Does insect diversity differ between sites that are affected by myrtle rust?

Emma Carter
Vacation Research Experience Scholarship 2014

As threats and disruptors of native dynamics, invasive species are considered to be one of the central causes for the decline of biodiversity (Gurevitch & Padilla, 2004). Increasingly concerning, are pathogenic invaders that are of modest impact in communities where they have co-evolved, but are highly effective in regions they infect (Loope & Uchida, 2012).

Since its apparent introduction and initial spread in Australia (along the central NSW coast) during 2010, the highly invasive and pathogenic plant fungus, myrtle rust (Puccinia psidii) has posed significant threats to myrtaceous species in native ecosystems (Booth & Jovanovic, 2012; Carnegie & Cooper, 2011). The disease, particularly severe in seedlings and juvenile life stages, inhibits growth, induces defoliation and shoot mortality (Coutinho et al., 1998). Given the mega-diverse group of plant species that are susceptible its infection, myrtle rust is arguably a very significant issue in Australia, exacerbated by the uncertainties perhaps already facing threatened host taxa (Glen et al., 2007).

In the forest environment, the species diversity and structural complexity creates numerous niches (Franklin, 1970). The exploitation of such by different biota, particularly insects, is a central element in the dynamics of the system. Comprising key intermediate levels in the trophic system, insects are important decomposers and form the diet of higher order vertebrates. Others are key vectors in the pollination and subsequent reproduction of plants (Losey & Vaughan, 2006).

Myrtle rust has been observed to alter floristic structure and appearance (see Carnegie & Cooper, 2011). For insects that rely on the plant, this raises questions about how such changes might affect their behaviour, interactions and indeed prevalence with infected host plants. Do the bright yellow spores attract more insects, or do they deter them? Does the presence of myrtle rust influence the occurrence of these invertebrates?

Given the immense importance of insects, these questions seem reasonable to pose in part of understanding the wider implications of myrtle rust infection. This study therefore aims to ascertain if myrtle rust has any indirect or secondary effects on insect communities in severely and marginally affected sites.