The biology of Mycopsylla fici Tryon on its sole host, Ficus macrophylla Desf. ex Pers

Mycopsylla fici Tryon, the Moreton Bay fig psylloid, is a small hemipteran in the family Homotomidae, in the suborder Psylloidea. Its sole host is Ficus macrophylla Desf. ex Pers.,known as the Moreton Bay fig. Both species are endemic to eastern Australia. M fici has become notorious for apparently being the causative agent for the complete periodic defoliation of its host. The general aims of this thesis were: to investigate and provide good understanding of the biology of M. fici; and to determine, if possible, whether the insect is indeed primarily responsible for the defoliation of its host. The thesis includes an introduction to the psylloid, its host, and some general ideas about plant-insect interactions (in order to place the psylloid and the fig in the broader context of the literature on this topic); a geographical survey of the psylloid and its host within the host’s known range; a description of attempts to breed the psylloid under laboratory conditions; a description of the distribution of the psylloid in the host’s canopy with specific reference to the necessity for studying the psylloid in situ (i.e.,directly on its host); a survey of the fauna within the F. macrophylla canopy; detailed in situ studies of the phenology and population dynamics of the psylloid, including observations of its single known parasitoid, the encyrtid wasp Psyllaephagus sp.; and studies of F. macrophylla health inferred from a number of Fast Chlorophyll Fluorescence Kinetics {FCFK) analyses of the photosynthetic systems in host leaves. Various urban, semi-rural and rainforest sites were visited along the eastern seaboard and hinterland of Australia, and in Adelaide, where F. macrophylla grows either as a cultivated specimen, or naturally. Although there were fewer “naturally-occurring” F. macrophylla specimens observed than in urban and semi-rural conditions, the psylloid only seemed apparent when the host was growing in the latter types of environment. The psylloid was found to avoid ovipositing on F. macrophylla plants younger than approximately three years of age, or under 1.5 m in height, and to be selective as to choice of leaf age (irrespective of plant age) when laying eggs. Oviposition was observed to occur, usually, on the third to fifth leaves back from the first fully unfurled leaf on a branchlet. Attempts to breed psylloids on saplings in sufficient quantities for detailed life history studies in the laboratory proved to be impractical, which meant that all studies of the psylloid were made in the field. Results of an experiment to determine the distribution of M fici in the host canopy indicated that the psylloid showed no distinct preference for the particular regions of the tree with respect to height, and therefore that sampling studies could be made from the ground. A study to determine arthropod fauna/functional groups, and the relationship that they might have with the psylloid, and the host, identified no parasitoids of the psylloid other than the already-known Psyllaephagus sp. wasp. An undescribed species of thrips was discovered on F. macrophylla, and this insect may be an intra-niche competitor of the psylloid. Results from the life history studies indicated that a psylloid had an approximately 3.75% chance of surviving from oviposition to adulthood. Major causes of mortality for the pre-adult stages of the psylloid were identified as leaf fall from the tree, egg predation by coleopterans (by inference), predation of psylloid juveniles (mobile hatchlings and older lerp dwellers) by lacewing larvae, and parasitism by Psyllaephagus sp. Psyllaephagus sp. appears to be the single most effective biological control agent. A second, smaller, form of the Psyllaephagus sp.female was discovered, as was the occurrence of multiple parasitisation of individual psylloids. This latter observation suggests that Psyllaephagus sp. may be polyembryonic (a common trait amongst encyrtids), and that this in turn might influence its effectiveness as a biological control agent. Degree-day models for the psylloid were developed, and are discussed in relation to various urban sites included in the geographical survey. Fast Chlorophyll Fluorescence Kinetics (FCFK) analysis of Photosystem II (PSII) within sample leaf laminae of five F. macrophylla specimens growing in the Royal Botanic Gardens and Domain in Sydney indicated that photoinhibition in F. macrophylla leaves was more pronounced in periods of high psylloid density than in periods of low psylloid density. Other significant factors in F. macrophylla photoinhibition were attributable to the variability between individual trees (in both low and high psylloid “plague” density periods). Sunlight appeared to be the major influence on photoinhibition during periods of low psylloid density.Trees showing the best overall health and the least tendency to be affected by the psylloid were those growing in good soil conditions and (especially) those that had access to adequate water. These observations were supported by a comparison FCFK study and observations of growing conditions of five F. macrophylla specimens in and adjacent to the Adelaide Botanic Gardens,the psylloid not being present in Adelaide. It was ultimately concluded that the psylloid was producing a detectable effect on the health of the trees, but was not the sole, or even main, actor involved. It seems most likely that the amoimt of available water and, to a lesser degree, nutrients are also major, if not limiting,factors influencing F. macrophylla health and defoliation events. The increase in resources allocated to maintaining F. macrophylla specimens growing in public recreational areas is strongly recommended.