Biting Midges

An industrious hadrosaur stripped foliage from a kauri tree sapling growing at the border of a sodden meadow. Metallic-colored dragonflies greeted the day by darting across the tops of ferns and horsetails and catching small insects on the wing. Clouds of silvery-winged mayflies fluttered up from the dew-covered vegetation. The dinosaur munched away at overhanging branches, consuming myriads of aphids and scale insects that covered the leaves. The commotion caused small weevils and xyelid sawflies to drop to the ground, where they unfortunately encountered beetle-shaped scavenging cockroaches. Primitive katydids and walking sticks escaped the encroaching teeth by fleeing to quieter areas of the tree.

This idyllic scene was soon disrupted by a group of hungry biting midges that had been resting on some nearby reeds. Rising into the air like a puff of dark smoke, they headed with bloodthirsty determination straight for the pebbly skin of the feeding animal. The jabs of sharp pain felt by the browsing hadrosaur several moments after they alighted were probably ignored. The voracious insects took about two to three minutes to fill their stomachs with blood, and then rested briefly before returning to the reeds. The females had obtained their goal, a source of protein, and would soon lay their eggs in moist soil at the edge of a swamp. Their bites were not innocuous because their victim may well have been infected by microscopic parasites that would take its life. Only time would tell.

Biting midges (ceratopogonids) were just one of many insects that fed on vertebrate blood in the late Mesozoic. From amber, we know they shared this habit with sand flies and corethrellid flies,338 as well as other groups found in different types of fossil deposits (color plate 11C). Some people may be familiar with biting midges as the minute "no-see-ums" or "punkies" that deliver painful bites. You may not notice them coming or going— but you definitely know when they begin to feed! These ancient flies were quite common and widely distributed throughout the Cretaceous.13156 Their evolutionary success is due to their broad host range, which includes taking blood from insects, fish, amphibians, reptiles, birds, and mammals. But they also have adapted to many different habitats that can support their larvae, from aquatic (lakes, streams, tree holes) to moist (decaying plant material, dung) and even semiarid (sand).157,158 We can say with a high degree of confidence that the developmental sites of Cretaceous biting midges probably included dinosaur dung.

With such a wide range of available food sources, how do we know if a fossil biting midge could have fed on dinosaurs? Fortunately there are some morphological features that directly tie them to a specific feeding behavior. Those that feed on vertebrates (color plates 9A, 9B) tend to have finely serrated mandibles, retrose (downward pointing) teeth on their maxillae, and small tarsal claws, while invertebrate feeders generally have coarsely serrated mandibles, maxillae without retrose teeth, and large tarsal claws. Additional characters also provide clues as to what type of vertebrates are attacked, such as whether they are warm-or cold-blooded, birds or mammals, and even their relative size. An analysis of these characters on Cretaceous biting midges indicated that several genera and species dined on large vertebrates, which certainly included dinosaurs.51

Those that relished dinosaur blood could have been related to biting midges that currently feeds on lizards160,161 or attack turtles and iguanas. A leptoconopid midge searches out several species of California sand-dune lizards on cool early mornings.160 Once they insert their mouthparts and start engorging, they are almost impossible to remove, even when the lizard crawls through the sand. These biters belong to an ancient lineage that probably attacked dinosaurs.

The onslaughts of ceratopogonids on sea turtles commence as soon as the reptiles arrive on land and continue until they reenter the sea.162,163 In fact, these cunning insects seem to anticipate their host's arrival! They gather in groups of seven or eight and over a hundred individuals will dine on a single turtle during the forty-minute period it is out of the water. This association between biting midges and sea turtles along Central American beaches is probably quite ancient because the insect's distribution coincides with the nesting sites of the leatherback turtle. There appears to be a decided preference for these marine reptiles, since as long as they are present, humans and dogs are not bitten.

Did dinosaurs have allergic responses to biting midges? Many humans experience several types of reactions to these biters. Aside from the initial searing pain, there can be a response to their saliva, expressed as a tender swelling around the wound. In sensitized individuals, itching blisters can leak fluid for two to three days and scratching can cause bacterial and fungal infections, which without treatment could become life-threatening.157

Since biting midges are so minuscule (color plates 9A, 9B), what part of the dinosaur would they attack? These insects search for a highly vascularized area of the epidermis. In elephants, this region occurs behind the ears.158 The skin between the tubercles would be the natural point of attack, and even if some dinosaurs were covered with feathers, the surface between the quill insertions would provide adequate feeding sites. Cer-atopogonids are pool feeders157 and all they require is an area of thin skin with some capillaries close to the surface. As soon as blood fills their small trough, they begin dining. Some may have favored the area around dinosaurs' eyes like the site chosen by the present-day human biter, Austroconops.51,166

If one of the no-see-ums that gorged on a dinosaur contained stages of Cretaceous malarial parasites, such as Paleohaemoproteus (figs. 23, 38),167 the microorganisms could have been transferred into the vertebrate's bloodstream. At first, the dinosaur may have felt no ill effects. However after the protozoa began to

