Italian Xylocopini Research Project
Via Velardi 10 - Rione Arenula - 84014 Nocera Inferiore (SA: Campania) Italy
February 9, 2005
The largest insect eggs are those of carpenter bees (Xylocopini). The eggs of many species remain to be measured, but X. auripennis produced the largest egg reported thus far: 16.5mm in length and 3.0mm in diameter.
Chapter 7 of the University of Florida Book of Insect Records reviews the smallest eggs of insects. In order to complete this topic, the present paper is a bibliographical review of the largest insect eggs.
The following bibliographical databases were consulted for reports of measurements of the eggs of Xylocopini (carpenter bees): Biological Abstracts (from 1927), Zoological Record (from 1900), Apicultural Abstracts (from 1966), Entomology Abstracts (from 1969), Review of Applied Entomology Series A (from 1913). For data on egg size in other insects, Hinton's (1981) three-volume Biology of Insect Eggs and references therein were consulted.
After surveying the "egg capacity" of insects and the number and size of eggs in Hymenoptera, Iwata (1964) concluded that giant eggs were found only in the subsocial Hymenoptera and that the Xylocopini (carpenter bees) produced the largest insect eggs in absolute terms. However, Iwata gave no measurements for eggs other than for those of Hymenoptera, leaving uncertain how thoroughly he had reviewed egg size in other orders. Anderson (1972a, 1972b) lists representative egg dimensions for 21 species in 12 orders of hemimetabolous insects and 35 species in 8 orders of holometabolous insects. The longest eggs he lists for Hemimetabola are 6-8mm, for Locusta migratoria (Orthoptera); the largest eggs he lists for Holometabola are 3.75mm long × 0.85mm wide, for Chalicodoma muraria (Hymenoptera). Because Anderson did not report any measurements of carpenter bee eggs, it is evident that he may have missed the largest eggs in other orders as well. However, unable to find any evidence to the contrary, I assumed that Iwata (1964) was correct and confined my further efforts to researching the sizes of the eggs of Xylocopini.
Table 1 lists all the Xylocopini species with published data on egg size. The eggs of Xylocopa auripennis are largest, because they have the greatest diameter (3.0mm) and a length (16.5mm) that is equaled only by X. latipes. However, Iwata (1964) derived the egg dimensions for X. latipes (16.5 x 2.6) from measurements of a "near-mature ovarian egg" and suggested that future field observations may prove that X. latipes deposits the largest eggs.
Data on egg size are scarce. In order to complete the search for the largest egg, it will be necessary to measure adequate samples of the eggs of the largest Xylocopini species: Xylocopa fimbriata, X. flavorufa, X. frontalis, X. latipes, X. nigrita, X. tenuiscapa, X. torrida, X. tranquebarica (X. flavorufa and X. nigrita are included because they are polytypic species, making it desirable to supplement the existing data).
This chapter seeks to identify the insect eggs that are largest in absolute size, but it is worth noting that Iwata and Sakagami (1966) also attempted to determine which carpenter bees produced the largest eggs relative to the size of the female. To do that they calculated an egg index by dividing the length of the largest mature oocyte (EL) by the maximum distance between the outer rims of the female's tegulae (TD): egg index = EL/TD. As can be seen in Table 1, Xylocopa tranquebarorum has the largest egg index (2.00). However, the insect that produces the largest eggs relative to female size is probably not a carpenter bee. Sexual females of some aphids produce a single large egg that overwinters and the following spring produces a stem mother, whose success partly depends on her size - for example, Phylloxera vastatrix and Pemphigus betae (Iwata 1964, Whitham 1979).
Published measurements of eggs of Xylocopini.
|X. appendiculata||12.5||2.5||1.38||Iwata 1964, Iwata & Sakagami 1966|
|X. auripennis||16.5||3.0||1.72||Iwata 1964, Iwata & Sakagami 1966|
|X. bombylans||9.0||Houston 1992|
|X. flavorufa||13.0||2.5||Anzenberger 1977, Eardley 1983|
|X. imitator||10.0||2.3||Anzenberger 1977, Eardley 1983|
|X. iris||8.0||Bonelli 1967, Pagliano & Nobile 1993|
|X. latipes||16.5||2.6||1.38||Iwata 1964, Iwata & Sakagami 1966|
|X. nigrita||15.0||2.7||Anzenberger 1977, Eardley 1983|
|X. olivieri||7.2||1.7||1.09||Rozen & Özbek 2003|
|X. sulcatipes||11.0||2.2||Gerling et al. 1983, Maa 1970, Stark et al. 1990|
|X. tranquebarorum||13.0||Maeta et al. 1985|
|X. tranquebarorum||15.7||2.9||2.00||Iwata 1964, Iwata & Sakagami 1966|
|X. violacea||12.0||Janvier 1977|
|X. violacea||11.3||2.4||1.31||Vicidomini 1996|
Thomas J. Walker contributed to the research for this chapter.
- Anderson, D.T. 1972a. The development of hemimetabolous insects, pp. 95-163. In S.J. Counce and C.H. Waddington [eds.], Developmental systems: insects. v.1. Academic, London.
- Anderson, D.T. 1972b. The development of holometabolous insects, pp. 165-242. In S.J. Counce and C.H. Waddington [eds.], Developmental systems: insects. v.1. Academic, London.
- Anzenberger, G. 1977. Ethological study of african carpenter bees of the genus Xylocopa (Hymenoptera, Antophoridae). Z. Tierpsychol., 44: 337-374.
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- Iwata, K. 1964. Egg gigantism in subsocial Hymenoptera, with ethological discussion on tropical bamboo carpenter bees. Nature & Life S. E. Asia, Kyoto, 3: 399-434.
- Iwata, K., Sakagami, S.F. 1966. Gigantism and dwarfism in bee eggs in relation to the mode of life, with notes on the number of ovarioles. Jap. J. Ecol., 16(1): 4-16.
- Janvier, H. 1977. Comportamiento de Xylocopa violacea Linneo, 1758 (Hymenoptera). Graellsia, 32: 193-213.
- Maa, T.C. 1970. A revision of the Subgenus Ctenoxylocopa (Hymenoptera: Anthophoridae). Pacific Insect, 12(4): 723-752.
- Maeta, Y., Sakagami, S.F., Shiokawa M. 1985. Observation on nest aggregation of the taiwanese bamboo carpenter bee Xylocopa (Biluna) tranquebarorum tranquebarorum. (Hymenoptera: Anthophoridae). J. Kansas Entomol. Soc., 58(1): 36-41.
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- Rozen, J.G., Özbek, H., 2003. Oocyte, eggs and ovarioles of some long-tongued bees (Hymenoptera: Apoidea). Amer. Mus. Novit., 3393: 1-35.
- Stark, R.E., Hefetz, A., Gerling, D., Velthuis, H.H.W. 1990. Reproductive competition involving oophagy in the socially nesting bee Xylocopa sulcatipes. Naturwissenschaften, 77: 38-40.
- Vicidomini, S. 1996. Biologia di Xylocopa (Xylocopa) violacea (Linnè, 1758) (Hymenoptera: Apidae): l'uovo. Atti Soc. Ital. Sci. Nat. Milano, 137(1): 37-46.
- Whitham, T.G. 1979. Territorial behaviour of Pemphigus gall aphids. Nature 279: 324-325.