Love match

Sexual reproduction is almost a rule among animals, and mating between a male and a female is the initial step in it. But cases of parthenogenesis, budding, and scissiparity are also known among them. Parthenogenesis is common among insects, and even among such specialised insects as beetles. In case of snails, the two partners copulate mutually and both lay eggs, as either of them is provided with male as well as female gonads. A book was very famous during the war: "Die Sexualität" by Hartmann (1943). This book is entirely devoted to relative sexuality, mostly among Protozoa, where the size determines the sex, whether an individual will be a male or a female. The smaller one acts as a male. Homosexuality is known among many animals including beetles. A serious Hungarian journal (Rovart Lapok) had many years ago a paper entitled "About pederasty in beetles". It is a fact that people have very often recorded, among weevils, leaf-beetles, and scarabeids, interspecific matings, matings between males, between females, between larvae and adults, between nymphs and adults, etc. There are sometimes "normal" cases of mating between nymphs and adults among insects, as males do not wait for the complete emergence of the female from the skin of the penultimate instar. There is a show of urgency among competitors for such matings.

Mating among insects is extremely diverse and complicated. It is really aberrant among the bedbugs (Cimicidae), Nabidae, Corixidae, Anthoc-oridae and some other families of Heteroptera or bugs. Also, Strepsiptera, outside the Hemiptera, show an extra-genital insemination. It is the haemocoelian or traumatic mating (Carayon, in Usinger, 1966; Carayon,

1977). Among the Cimicidae, insemination is never effected by the usual genital route. The male punctures the body wall of the female with its aedeagus and injects an abundance of sperms into the female abdomen, but outside the usual reproductive tract. Insemination is thus extragenital and traumatic, because it starts with making of an integumental wound. There are, in connection with this behaviour, special structural differentiations, which together constitute the "paragenital system" (Carayon, 1977; Jolivet, 1991). A specialized organ exists in Cimex, Ribaga organ to facilitate the haemocoelian copulation. Among Nabidae and Anthoc-oridae, there is a tissue specially adapted to drive the spermatozoa through the blood to reach the oviducts. In Cimex, males never introduce their copulatory organs into the vagina of females. The male straddles the back of the female obliquely, his abdomen strongly incurved against the right side of his partner's abdomen, so that its extremity reaches not the orifice of the genital duct but that of the organ of Berlese, which is a special integumental pocket, where the penis penetrates and injects the sperms. Parts of the spermatozoa cross the walls of this pocket, and through the hemocoele some reach the seminal receptacle, and others penetrate directly into the ovarioles. Another part of the spermatozoa seems to be digested by the amoeboid cells in the pocket, and the products of the digestion would contribute to the development of the ovaries. Those amoeboid cells also secrete a hormone activating the spermatozoa (Poisson, in Grasse, 1951). The paragenital system and its accompanying behaviour are extraordinarily complex among Cimex and several other bug families. Afrocimex males, unable to distinguish the sexes, frequently mate between themselves, and, less often, inject mutually the sperm (Carayon, 1977). It is not infrequent to see two males copulating. Among Corixidae, sexual behaviour seems linked to the size of the partners, the smallest mounting the biggest. Lesbian Drosophila exist, and the gene for it seems recessive. Male and female bipotentiality in mating is known in Ceratitis capitata. In cages, its sexual bahaviour depends on various conditions, like sun, light, chemicals etc. It should be emphasised that homosexuality has been observed in all cases in breeding cages and under artificial conditions.

A question remains: what could be the utility or the finality of this aberrant homosexual behaviour of the Cimicidae? According to a friend entomologist, this mating system would prevent a too big consanguinity (i.e. close inbreeding) in a restricted area, like a room. Two males copulating would mix up their spermatozoa in the hemocoele and the mixed sperms would be so reinjected to a female which would get that way a greater variety of gametes. The idea seems rather far-fetched, and it would be necessary to see if a male, so "fertilized" by another male, is capable of reinjecting, partly at least, into a female, the spermatozoa of another male.

In many insects there may be a violent conflict among competing males for a female for a successful mating. The size of the horns of a horned beetle gives them sometimes an advantage in the fight. Horny leaf beetles use them to fight, but hornless ones, such as the Colorado potato beetle and Gastrophysa viridula, also fight vigorously to get a female, and, when they get hold of one, the winner stays around to protect her.

Pseudocopulatory behaviour is known among the females of a weevil, Otiorhynchus pupillatus. A parthenogenetic female of this species, when ready to oviposit, searches actively another female and mates with it.

Some insects remain coupled all their life. An example is the love-bug, Pleaa nearctica, in North America. Since 1965, this fly (Diptera, Bibionidae) has invaded Florida, from Mexico, and population explosions are known twice a year, in May and September. The flies are harmless, but they adhere to the windshield of cars during driving. Many times PJ was obliged to stop and to clean his windshield. Flight of the flies has been encountered by light airplanes at altitudes up to 500 m. Each female lays more than 300 eggs in decaying vegetation. Spattered remains of these insects can damage the car by clogging the radiators (Hetrick, 1970; Denmark and Mead, 1992). The small flies get crashed like scrambled eggs and the mixture slightly damages the paint on vehicles. The mating flies do not separate and remain connected for life.

