Parental care in insects

Parental care, as seen in mammals, specially in man, has little to compare with in insects. But some different protection strategies for progeny are seen among insects. After all, survival of offspring for continuity of the race is an important factor in their selection too.

One simple offspring protection strategy among insects is production of a large number of eggs, so that at least some complete their development and reach adulthood. Many insects show high fecundity, a single female producing hundreds to a few thousand eggs in her life time. Many insects, for example some leaf beetles (Family Chrysomel-idae), lay eggs in the form of aggregates or egg clusters. Timarcha (Chrysomelinae) glues their eggs together to form an aggregate, using their secretions. Eggs, laid in groups, have defensive value in several different ways, namely:

(i) If eggs are in an aggregate, some of them are able to survive a parasitic attack, either because some eggs in the mass are shielded by others, or because the attacking parasite has a limited egg laying capacity. It has been observed by Becker and Frieiro-Costa (1988) that some eggs in an egg collection in an ootheca of a tortoise beetle remain unparasitised.

(ii) In some insects the female provides a protective cover for laid eggs, or an ootheca. If eggs are in an aggregate, a single ootheca affords protection to a number of eggs, and the mother is able to provide the protection to several eggs in a single operation.

(iii) In some species, larvae are gregarious, and they take to a group defence strategy, like round defence or cycloalexy (see the chapter on "Round defence"). If eggs are in an aggregate, formation of a larval group is facilitated.

(iv) In some New World tortoise beetles (Family Chrysomelidae, Subfamily Cassidinae) the mother remains close to her developing progeny, protecting them. Laying eggs in a group helps to make parental care available to a number of developing individuals at the same time.

The ootheca, or the protective cover around eggs provided by the mother, is made up mainly of a hardened secretion from some glands associated with the last part of the oviduct in the mother. It may be a simple parchment-like dome around one or a few eggs, or it may be a complex structure, enclosing a fairly large number of eggs, as in case of mantids and some tortoise beetles. The ootheca of the tortoise beetle Aspidomor-pha miliaris is a series of parchment like leaflets, arranged serially, partly fused at the edges, and enclosing between them several transverse rows of four eggs each (Kalaichelvan and Verma, 2002).

Many tortoise beetles make a simple ootheca, enclosing one or a few eggs, and place over it a fecal discharge. The fecal deposit not only conceals the eggs, it is believed that it also provides physical and chemical protection to them (Kalaichelvan and Verma, 2000). As has been said in the chapter "Chemical defence in beetles and moths", the fecal discharge may be mixed up with toxic secretion of some exocrine glands, or some toxic compounds, present in mother's food, may have passed out with the fecal discharge.

Golden eyes (neuropterous family Chrysopidae) have taken to a peculiar way to protect their eggs. The eggs are attached to long, slender and flexible stalks, and may be laid singly or in groups. The stalks readily bend, and thus the eggs are difficult to reach by a parasite or a predator. A similar egg protection strategy is seen in some tortoise beetles, e.g. Chelymorpha and Omaspides (Olmstead, 1996) and also in some Clytrinae, a chrysomelid subfamily.

Generally insects lay their eggs on or close to the food of the future larvae, e.g. on leaves, stems, grains etc.. In this context specially notable is the case of ambrosia beetles (Family Platypodidae). The wood boring female of these beetles makes a burrow in a tree trunk or a freshly fallen log, extending deep into the sap wood. She releases from a special pocket on her thorax spores of a fungus. The fungus grows on walls of the burrow, and stains them black. The tunnel has side pouches or "niches". One egg is laid in each "niche". Larvae, on hatching, feed on the fungus. Such special care for providing food to their larvae appears to have evolved independently in nearly a dozen of families, especially those that exploit decomposing wood, dung or fungus (e.g. in Passalidae, Platypo-didae, Scolytidae, Erotylidae, Tenebrionidae, Staphylinidae, Silphidae, Scarabeidae). Hydrophilidae and Chrysomelidae, not specially connected with dung, wood and fungus, show also, among some subfamiles and genera, maternal care.

