITE shown in these photos (named for, you guessed it, its two dark spots) is one of the most well-known and economically important pests worldwide because it feeds on hundreds of plant species. I worked with these mites as part of my master’s thesis and was able to witness firsthand how they can decimate plants if left uncontrolled!
 
  • So why are they called spider mites? Because they spin silk WEBBING that can cover entire plants. The webbing serves as protection for the colony from weather, desiccation, and pesticides but also protects from predators, who can’t maneuver through it very well
     

  • Spider mite females are larger, at around 0.5 mm and males are around 0.3 mm. The eggs are round and 0.15 mm in size. Just before hatching, the mites’ RED EYES are visible inside the eggs! 
     
  • Spider mites feed by penetrating plant epidermal cells and sucking out the contents, leaving characteristic pale patches on the leaves. A few empty cells here and there might not be a big deal but as you can imagine, the appetite of an entire colony will soon result in huge areas of empty plant cells, which eventually kills the plant due to its inability to photosynthesize
  • An interesting phenomenon seen in spider mites is ARRHENOTOKY, which I explained using the term HAPLODIPLOIDY in my post about hymenopterans (Day 33). This means that males are produced from unfertilized eggs and females are produced from fertilized eggs
  • Studies have found that these mites can probably RECOGNIZE who they are related to in order to avoid inbreeding! When given a choice between two males in an experiment, one related and one not related them, females were more likely to mate with the one they were not related to, pointing to some mechanism for recognition
  • And finally, as I first mentioned in my aphid post (Day 30), this mite is the only animal species besides aphids known to produce CAROTENOIDS themselves. All other animals get these red/orange pigments from plants or algae they ingest. Two spotted spider mites can do it thanks to a gene transfer millions of years ago from fungi!
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