More than two sexes have been recently attributed to some American ants. That fits science fiction where authors always try to invent new ways of reproduction on their ghosty planets. It has recently been found that certain ants of the genus Pogonomyrmex seem to possess three or four sexes: the queen must copulate first with a male of her proper genetic group to produce queens, and then with males of another genetic group to produce workers and soldiers (Parker, 2004). Caste differentiation in Pogonomyrmex ants is very complicated and results also from environmentally induced differences in gene expression (Gahan and Keller, 2003). Genetic basis is advocated for queen-worker dimorphism of Pogonomyrmex and this mode of caste determination has consequences in multiple mating by females for control of sex ratio (Volny and Gordon, 2002). Among other ants, the castes seem to be determined by environmental or nutritional factors. Certain fungi show some hundred different types of reproduction, but Pogonomyrmex is the only example known in the animal kingdom.

Many hymenopterans, in the temperate and tropical world, do make love with flowers. In Australia ants show this phenomenon, and we know how infrequently ants pollinate flowers. The fact was discovered in 1916, in Algeria, but has been restudied in detail by Kullenberg (Kullenberg, 1961) and the Scandinavian school after 1961 (Kullenberg and Bergstrom, 1976). Several orchids, without nectar, oil, or edible tissue, have got transformed into prostitutes, and have mimed morphologically and chemically an insect female, and thus have succeeded to get pollinated by various hymenopterans. Practically, in such cases a male insect masturbates itself on flowers. The fact was discovered among Ophrys species, which are European and mediterranean orchids, and which possess a labellum recalling by its shape, its colour, its velvetiness, an insect body. Similar cases have been found among the Australian Cryptostylis, the Neotropical Paragymnomma and several others. There are certainly many other examples over the planet awaiting a detailed study. These orchids are visited by wasps, flies, bees, ants, and several other insects, which also take care of the pollination in addition to their sexual satisfaction.

An opposite situation: the English Ophrys apifera pollinates itself, its own pollen gets the pistil fertilised, since it has lost its pollinator or its "sexual" partner through extinction.

The strange resemblance between the insect and the flower was already seen in 1831. Mating between insect and flower takes place generally with newly hatched males when the females are still uncommon.

In North Africa, it is Scolia ciliata, a wasp which pollinates Ophrys speculum during pseudo-copulation. In Northern Europe, Ophrys muscifera is pollinated by two species of wasps of the genus Gorytes. In the mediterranean region, several Ophrys species are pollinated by various hymenopteran insects, Scolia, Eucera and Andrena. Kullenberg has recorded bigeneric attractions of Ophrys scolopax, in Lebanon, which attracts Eucera and Andrena males. To facilitate the copulation, the labellum of the flower is relatively strong and the epidermal cells have very strong walls. The primary stimulation is essentially olfactory, and is followed by tactile and visual stimulations, the last one less important (Jolivet, 1998).

It is a fact that for a non-initiated insect male, the flower morphology of an Ophrys flower is close to the shape of an insect, mostly a hymenopteran, with pseudo-eyes, pseudo-antennae, and pseudo-wings, as well as with hairs similar in shape, colour, odour and texture to the ones of an insect female. A layman, with little experience, may behave as a finalist. Bernardin de Saint Pierre, an extreme eighteenth century finalist, maintained that if a melon had ribs, it was to be eaten in a family. La Fontaine, the fabulist but also another finalist, said, in one of his fables, that if a pumpkin was growing on the ground and acorns on a tree, that was to prevent them doing any harm in falling on living beings. La Fontaine did not know that there was a pumpkin tree (Dendrosicyos socotrana), the only cucurbitaceous tree, in Aldabra Island. These analogies have been mentioned to point out how an inexperienced individual may be confused. That is how an uninitiated male takes an orchid, with only a rough resemblance of a female, for its mating partner.

The insect seems mainly attracted by the odour, similar to the female of its own species. The plant secretes a real mimetic pheromone. This smell is so powerful that the males look for a flower, even wrapped in a paper. It has even been seen that, at least in one case, the males preferred the flower to their own females.

In addition to flower morphology and the odour it produces, there seems to be another factor for attracting male insects. To compensate for its immobility, the labellum, where lands the insect, is dark purple with clear marks and spots, mirror-like reflecting the UV rays. Among some flowers, the labellum moves also slightly with the wind.

Once landed on the orchid labellum, the insect finds the hairy curves, the projections, the hairs, which seem to persuade him to believe that he has really found the soul mate, and he immediately enters in pseudo-

copulation with length and vigour. The copulating organ is protruded and driven into the velvety parts of the labellum. The males, excited by the smell, may sometimes be seen fighting for the possession of a flower. However, the orchid does not seem comfortable with its loving partner, and though the penis is out and rubbed continuously, there seems to be no ejaculation at least in Ophrys. Sperms have been detected once on Cryptostylis, an Australian orchid, pollinated by ichneumonids.