Some solitary wasps (hymenopterous families Sphecidae and Eumenidae) make mud nests on rocks, walls of buildings and trees. They provision their nests, before egg laying and sealing of the nest, so that their larvae on hatching find themselves surrounded with food. The provision in the mud nest is stung and paralysed spiders in case sphecid wasps, and paralysed caterpillars in nests of eumenid wasps.

Maximum parental care is seen among social insects (ants, bees, wasps and termites). Their developmental stages are lodged in the nest of the colony, taken care of by constant presence of adults, and their larvae are given regular feed by workers, which also actively defend and protect the colony.

In some tortoise beetles of South America the female, after laying her eggs in a cluster, remains close to them and to the resulting larvae and pupae, actively defending them against predators, like ants. This association between parents and their offspring has been referred to as "subsociality" (Wilson, 1971; Jolivet, 1988, 1997; Windsor and Choe, 1994), as it shows one significant feature of the typical insect social life, namely presence of adults around the developmental stages, throughout their development, to protect them. Windsor and Choe (1994) tried to make out a parallel between classification of and maternal care among South American Cassidinae. Membracid bugs (Homoptera) and many other insects maintain feeding aggregations of adults and developing offspring, until the latter reach adulthood. In case of the membracids, the presence of ants adds to the protection of the eggs and then of the offspring. Recently, Lin et al. (2004) tried to compare phylogenetics with evolution of maternal care among membracine treehoppers. They conclude that there is a strong phylogenetic component in the evolution of the subsociality of the bugs. In some cases, among some rare insects, the male parent remains close to the female and the progeny, apparently helping the female to protect the latter. Some female fungus beetles, like Pselaphicus giganteus (Erotylidae) in Trinidad, gather their young larvae into a pile before going in search for a fungus for them to eat (Preston-Mafham et al, 1993). It is rather strange that subsociality seems confined to cassidines only in tropical America. Guarding can last three to four weeks in some American cassidines. Among Chrysomelinae, some species of Gonioctena show in the Palaearctic Region larval cycloalexy combined with maternal care, and sometimes also ovoviviparity (Kudo and Hasega-wa, 2003). In Labidomera suturella, another chrysomeline, females in CostaRica exhibit guarding their larvae by their presence (Choe, 1989). Platyphora in tropical America lay eggs or larvae according to the species. They are brightly colored and very toxic. The larvae generally go on cycloalexy, but the parents do not seem to watch them.

It is paternal care in some water bugs, as male carries the eggs on its back, and also in a spider-hunting wasp, Trypoxylon superbum, in which male remains close to its nest to guard its progeny against parasitoids and ants. Some male assasin bugs in Africa (Reduviidae) guard the eggs, and protect them from parasitoids. Pelissier Scot (in Resh and Carde, 2003), mentions, as an advanced paternal care, in the cases of the arctiid moth, Utetheisa ornatrix, and in some katydids, in which the male transfers toxins to the female during mating, so that the eggs, laid by the female, are toxic. Paternal care was once suspected in some cycloalexic tortoise-beetles of South America, but has never been proved.

Biparental care is rarer and limited to some beetles, earwigs, termites and some cockroaches. It is known in the beetle Necrophorus spp. (not Nicrophorus, a typographic mistake, by someone ignorant of Greek) and in many Scarabeidae, e.g. Cephalodesmius (Monteith and Storey, 1981). Here, there is utilization of plant material and progressive provisioning for the growing larvae. In the last case, the male is closely involved. There is some task distribution between the two sexes. An exceptional case of biparental cooperation has been studied by Rasa (1998), in the Kalahari desert, with the tenebrionid Parasti%opus armaticps. Males dig and extend breeding burrows, while the female forages on the ground surface at night for the larval food.

