Damselflies experts in ballistics

During the Carboniferous (about 236 mya), there were giant dragonflies, or more exactly enormous species, to some extent related to the typical Odonata. The big Meganeura monyi was described by Brogniart in 1884; it measured more than 70 cm in wingspan. Carpenter (1992) places it under the Protodonata. Such a big insect had no predators, and probably was a great destructor of the already rich insect fauna, flying in the primitive forests, composed mostly of Ginkgoales, Equisetales, arborescent ferns, Lepidodendron and Sigillaria. Cycadales appeared in abundance later during the Mesozoic, and real flowering plants were absent until the Trias, when they appeared in very primitive forms, to evolve further during the Cretaceous. Those big Odonata-like insects disappeared during the Permian. There is no insect even now so big as Protodonata on our planet. The biggest moths Thysania agrippina, have a wingspan of 230 to 305 mm, Attacus atas of 160-300 mm, and the longest phasmids in New Guinea are less than 400 mm. Two species of Epiophlebia from Japan and India have Mesozoic characters, combining the characteristics of both suborders, the dragonflies and the damselflies, but their size is average (Asahina, 1950, 1954).

There are, however, in South Africa and in Amazonia very big damselflies, which seem directly surviving from the prehistory, when you see them flying. PJ saw them often in Brazil. They belong to the Pseudostigmatidae in America and to the Megapodagrionidae in South Africa, Tanzania and Madagascar, families placed among the Zygoptera, i.e. the damselflies, a suborder under Odonata. They are delicate forms with forewings and hindwings similar, with the wing base narrow and petiolated. The larvae of Mecistogaster modestus breed in the water accumulated in the leaves of epiphytic bromeliads; others (Microstigma sp.) in the water of Bertholletia pods, fallen on the forest floor. The long abdomen of the females of Mecistogaster has been regarded as an adaptation for penetrating deeply into leaf axils of bromeliads during oviposition (Calvert, 1911). The argument does not explain why male abdomens should be longer than those of females (Fincke, 1984). Young (1980, 1981) has studied the biology of Megaloprepus coerulatus in Costa Rica.

Normally Odonata eggs are laid close to the surface of water bodies, permanent or not. Many Zygoptera and a few Anisoptera (dragonflies) families insert their eggs into tissues of plants growing near or in water. Some Anisoptera attach their eggs to plant leaves or stems, but most of the genera lay their eggs in open water. The colour of these eggs is generally white or greyish, and can change to brown or dark grey later on. Among tropical species the eggs can be brilliantly coloured as blue, green, pink, and also change colour later. Most of the species from the two suborders, mentioned above, lay their eggs in phytotelmata, the natural reservoirs on tropical plants, such as tree holes, wrapped leaves of banana plants, Heliconia or epiphytic Bromeliaceae, etc. Those natural aquaria, often suspended on the trees, contain an abundant plant and animal life, including many insects: Odonata larvae, larvae of Diptera, belonging to many families, including chironomids, mosquitoes, Tipulidae, beetles, including Helodidae and Hispinae (like Cephaloleia in Heliconia water-filled bracts, Jolivet and Verma, 2002), Oligochaeta worms etc.; they devour each other voraciously. Frogs even sometimes join the group, but water bugs like Belostomatidae are missing. It seems, however, that dragonfly larvae eat each other, and they also devour rapidly the predator of mosquito larvae, Toxorynchites, to the great displeasure of the medical entomologists. But Odonata larvae in general help in mosquito control.

Forty-seven species of Odonata seem specific for breeding to phytotel-mata, and among them only a few species, including some big Zygoptera, have been observed breeding in tree holes, for instance, one in Africa, one in Australia and one in the neotropical region. These big tropical damselflies, flying slowly and delicately, however show some punctual interruptions, like when capturing spiders or their preys, already wrapped into the net. This behaviour is different from that of most of the dragonflies or damselflies, which catch their prey when flying. Really very little is known of the behaviour of those big insects, and very few observations have been made in the tropics.

While the long wingspan is important among those big species, the abdomen is also very long, sometimes longer for the male (Mecistogaster linearis). The meaning of this lengthening of the abdomen has remained for long a mystery. It has been suggested that those long abdomens allow the females to deposit their eggs through the narrow openings of the water-tanks of Bromeliaceae, since to penetrate inside treehole or phy-totelmata remains a very risky venture for a dragonfly, because a vertebrate predator, a toad, for instance, may be hidden inside. Moreover, the distribution of tree holes and phytotelmata through the forest requires a difficult search by the female of the damselfly. Sometimes, the males protect those holes against the trespassers, rival males for instance, and allow only the females with whom they had copulated, to lay eggs inside the holes. The larval habits of Mecistogaster modestus have been well known. It has been suggested that the unusually long abdomen of the adult is functionally correlated with the need to place the eggs in or near the water contained at the base of the bromeliad leaf (Corbet, 1983). However, this explanation is not fully satisfying, because, as has been pointed out before, it does not account for extra long abdomen in males. Fincke (1984, 1992) has reported the female's behaviour in searching for treeholes in Panama, and the behaviour varies much with species.

