An ecological study of two dung beetles (Coleoptera, Scarabaeninae) with contrasting phenologies

Tyndale-Biscoe, Marina (1985) An ecological study of two dung beetles (Coleoptera, Scarabaeninae) with contrasting phenologies. PhD thesis, James Cook University of North Queensland.

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The literature on age-grading techniques of adult insects, published since 1968, is reviewed. This is followed by a study of the phenologies of two dung beetle species: the native Onthophagus granulatus Boheman, and the introduced Onitis alexia Klug, using age-grading techniques together with field and laboratory experiments.

At Uriarra, NSW, Ot. granulatus is a univoltine species which emerges in the summer or early autumn. It spends the remainder of the warm season in the maturation-feeding phase, a period which generally coincides with the presence of dung produced from a senescent and dried-off pasture. A proportion of beetles may begin breeding before the onset of cold weather, but the progeny do not survive the winter. The species over-winters underground in the adult stage, and reappears in the dung pads in the spring, when dung is generally produced from actively growing pastures. Oviposition occurs in the spring and early summer, and the adults die about the time of the emergence of the new generation. Periodic drought reduces the population by causing follicle resorption in the females and larval mortality. This was confirmed in laboratory experiments which showed that dung from hayed-off pasture caused high mortality in teneral adults, reduced fecundity in sexually mature females and caused high mortality in the pre-adult population. Additionally, dry conditions during larval development caused total mortality in the laboratory.

At Armidale, NSW, the species has basically the same life cycle except that a small proportion of larvae survive the winter and emerge as adults in the following spring.

Newly emerged Oi. alexia at Araluen begin to appear in pads in the late spring, and new emergence continues into the summer. The maturation-feeding phase is short, and oviposition starts within a week or two of emergence. Eggs laid in December/January develop to emerge as adults in late summer and autumn, eggs laid in February and later do not give rise adults until the following season. The species over-winters mainly in the larval stages, though a proportion of adults may survive the winter in some years. The species at Araluen is thus partly univoltine and partly bivoltine. The population was greatly reduced by cold, wet winters. Dung from hayed-off pasture caused some decrease in fecundity, though not as great as occurred in Ot. granulatus, and it also caused some mortality in the larvae. Follicle resorption occurred in response to rainfall.

Additionally, older Oi. alexis were more likely to resorb their follicles than were younger beetles, whereas all sexually mature Ot. granulatus were equally likely to resorb.

Temperature summation calculations showed that the predicted and observed times of emergence of Ot. granulatus arising from eggs laid in the field under experimental conditions coincided well, and they occurred at times of peaks of new emergence as determined by age-grading. Predicted times of emergence of the 1982-83 summer population of Oi. alexis always preceeded the observed emergence time, indicating the presence of a larval diapause.

Diapause in the third instar larvae of Oi. alexis was found to be facultative, and occurred in response to cold temperature and dry conditions during larval development, and to short daylength experienced by the parents. As well, progeny of young parents were more likely to enter diapause than were the progeny of older parents.

Ot. granulatus is dependent on summer rainfall, and is unable to survive and breed well in dung produced from hayed off pastures. Temperatures above 30°C are lethal to the species. Its distribution is therefore very limited. Oi. alexia, in contrast, can survive dry summers and cold, dry winters (down to about 0°C) by entering diapause, and can breed in dung produced from dry pastures, though the survival of larvae is reduced. Its distribution appears to be limited only by cold wet winters. It has therefore spread from hot summer rainfall areas through regions of even rainfall and into temperate winter rainfall climates.

Item ID: 33795
Item Type: Thesis (PhD)
Keywords: adult insects; age-grading; Armidale (NSW); dung beetles; growth; life-cycle; Onitis alexia; Onthophagus granulatus; Uriarra (NSW)
Date Deposited: 21 Jul 2015 05:32
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060803 Animal Developmental and Reproductive Biology @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960804 Farmland, Arable Cropland and Permanent Cropland Flora, Fauna and Biodiversity @ 100%
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