Some insects, for protection of their offspring, have taken to viviparity, that is eggs develop within the body of the mother, and young larvae are laid. The chrysomeline Chrysolina shows viviparity in the Arctic in order to shorten the developmental period in hostile conditions outside mother's body, and Platyphora, in the neotropics, as a protection against hy-menopterous egg parasitoids. It has been mentioned above that larvae of Platyphora show cycloalexy for their protection. Some cockroaches are also viviparous, and may show a complex situation in this context. Eggs of the cockroach Diploptera punctata are very small, and there are complex "milk glands" opening into the female genital tract. Secretion of these glands provides nourishment to the developing stages within mother's body.

According to E. O. Wilson (1971), four ecological pressures result in selection for parental care in insects: 1) stable environment, 2) stressful environment, 3) the need for unpredictable resources, such as carrion or dung; 4) high predation pressure. It is definite that chrysomelids, which protect their offspring by their presence, are under pressure of heavy predation (by ants and bugs) and strong parasitoid pressure.

Providing protection to the offspring is quite widespread among insects. Parental care in insects, as defined by Michelle Pelissier Scott (in Resh and Cardé, 2003), ranges from covering eggs with a protective coating to remaining to feed and protect young to forming eusocial societies with life-long association of parents and offspring. Parental care is most developed in Isoptera (termites), Hemiptera, Homoptera, Dermaptera, Thysanoptera, Embioptera, Coleoptera and Hymenoptera, also in some Orthoptera, Psocoptera, and Diplura (Choe, 1989). It is exceptional among Lepidoptera; it is so far known in a single butterfly genus, Hypolimnas, in Guam and in the Philippines. Care of eggs is also rare among Diptera and is restricted to some genera and families and to some mosquitoes. Only a dozen, among thousands of Dermaptera, exhibit parental care. Among Dermaptera and Gryllotalpa (Orthoptera) , females protect their eggs by holding them in their mouth-parts and licking them regularly, thus using anti-fungal properties of their saliva. Embioptera are also known to pick up their eggs in their mouth-parts and to coat them with wood, silk and chewed-up food. Hemiptera often resort to wing-fanning to repel the parasites or predators. Some females add their eggs to a cluster already being guarded by another female. The female of some reduviid hemipteran, like Ghilianella, even carries her nymphs on her back. Embioptera, in their silk tunnels, cover carefully their eggs with macerated bark to repel hymenopterous parasites.

Half a dozen of books and many articles have been written on the topic of parental care in insects, and several encyclopedia have tried to summarize this rather complex problem (Preston-Mafham, R. and K. 1993; Resh and Cardé, 2003; Capinera, 2004). Reference is given here to the excellent review of parental care among insects done by Hinton (1981) in his trilogy on insect eggs.

— Fig. 33.1. Omaspides (Paromaspides) sobrina — Fig. 33.2. The same as Fig. 33.1. Parental care

Boheman (Coleoptera: Cassidinae), female (photo Jolivet). protecting its pupae. Vi^osa, MG, Brazil (photo Jolivet).

— Fig. 33.3. Gonioctena rufipes DeGeer (Chrysomelinae), female, protecting its young larvae. Germany.

— Fig. 33.4. Omaspides pallidipennis Boheman (Cassidinae), female, covering its young, as a hen. The abdomen of the larvae are outside the mother's elytra. Brazil.

— Fig. 33.5. Acromis spinifex Linne (Cassidinae), with its (after Jolivet, 1988). Brazil.

sap wood c'

hardened : glandular secretion

— Fig. 33.7. Ootheca of Chiridopsispromiscua (Cassidinae) (from Kalaichelvan and Verma, 2000). India.

sap wood c'

burrow stained black with a fungal growth

— Fig. 33.6. Female of Eugenysa — Fig. 33.8. Burrows of an ambrosia beetle (based on a cascaroni (Cassidinae) guarding photograph in Batra and Batra, 1967). her progeny, a group of pupae (after Jolivet, 1997). Brazil.

v J ' first formed eggless lamellae

— Fig. 33.9. Eggs of a golden eye (Chrysopa sp.) held on flexible stalks.

