THE INCIDENCE OF PARASITISM AND DISEASE IN FIELD POPULATIONS OF THE POTATO MOTH PHTHORIMAEA OPERCULELLA (ZELLER) IN AUSTRALIA

Abstract

The incidence of parasitism and disease was recorded during a survey of Phthorimaea operculella populations from the major Australian potato growing areas. High levels of parasitism were found in most regions, though the contribution of each of the three major species showed marked geographic variation. There were also differences in the parasitism of larvae in leaves and in tubers. In some locations larvae were infected by a granulosis virus, which appeared to be endemic at a low frequency throughout the potato moth's range in Australia.

Geographic variability in demographic performance of the potato moth, Phthorimaea operculella(Zeller) (Lepidoptera: Gelechiidae), in Australia

“…In 1946 and 1964-66, three exotic parasitoids were introduced into Australia and became successfully established (Callan, 1974). These species, Copidosoma desantisi Annecke & Mynhardt, Apanteles subandinus Blanchard and Orgilus lepidus Muesebeck, are now present throughout the range of P. operculella in various combinations and cause up to 80-90% mortality in local populations (Franzmann, 1980;Briese, 1981). There is, however, a marked difference in the seasonal pattern of parasitization between the warm northern areas (typified by the sites of Tolga, Grantham and Lawrence) and the cooler southern regions in which P. operculella is found.…”

“…Field-collected larvae were placed on potato tubers at a density of 1 larva/2 gm potato and allowed to complete their development in the laboratory. Unfortunately, because of the high levels of parasitism at many sites (Briese, 1981), the numbers of adults produced from field-collected larvae were relatively small in some cases (Table I).…”

The Potato Tuberworm: A Literature Review of Its Biology, Ecology, and Control

“…Other parasitoids like Tachinidae (Incamyia cuzcensis T.T. and Lixophaga diatraeae Towns), and more than 60 Hymenoptera (Braconidae, Encyrtidae, Eulophidae, Ichneumonidae, Mymaridae, Perilampidae, Pteromalidae, Scelionidae, and Trichogrammatidae) have also been described by several authors (Labeyrie 1959;Lloyd and Guido 1963;Jai Rao 1967;Rao 1967;Rao and Ramachandran-Nair 1967;Leong and Oatman 1968;Rao and Nagaraja 1968;Oatman et al 1969;Lloyd 1972;Odebiyi and Oatman 1972;Cruickshank and Ahmed 1973;Callan 1974;Oatman et al 1974;Oatman and Platner 1974;Cardona and Oatman 1975;Chundurwar 1977Chundurwar , 1978Odebiyi and Oatman 1977;Mitchell 1978;Divakar and Pawar 1979;Franzman 1980;Sankaran and Girling 1980;Briese 1981;Oatman 1982, 1987;Powers and Oatman 1984;Izhevskiy 1985;Horne 1990Horne , 1993. Among all parasitoids listed, there are some ecological differences; for instance, while C. desantisi oviposits in the eggs, A. subandinus and O. lepidus prefer young P. operculella larvae (Platner and Oatman 1972a).…”

“…However, in some instances, parasitism and predation has been estimated at 40% and 79%, respectively (Coll et al 2000). Level of parasitism was found higher in larvae feeding in the leaves (65%) as compared to larvae infesting tubers (32%) (Briese 1981), suggesting that parasitoids find it easier to encounter the host in exposed potato leaves rather than on tubers buried in the ground. Callan (1974) unsuccessfully tried to correlate parasitism and field damage; he indicated that since parasitism does not lead to instant mortality, it cannot provide immediate control, therefore raising some questions regarding the efficacy of the use of natural enemies.…”

“…Another explanation for this discrepancy may be the difference in susceptibility or the potential development of resistance to a GV strain between fields populations occurred in P. operculella Australia population. Timing of virus applications (Briese 1981;Briese and Mende 1981). Timing of virus applications (Reed 1971;Reed and Springett 1971), methods of application, concentration, and ultraviolet radiation can influence effectiveness of control (Kroschel et al 1996a, b;Sporleder et al 2001Sporleder et al , 2005Sporleder 2003).…”