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University of Queensland (2020)

Feeding ecology of green mirids : polyphagy and spatio-temporal dynamics across arid and agricultural environments

Cappadonna, Justin

Titre : Feeding ecology of green mirids : polyphagy and spatio-temporal dynamics across arid and agricultural environments

Auteur : Cappadonna, Justin

Université de soutenance : University of Queensland

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
Green mirids, Creontiades dilutus (Hemiptera, Miridae), are polyphagous bugs and are endemic to Australia. These bugs feed on a variety of plant species that grow across massive expanses of subcoastal agricultural landscapes in eastern Australia, as well as in the arid continental interior. Molecular evidence, along with field surveys, have demonstrated that C. dilutus bugs move long distances between native vegetation in the arid interior and crops in the eastern states of Queensland and New South Wales. These bugs arrive in the subcoastal agricultural landscapes every summer, and are important pests of cotton (Gossypium hirsutum L.) (Malvaceae). They feed on the soft tissues of cotton plants, including the developing flowers, which results in a substantial loss of fruit (cotton bolls) and the feeding damage delays harvest through the crops taking time to compensate for these losses.

The seasonal invasions of bugs into cotton are influenced by the high mobility of these insects and their ability to use a wide variety of host plant species across arid and agricultural landscapes. Some plant species are relatively good hosts in supporting the production of high numbers of nymphs, whereas others produce few nymphs but may be used incidentally as shelter, and this may aid in the dispersal of the adults across long distances. The timing of invasions of C. dilutus bugs into cotton, and the pathways followed by them are poorly understood. Also, the general mechanisms by which these insects localize appropriate host plants have not been subject to much investigation.

Host plant availability in the arid continental interior is dependent on highly variable localized rainfall, and such areas are separated by large expanses of extremely dry regions containing few green plants. In agricultural systems, non-crop plants along roadsides and the margins of farms occasionally host low densities of bugs, but previous field surveys have not found high densities of C. dilutus that may act as a source of pests that invade cotton. Within farms several legume crops, such as lucerne (Medicago sativa) and pigeon pea (Cajanus cajan) (Malvaceae), routinely support high bug densities, whereas nearby cotton crops host substantially fewer bugs. Gut analyses conducted previously suggest that individual mirids do move from lucerne into cotton, but they also move in the other direction, despite the differential numbers of bugs across these crops. Similar movement patterns across pigeon pea and cotton “boundaries” were evaluated in this thesis.

The ambiguity in the dispersal and host use patterns of C. dilutus bugs makes it difficult for pest managers to predict invasions of these insects into cotton, with accuracy. Consequently, researchers are not able to design effective management strategies. With a better understanding of dispersal and host use patterns of C. dilutus bugs, it may be possible to reduce the number of insecticide sprays in cotton if bugs could be attracted away from cotton by planting alternative hosts (trap crops), but these alternative hosts may inadvertently become local reservoirs of pests that move into cotton. A particular aim of this study is, therefore, to investigate aspects of the dispersal of these C. dilutus bugs across crop host species and the associated host localization behaviour of these insects. The ultimate goal is to use this information to form a conceptual model for the host localization process of C. dilutus bugs and provide a realistic framework to develop effective pest management decisions in cotton systems.

Mots clés : arrestment cotton Creontiades dilutus green mirid insect dispersal multiple host-use refuge crop


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