- -i lamellae with egg chambers

— Fig. 33.10. Ootheca of Aspidomorpha miliaris (Cassidinae). The arrow indicates the end attached to the leaf surface (from Kalaichelvan and Verma, 2002).

References

Batra, S. W T. and Batra, L. R. 1967. The fungus gardens of insects. Scientific American, 217:112-120.

Becker, M. and Friero-Costa, F. A. 1988. Natality and mortality in the egg stage in Gratiana spadicea (Klug, 1829) (Coleoptera, Chrysomelidae, Cassidinae), a monophagous cassidine beetle of an early successional Solanaceae. Rev. Bras. Biol 48: 467-475.

Capinera, J. L. 2004. Encyclopedia of Entomology. 3 volumes. Kluwer Academic Publishers, Dordrecht, The Netherlands.

Choe, J. C. 1989. Maternal care in Labidomera suturella Chevrolat (Coleoptera: Chrysomelidae: Chrysomelinae) from Costa Rica. Psyche 96: 63-67.

Hinton, H. E. 1981. Biology of Insect Eggs. Vol. 1. Pergman Press, Oxford, U. K.: 473 pp.

Jolivet, P 1988. Les soins parentaux chez les Chrysomélides. L'Entomologiste, Paris 44 (2): 93-101.

Jolivet, P 1997. Biologie des Coléoptères Chrysomélides. Boubée Publications, Paris.

Kalaichelvan, T. and Verma, K. K. 2000. Fecal cover for eggs of Indian cassidines (Coleoptera, Chrysomelidae). Insect Environment 6 (1): 41-42.

Kalaichelvan, T. and Verma, K K 2002. Formation of ootheca in Aspidoomoorpha miliaris F. (Coleoptera, Chrysomelidae, Cassidinae). Insect Environment 8 (3): 110-112.

Kudo, S.-I. and Hasegawa, E. 2003. Diversified reproductive strategies in Gonioctena (Chrysomelinae) leaf-beetles. In: Jolivet, P, Santiago-Blay, J. A. and Schmitt, M. (eds.). New Developments in the Biology of Chrysomelidae. SPB Academic Publ. bv, The Hague, The Netherlands: 727-773.

Lin, C.-P, Danforth, B. N. and Wood, T. K. 2004. Molecular phylogenetics and evolution of maternal care in Membracine treehoppers. Syst. Biol. 55 (3): 400-421.

Monteith, G. B. and Storey, R. I. 1981. The biology of Cephalodesmius, a genus of dung beetles which synthesizes "dung" from plant material (Coleoptera: Scarabeidae: Scarabeinae). Mem. Qd. Mus. 20: 253-277.

Olmstead, K L. 1996. Cassidine defenses and natural enemies. In: Chrysomelidae Biology, vol. 2 (Editors P Jolivet and M.L. Cox). SPB. Academic Publishing, Amsterdam: 3-21.

Preston-Mafham, Rod and Ken. 1993. The Encyclopedia of Land Invertebrate Behaviour. The MIT Press, Cambridge, Mass., USA: 320 pp.

Rasa, O. A. E. 1998. Biparental investment and reproductive success in a subsocial desert beetle: the role of maternal effort. Behav. Ecol. Sociobiol. 43: 105-115.

Resh, V H. and Cardé, R. T. 2003. Encyclopedia of Insects. Academic Press-Elsevier. Amsterdam. New York: 1266 pp.

Wilson, E. O. 1971. Insect Societies. Bellknap Press, Cambridge, Ma., USA.

Windsor, D. M. and Choe, J. C. 1994. Origins of parental care in chrysomelid beetles. In: Jolivet, P, Cox, M.L. and Petitpierre, E. ( eds.). Novel Aspects of the Biology of Chrysomelidae: 111-117.

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