Orchids have sometimes, for attraction of insects, extra-floral nectaries on the pedicels, the bracts or on the petioles. Their flowers are generally entomophile and pollination is done generally by bees and wasps, very little by beetles and very exceptionally by ants. Pseudocopulation is extremely rare among them. Examples are the cases of Microtis parviflora in Southern Australia or Leporella fimbriata, also in Australia (Peakall, 1989; Peakall et al, 1987). Seeds are also exclusively anemophilic. Leporella is exclusively pollinated by the flying males of Myrmecia urens. Janzen once mentioned the extreme rarity of the plant pollination by ants, assuming that these insects were wingless (workers), that they possessed metapleural glands, which were pollen killing. As is true for many other Hymenoptera, such as Scolia, Andrena, Gorytes, Eucera and many others, the ant male also shows a real pseudo-copulation with the flower, resembling a smelly female, but without nectar. In the case of Leporella, an extraordinary case, the ant male lacks in metapleural glands, which in other ants are meant to destroy pollen (Jolivet, 1996). It was known that sometimes flies pollinate orchids. A recent paper (Blanco and Barboza, 2005) mentions a pseudocopulation in Lepanthes glicensteinii, an orchid from Costa-Rica, by fungus gnats (Bradysia floribunda, Diptera: Sciaridae). The species has a minuscule labellum adapted to the pollinator. The fly appears to ejaculate during pseudocopulation.

As was written by A. Huxley, "even so, the insect flies, full of hope from flower to flower, do again the semblance of copulation, and, we can hope, takes pleasure, but, with much efficacy, carries the pollen". It also happens that sometimes the labellum is violently bitten during the operation.

The copulating orchids vary very much in shape and pilosity according to their copulation partners in their geographical area, and in their botanical species. Ophrys lutea produces an inverted copulation because of its floral structure.

Anyhow, this "sexual" adaptation between a flower, lacking in any other device for attracting a pollinator, and an insect, which does not get any reward for its action, but for assumed sexual satisfaction, is extremely interesting. It must have been the result of a long evolution from a formerly nectariferous plant ancestor. For such orchids, this "sexual" solution seems their only chance of survival after losing their nectaries, since autopollination is not a desirable alternative.

References

Blanco, M. A. and Barboza, G. 2005. Pseudocopulatory pollination in Lepanthes

(Orchidaceae: Pleurothallidinae) by fungus gnats. Annals of Botany 95: 763-772. Carayon, J. 1977. Insémination extra-génitale traumatique. In: P. P. Grassé, Traité de

Zoologie, Masson publs., Paris. 8 (5 A): 351-390. Denmark, H. A. and Mead, F. W 1992. Lovebug, Plecia nearctica Hardy (Diptera:

Bibionidae). Entomology Circular, DPI, Gainesville, FL 102: 1-8. Gahan, S. H. and Keller, L. 2003. Complex hybrid origin of genetic caste determination in harvester ants. Nature 424: 306-309. Grassé, P. P. 1951. Traité de Zoologie. 10 (2). Masson publs., Paris: 1657-1803. Hartmann, M. 1943. Die Sexualität. Gustav Fisher, Iena.

Hetrick, L. A. 1970. The "love-bug", Plecia nearctica Hardy (Diptera: Bibionidae).

Entomology Circular # 102, Gainesville, FL. 2 pp. Jolivet, P. 1991. Curiosités Entomologiques. Chabaud publs., Paris: 170 pp. Jolivet, P. 1996. Ants and Plants. An example of Coevolution. Backhuys Publs., Leiden.

Jolivet, P. 1998. Interrelationships between Insects and Plants. CRC Press, Boca Raton, USA.

Kullenberg, B. 1961. Studies on Ophrys Pollination. Almguist Wiksell, Upsala. Kullenberg, B. and Bergstrom, G. 1976. The pollination of Ophtrys orchids. Bot. Not. 129 (1): 11-19.

Parker, J. D. 2004. A major evolutionary transition to more than two sexes? Trends in Ecology and Evolution 19 (2): 83-86. Peakall, R. 1989. Pollination of Leporellafimbriata, the only pseudocopulatory orchid known to mimic female ants. Symp. Ants Plants, Oxford: 32. Peakall, R., Beattie, A. J. and James, S. H. 1987. Pseudocopulation of an orchid by male ants: A test of two hypotheses accounting for the rarity of ant pollination. Oecologia 73 (4): 522-524. Usinger, R. L. 1966. Monograph of Cimicidae (Hemiptera-Heteroptera). The Thomas Say Foundation. 7. Entomological Society of America. College Park, Maryland: 81-166.

Volny, V P. and Gordon, D. M. 2002. Genetic basis for queen-worker dimorphism in a social insect. PNAS 99 (9): 6108-6111.

— Fig. 26.1. Mating pair of Plecia nearctica (Diptera: Bibionidae); female on right. 13-15 mm. Florida.

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