Seasonal Phenology and Climate Associated Feeding Activity of Introduced Marchalina hellenica in Southeast Australia

SIMPLE SUMMARY: Giant pine scale, Marchalina hellenica Gennadius (Hemiptera, Marchalinidae), is a sap sucking insect native to the Eastern Mediterranean Basin. In 2014, giant pine scale was detected for the first time in Victoria, Australia, feeding on a new host, Pinus radiata. We studied the life cycle and feeding activity of giant pine scale in Victoria over 32 months, with the aim of drawing comparisons between exotic and native populations. Australian life stages of this pest emerged during similar months to Greek seasonal equivalents, although the timing of Australian life stages differed between years. Insect density and feeding activity on infested trees differed among locations and between generations. Strong evidence was found in support of density and feeding intensity being explained by climatic conditions. The value of Pinus radiata as a food source for this insect may fluctuate with climate conditions. Our findings aim to inform future management efforts for this scale insect, including surveillance strategies and optimal seasons for release of biocontrol agents. Our findings also suggest that the impact of this pest in Australia may be exacerbated by climate change. ABSTRACT: Invasive insects pose an increasing risk to global agriculture, environmental stability, and public health. Giant pine scale (GPS), Marchalina hellenica Gennadius (Hemiptera: Marchalinidae), is a phloem feeding scale insect endemic to the Eastern Mediterranean Basin, where it primarily feeds on Pinus halepensis and other Pinaceae. In 2014, GPS was detected in the southeast of Melbourne, Victoria, Australia, infesting the novel host Pinus radiata. An eradication program was unsuccessful, and with this insect now established within the state, containment and management efforts are underway to stop its spread; however, there remains a need to understand the insect’s phenology and behaviour in Australia to better inform control efforts. We documented the annual life cycle and seasonal fluctuations in activity of GPS in Australia over a 32 month period at two contrasting field sites. Onset and duration of life stages were comparable to seasons in Mediterranean conspecifics, although the results imply the timing of GPS life stage progression is broadening or accelerating. GPS density was higher in Australia compared to Mediterranean reports, possibly due to the absence of key natural predators, such as the silver fly, Neoleucopis kartliana Tanasijtshuk (Diptera, Chamaemyiidae). Insect density and honeydew production in the Australian GPS population studied varied among locations and between generations. Although insect activity was well explained by climate, conditions recorded inside infested bark fissures often provided the weakest explanation of GPS activity. Our findings suggest that GPS activity is strongly influenced by climate, and this may in part be related to changes in host quality. An improved understanding of how our changing climate is influencing the phenology of phloem feeding insects such as GPS will help with predictions as to where these insects are likely to flourish and assist with management programs for pest species.