You bet they can!
Imagine for a second you are a parent and your child comes to you for help because his or her pet beetle has a broken leg and looks sick. Do you comfort the child by saying insects don’t have a sense of pain and can’t get sick or do you consult a book about Diseases of Insects and Spiders? There is after all quite a bit of literature about sick arthropods, e.g. A. Lewbart’s 2006 volume “Invertebrate Medicine” or the 2009 book “Insect Infection & Immunity” by J. Rolff and S.E.Reynolds. There are also articles like “Neoplasms of insects” by J.C. Harshbarger & R.L. Taylor or G. Vogt’s “How to minimize formation and growth of tumours:… decapod crustaceans for cancer research” or the review by F. Tascedda & E. Ottaviani “Tumors in invertebrates”. So, insects etc. can and do indeed get sick.
This is an issue not just for people who keep such invertebrates as pets, but an issue that is important for beekeepers, for people involved in the silkworm industry and other insect rearing ventures, for agriculturists and pathologists, generally. Why? Regarding honey bees and silkworms it is because of their importance and value that makes them so precious that they need a lot of care. But there are other reasons too: human medicine can learn from insects and how they deal with diseases that are often based on the same essentials: viruses, bacteria, fungi etc. and in the cases of cancers there are always mutated, rapidly proliferating cell lines involved. To fight the diseases, unifying principles are likely to have evolved over millenia in invertebrates which is why the study of the diseases of insects and other invertebrates is important and why journals like the “Journal of Insect Pathology” exist.
Viruses are known to infect various caterpillars and cause great losses. While this is welcomed by orchardists who wish to see their trees flourish and produce a good crop, it is bad news for people in the silkworm industry or those who try to breed and save endangered butterflies and moths. But the greatest fear is that of the apiarists, thinking of the health of their bees. Honey bees, being our chief pollinators, not only can contract a variety of sicknesses, they are also under attack from various parasites and one of them is the now almost worldwide Varroa mite. This little spiderlike critter sucks on the bodies of larval and adult bees and weakens them to such an extent that they experience weight loss and a much reduced life span. In addition, the wounds the mite leaves behind become a site for bacterial, fungal and virus infections (more than 10 kinds of virus diseases are known). Once established in a hive, Varroa mite attacks can spell the end of the bee colony and a variety of drugs is available to reduce or eradicate the ectoparasitic mites without harming the bees.
Another disease of bees as well as other insects and even crustaceans is caused by the microsporidian endoparasite Nosema, which is long lived. Once ingested it will reside inside the cells of the host’s tissue. In 1972 I examined by electron microscopy a microsporidian from the eyes of a staphylinid beetle and was amazed at the large number of cells affected. In bees the parasite lodges itself mostly in the cells of the gut and causes severe diarrhoea, possibly even fever. The disease weakens the workers and many die outside, not returning after foraging or not being able to fly, just crawling around. The Nosema parasite has to be ingested and is transmitted by mutual feeding or from a food source outside. If a queen happens to be affected, it would affect her ovaries and stop her from producing eggs. A Nosema species is also the cause of a silkworm disease known as pébrine, which causes the caterpillars to develop dark body spots and prevent them from spinning silk. Even more devastating to them is the infectious “flacherie”, a viral disease that leads to certain death.
Vaccinating insects? There is hope, because the Finnish scientists D. Freitak and H. Salmela appear to have discovered a mechanism to actually vaccinate bees against the devastating bacterial foulbrood disease. Simply put, when queen bees eat something with pathogens, the pathogen’s signature molecules are bound by vitellogenin, which transfers them into the queen’s eggs where they then act as inducers for future immune responses. Does it really work? The future will tell.
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