What is the use of the long abdomen in the large odonatans? It seems that Machado and Martinez (1982) have solved the problem, at least for one treehole breeding Bolivian species, Mecistogaster jocaste. The female of this species hovers above a tree hole and makes jerky movements with the curved abdomen, then she throws individual eggs at the water surface in the direction of the shaded area underneath the roof of a hole. The abdomen never touches the water, and the yellow eggs, after drifting horizontally, remain floating. The female always oviposits unattended by the male. Egg throwing for Mecistogaster is different from egg-dropping in several genera. It is probable that the system is efficient because of the extended abdomen. To be able to throw the eggs inside holes, a long abdomen is more useful; the longer it is, the greater would be the velocity of the egg at the time of its ejection. Roughly, the main advantage is to introduce the eggs into water contained in a deep hole with a small opening, without taking any risk for the female itself. The oviposition procedure of other big damselflies is not well known. It is probable that if some of them throw their eggs, others drop them only when in flight. Many Zygoptera lay eggs in aquatic plants (peduncles, leaves, stems). The egg development is endophytic. A North American damselfly, Enallagma hageni, is one of the species, the females of which submerge themselves completely before inserting their eggs into plant tissues (Fincke, 1985; Preston-Mafham et al, 1993). Probably Megalo-prepus coerulatus does oviposition by egg-throwing, but that remains to be verified (Young, 1980, 1981).

Machado has used mathematics to study the kinetic energy imparted to the egg by the length of the abdomen, and to study the parabolic pathways taken by the egg towards the surface of water. It has been inferred that a damselfly has to aim straight, and that the giant Odonata are experts in ballistics. The longer the abdomen, the higher the velocity of the egg at the moment of ejection. It is likely that the African

— Fig. 27.1. Mecistogaster jocaste female, a Bolivian damselfly, throwing its eggs inside a treehole full of water (after Machado and Martinez, 1982).

— Fig. 27.1. Mecistogaster jocaste female, a Bolivian damselfly, throwing its eggs inside a treehole full of water (after Machado and Martinez, 1982).

megapodagrionid, Coryphagrion grandis, lays its eggs through a strong ejection and perhaps also the Australian species, Podopteryx selysi, and the neotropical, Megaloprepus coerulatus. All are treehole breeders. P. selysi with 90 mm wingspan is the largest damselfly of Australia. However, the biology varies so much that no generalisations may be made before many more studies have been done on their habits and ways of life.

Recent papers (Uhia and Cordero Rivera, 2005) have shown that mating process is not simple among Odonata, particularily among damselflies. In Odonata, males remove sperm during copulation from the spermatheca or the bursa copulatrix. Sperm competition and cryptic female choice are both involved. More attention should be devoted on egg laying or throwing, mostly in the tropics.

References

Asahina, S. 1950. On the life-history of Epiophlebia superstes (Odonata, Anisozygoptera). Proc. 8th int. Congr. Ent.: 337-341.

Asahina, S. 1954. A Morphological Study of a Relic Dragonfly Epiophlebia superstes. Jap. Soc. Promotion Sci., Tokyo: 153 pp.

Calvert, P. P. 1911. Studies on Costa Rica Odonata.II. The habits of the plant-dwelling larva of Mecistogaster modestus. Ent. News. 22: 402-411.

Carpenter, F. M. 1992. Arthropoda 4. vol. 3. Superclass Hexapoda. In: Treatise on Invertebrate Paleontology. The Geological Society of America, Boulder, Colorado: 277 pp.

CORBET, P. S. 1983. Odonata in phytotelmata. In: J. H. Frank and L. P. Lounibos (eds.) Phytotelmata. World Natural History Publications ( Plexus), Marlton, N. J., USA: 29- 54.

Fincke, O. M. 1984. Giant damselflies in a tropical forest: reproductive biology of Megaloprepus coerulatus with notes on Mecistogaster (Zygoptera: Pseudostigmatidae). Adv. Odonatol. 2: 13-27.

Fincke, O. M. 1985. Alternative mate-finding tactics in a nonterritorial damselfly (Odonata: Coenagrionidae). Anim. Behav. 33: 1124-1137.

Fincke, O. M. 1992. Behavioural ecology of the Giant Damselflies of Barro Colorado island, Panama (Odonata: Zygoptera: Pseudotigmatidae). In D. Quintero and A. Aiello: Insects of Panama and Mesoamerica. Selected Studies: 102-113.

Jolivet, P. and Verma, K. K., 2002. Biology of Leaf Beetles. Intercept, U.K.: 332 pp.

Machado, A. B. M. and Martinez, A. 1982. Oviposition by egg-throwing in a

Zygopteran, Mecistogaster jocaste Hagen, 1869 (Pseudostigmatidae). Odonatologica 11 (1): 15-22.

Presto-Mafham, R. A. and K G. 1993. The Encyclopedia of Land Invertebrate Behaviour. The MIT Press, Cambridge, Mass. USA: 320 pp.

Uhia, E. and Cordero Rivera, A. 2005. Male damselflies detect female mating status: importance for postcopulatory sexual selection. Animal Behaviour 69: 797-804.

Young, A. M. 1980. Feeding and oviposition on the giant damselfly (Megaloprepus coerulatus (Drury) ) in Costa Rica. Biotropica 12: 237-239.

Young, A. M. 1981. Notes on the oviposition microhabitat of the giant damselfly Megaloprepus coerulatus (Drury) (Zygoptera: Pseudostigmatidae). Tombo 23: 17-21.

0 0

Post a comment