33 A SUMMARY OF CERTAIN ASPECTS OF THE SCARAB PROBLEM, AND A CONTRIBUTION TO A BIBLIOGRAPHY OP THE FAMILY SCARABAEIDAE. By D. Margaret Cumpston, M.Sc* [Read 26th March, 1941.] Dui'ing the last two years the writer has carried out certain investigations on the larvae of Australian species of the family Scarabaeidae. It is thought that a summary of certain aspects of the problem, together with a bibliography of the literature consulted during the work, may be of future use. In an appendix two bibliographical lists have been included; the first deals with work done overseas, and is subdivided into morpho-logical, physiological, ecological and miscellaneous sections, together with some papers on breeding and rearing technique; the second, dealing with Australian economic species, is listed under the host plants. The first list includes only relatively few publications out of the mass of literature dealing with this group, and is published in the hope that it may save part, at least, of the preliminary reading necessary in starting any pi-oblem. The second list is not entirely complete, but does cover most of the species known to be injurious. A Summary of Certain Aspects of Conditions Affecting Scarabaeidae of Economic Importance. The eggs are laid some inches below the soil surface, in spring and early summer, being usually deposited in clusters in cavities made by the female. The larvae work their way upwards after hatching, and feed at varying depths below the soil surface. Feeding generally takes place at night: the larvae may approach the surface sufficiently close to disturb it. There are three instars: the total life-cycle ranges from three or four months to three years (in some North American Scarabaeidae). Feeding takes place all through the summer. During the winter the larvae are found at greater depths, enclosed in small cells moulded by pressui'eof the body on the surrounding soil particles. This cell may also be formed at any time when the larva is not feeding. The depth to which the larvae descend depends on the climate, the size of the larva and the ease of penetration. The following spring, the larvae work their way up again and feed on the young roots. In young plants the roots are cut off right to the stem, all new rootlets devoured, and the plant may even be pulled entirely under the surface as the larva feeds. It is at this time that the damage is most apparent, becoming manifest as areas of stunted growth and dead plants. Plants are always more affected where conditions are adverse to vigorous growth, but these conditions usually also render the soil habitat more unfavourable for larval development. Where growth is strong, the plants may outgrow the grub attack; this is an important factor in limiting larval damage. In those species with a two-year life-cycle the damage is greater and extends over a more prolonged period, the larvae passing two winters in a dormant state. The damage even with the heaviest grub population is not very apparent until the final instar. When the larva is fully grown it again burrows downwards. Ritcher (1939) states that the depth of pupation varies with the species and the type of soil; he concludes that soil factors may affect the pupation levels, but do not alter the relative positions of the various species, and also that differences in latitude seem to have little effect on the depth at which a given species pupates. The larva enters the prepupal state when it sheds the rectal contents, which are used as a plaster in the formation of the ovoid pupal cell. This plaster ensures a fairly firm and impermeable structure. The prepupa has a creamy-white appearance, and just prior to pupation is incapable of any move-ment but a restricted jerking of the abdomen. The pupa is of the exarate type. The adult requires several days after emergence before it hardens and assumes the proper colouration: until then it does not leave the pupal cell. The adults usually first emerge * This paper was prepared when the writer held a Linnean Macleay Fellowship in Zoology. f
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