Can Insects Get Sick and Develop Tumours?

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.

This cute little Naga girl wanted to know if the insect in the jar was sick.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

Most Insects have Five Eyes

Really, is that so?

Most people know that insects have compound eyes with often hundreds and even thousands of hexagonal facets. But what most people do not know is that many insects in addition to the two large compound eyes possess also an additional three much smaller single lens eyes (known as ocelli) on their forehead. These extra eyes are usually arranged in a triangular position on the insect’s forehead with the two lateral ones placed a little higher alongside the single, median ocellus.

Despite the huge amount of research that over the years has been conducted in connection with the compound eyes’  structure and function and has led to a considerable amount of understanding how the visual signals are received, analysed, transmitted to the insect’s brain and the elicit behavioural responses, the role (or roles) of the ocelli are still not fully clear. Although there is some evidence that they help a flying insect to maintain a balanced course and that damage to the ocelli, at least in some insects, interferes with their orientation mechanism, it is puzzling why members of some insect orders possess ocelli and others do not. If the ocelli, as another functional suggestion has it, work in concert with the compound eyes and analogously to a photometer prime the compound eyes by setting up their overall sensitivity to the ambient light level, then one could have perhaps expected to find ocelli in all insect species, but that is clearly not the case. Ocelli are almost always present in those insect orders with aquatic larvae like dragonflies, mayflies, stoneflies and some caddisflies. But they are absent in virtually all 400,000 or so species of beetles and in butterflies, bugs (Hemiptera), lacewings,  scorpionflies and true flies (Diptera) some have them and some do not. Ants, wasps, bees, etc, almost always have them, but so do the unrelated winged termite castes.

Structurally these little eyes, where they are present, are rather similar. There is, as could be expected, some variation with regard to the diameters of the ocelli, the curvatures of their corneal lenses, their precise location on the forehead and to what extent hairs on the insect head surrounding them affect their visual field. However, it has convincingly been shown that these eyes are incapable of forming an image on their respective retinas, because the images are always underfocused and would, at best, produce a very blurry representation of the real world. The retinas of the various ocelli in the different insect orders all contain typical insect photoreceptive cells with ultrastructurally similar membrane tubes that house the photopigments in them. The orientation and arrangement of the photoreceptive membranes, however, can vary between species, suggesting that some ocelli may be capable of perceiving linearly polarized light that could help them navigating. Yet again, this would not explain why not all flying insects share this ability and, in fact, why flying beetles do not even possess ocelli at all.

Can they perceive colours? I was perhaps one of the first in the world to test the spectral sensitivity of a dorsal ocellus of a bumble bee electrophysiologically and determined that it had two sensitivity peaks: one in the ultraviolet to light of around 350 nm wavelength and one in the green range of the spectrum around 520 nm wavelength. In terms of their visual field, I found that it covered an approximately 60 degree wide diameter. What I did not examine was the overlap between the visual field of the three ocelli with each other and the compound eyes. This was recently investigated by a group of researchers headed by Emily Baird in Sweden, who were interested why only in bumble bees but not in honey bees the three ocelli are placed in a horizontal row rather than being triangularly positioned and bumble bee males and females had similar eyes while in honey bees they were dissimilar.  The researchers found that the occluding hairs around the ocelli played an important role to reduce visual overlaps and that male bumble bees appeared to be foraging more like female bumble bees , while honey bee drones and female honey bees differed much more from each other. The data presented by the Swedish group allowed me to calculate an F-number that shows that the bumble bee’s dorsal ocelli could function under much dimmer light than humans could see in. And yet, as to the precise function of the little insect eyes, well, we still don’t know.

© Dr V.B. Meyer-Rochow and, 2021. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.

Ants and their guests

Of which some behave very badly

I met Bert Hölldobler in 1972 at the 14 th International Congress of Entomology in Canberra, the capital of Australia. He then told me he was appointed to be professor at Harvard University.  Harvard University! A PhD-student at that time, I was surprised that a man as young as Bert would be a Harvard University Prof, but reading his studies on ants, I was no longer surprised.

There is no other insect group than the 10,000 or so species of ants in terms of different social behaviours and lifestyles: Ants are social insects; solitary species do not exist. In the all-female populations (as in bees, males only need to fertilize a virgin queen; after that they can die) different castes varying in size and appearance have different functions. Although no ant species is marine, there is an intertidal one (Polyrhachis sokolova) and one that scavenges food from inside a pitcher plant’s insect trap (Camponotus schmitzi). Some species collect seeds or feed on other insects and small vertebrates; some clean carcasses of birds and mammals and army-ants are famous for their raids, separated by temporary bivouacs constructed by and with the ants’ own bodies. Honeypot ants have castes so round and heavy with honey that they can no longer move, while ‘aphid-tending’ ants protect (and ‘milk’) their aphids like cattle. Well-known are also weaver ants Oecophylla smaragdina (with nests of sewn-together leaves) and fungus-growing leafcutter ants. There, too, are at least 35 ant species that keep slaves of other species.

Anyhow, Hölldobler’s work that intrigued me most, dealt with unwanted beetle guests in ant nests; guests that behaved badly and had devious ways to sneak into an ant colony and not get removed. For the little antlike staphylinid beetle Atemeles to enter the nest of a Formica ant, it smells and behaves like an ant. Its larva possesses the same smell as an ant larva and for this reason remains unattacked. The beetle larva also knows how to beg for food and when it taps the mouth of a passing ant, the ant responds with regurgitating a drop of fluid, which the beetle larva ingests. The ants do not prevent the beetle larva killing and devouring the ants’ babies, but continue to feed the cheat. However, the beetle larvae’s disguise is so perfect that they themselves are in danger to be eaten by another beetle larva: these beetles are cannibals! At the end of summer the beetle larva pupates, yielding an adult beetle in autumn. The Formica host ant colony, however, stops reproducing in winter and the new beetle generation would starve  – unless, and that’s what they’re doing, they emigrate to find a nest of a Myrmica species that has eggs and larvae throughout the winter. To get into a Myrmica nest, the adult beetle secretes from its abdomen an appeasement fluid, which turns the Myrmica guards into drugged ‘friends’. Once inside the Myrmica nest the beetles have enough food, mature sexually and in spring bid good-bye to the Myrmica host and seek a Formica nest again to start a new generation.

There are even “highwaymen” beetle species that locate the ants’ foraging trails by scent and then ambush ant workers, tickle their mouthparts and steel what they spit out of what they had in their crops. Of course, harmless ‘tenants’ like some mites or springtails also exist in an ant nest; yet, I bet there are still many more species of the bad guys that await discovery. But it takes a lot of patience and good eyesight to spot them: believe me I looked for them and failed.

© Dr V.B. Meyer-Rochow and, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.