Figure 23. A Cretaceous biting midge (Protoculicoides sp.) carrying a malarial parasite (Paleohaemoproteus burmacis)167 is feeding on the exposed skin between the scales of a dinosaur. Top, stages of the parasite that occur in the biting midge: A. Spheroid bodies destined to become sporozoites developing in an oocyst attached to the gut wall. B. Immature sporozoites developing in the oocyst. C. Mature elongate sporo-zoites leaving the oocyst and migrating through the vector's body to the salivary glands. Bottom, stages of the parasite that occur in the dinosaur: D. Elongate sporo-zoites enter cells of internal organs and produce small, spherical asexual bodies called merozoites. E. One merozoite enters a blood cell while another has already begun development into a gametocyst. F. A mature gametocyst nearly fills a blood cell. This is the stage acquired by the biting midge while feeding. Sexual reproduction of the parasite occurs in the insect's gut, and the product of the union (ookinete) enters the gut wall and develops into an oocyst. Continue the parasite cycle by going back to A. Dark oval objects in the vertebrate cells are nuclei. Not drawn to scale.

Figure 23. A Cretaceous biting midge (Protoculicoides sp.) carrying a malarial parasite (Paleohaemoproteus burmacis)167 is feeding on the exposed skin between the scales of a dinosaur. Top, stages of the parasite that occur in the biting midge: A. Spheroid bodies destined to become sporozoites developing in an oocyst attached to the gut wall. B. Immature sporozoites developing in the oocyst. C. Mature elongate sporo-zoites leaving the oocyst and migrating through the vector's body to the salivary glands. Bottom, stages of the parasite that occur in the dinosaur: D. Elongate sporo-zoites enter cells of internal organs and produce small, spherical asexual bodies called merozoites. E. One merozoite enters a blood cell while another has already begun development into a gametocyst. F. A mature gametocyst nearly fills a blood cell. This is the stage acquired by the biting midge while feeding. Sexual reproduction of the parasite occurs in the insect's gut, and the product of the union (ookinete) enters the gut wall and develops into an oocyst. Continue the parasite cycle by going back to A. Dark oval objects in the vertebrate cells are nuclei. Not drawn to scale.

multiply, she could have suffered anemia, weight loss, and possibly death. It would not have mattered whether she was warm- or cold-blooded since this type of malaria develops in a wide range of birds and reptiles today157168-170 and vectors were present throughout the Cretaceous.156164

Another punkie may have been infected with vertebrate pathogenic viruses. Numerous viruses in the family Reoviridae are transmitted to mammals and birds today by ceratopogonids.157 One that causes bluetongue disease (an Orbivirus) is highly lethal in ruminants and has caused the deaths of over a million sheep in Europe since 1998.165 Other ceratopogonid-transmitted re-oviruses cause lethal diseases in horses and infect wallabies and kangaroos.171 Burmese amber biting midges were infected with reoviruses (color plates 9C, 9D), so these pathogens were certainly present by the mid-Cretaceous.172

These flies are also capable of vectoring other kinds of viruses to birds and mammals. One, a rhabdovirus, causes bovine ephemeral fever and several related diseases of cattle in Africa, Asia, and Australia.164 There is even a report incriminating a biting midge in transmitting the Charleville rhabdovirus to reptiles in Australia,171 and no-see-ums also carry viruses in the family Bunyaviridae to rabbits and ungulates.157

From the above accounts, it is obvious that these minute insects are important vectors of arboviruses (arthropod-borne), and since at least one type of reovirus is known from the mid-Cretaceous, others could have been infecting dinosaurs.

Biting midges also disseminate filarial nematodes similar to one that causes a widespread skin condition in monkeys, the great apes, and humans in Africa and South America.157 The roundworms responsible occur in the subcutaneous tissues and body cavity. Human infections were probably acquired by midges feeding on both men and primates because the nema-todes in these hosts are closely related.173 Ceratopogonids also transmit filarial nematodes (Splendidofilaria) to magpies and quail in North America. In both cases, the parasites lodge in the wall of the bird's aorta.173

Since biting midges are cosmopolitan, occur in many different habitats, and feed on all groups of vertebrates, their potential role in disseminating diseases in the Cretaceous could have been quite significant. While they are small and have a limited flight range, winds can carry infected individuals over long distances, possibly as much as a hundred miles in a single night.165 In the case of African horsesickness disease, winds carried infected midges from Africa to the Middle East, Cyprus, and Turkey.157

Some ceratopogonids would have sought their victims during the day, especially in the early morning or late afternoon just before sunset. Others would have fed at twilight and/or at night. The biting cycles were probably linked to the activity of their preferred hosts. Since these insects are active in subtropical and tropical areas throughout the year, there would have been little respite for the dinosaurs.

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