DNA Diagnostics of Three Armored Scale Species on Kiwifruit in New Zealand

Abstract

Three species of armored scale (Hemiptera: Diaspididae) are found on kiwifruit (Actinidia spp.) in New Zealand orchards: latania scale, Hemiberlesia lataniae (Signoret); greedy scale, Hemiberlesia rapax (Comstock); and oleander scale, Aspidiotus nerii (Bouché). Each of them is a quarantine pest in some of the markets to which New Zealand kiwifruit are exported. Adult females of the three species can be distinguished morphologically; however, the task is laborious when large numbers must be identified. Furthermore, it is not possible to distinguish among the immature stages. A DNA-based diagnostic using a multiplex polymerase chain reaction (PCR) method based on differences in the cytochrome oxidase I and II genes was developed to distinguish the three species. The test relies on the rapid isolation of amplifiable DNA by using a protease (prepGEM), followed by multiplex PCR using primers that distinguish the species at three or more nucleotide positions within cytochrome oxidase I and II, resulting in PCR products of characteristic size for each species. The test was validated in a double-blind experiment and then used to determine the relative distribution and abundance of the three species on leaves and fruit of 'Hayward' and 'Hortl6A' kiwifruit across the dominant growing regions throughout New Zealand during the 2007 season. In total, 3,418 scale insects were identified to species level: 1,904 (56%) were latania scale; 1,473 (43%) were greedy scale; and 41 (1%) were oleander scale. Since the last survey in 1988, latania scale has displaced greedy scale as the dominant species of armored scale on Hayward kiwifruit in the North Island and was found for the first time in the South Island. Only a single latania scale was found on Hortl6A fruit, consistent with previous reports of reduced rates of settlement on the fruit of this cultivar by latania scale compared with greedy scale.

Measuring resistance to armoured scale insects in kiwifruit (Actinidia) germplasm

“…The differences in H. lataniae and H. rapax cap size in the commercial kiwifruit genotypes 'Hayward' and 'Hort16A' correlates well with the findings of a recent survey of armoured scale species on leaves and fruit of both genotypes of commercial kiwifruit at harvest throughout New Zealand in 2007 (Edwards et al 2008). On 'Hayward', H. lataniae comprised 72% of identifications on leaves and 69% on fruit; while on 'Hort16A', H. rapax comprised 70% of identifications on leaves and 99.5% on fruit.…”

“…Only adults of these two scale insect species can be determined to species using morphological characters, although a DNA probe has been developed since this work was done (Edwards et al 2008). The mean number of fruit per vine was 76 (range 33Á111).…”

“…The insect completes two moults before becoming an adult and may live for up to nine months ). Both scale insect species are resident on the wood of kiwifruit vines throughout the year, but also settle on leaves and fruit during the summer (Edwards et al 2008). H. rapax was first recorded in New Zealand in 1879 (Charles & Henderson 2002) and has been the main armoured scale pest of kiwifruit since its commercialization until very recently (Steven 1990;Edwards et al 2008).…”

“…Both scale insect species are resident on the wood of kiwifruit vines throughout the year, but also settle on leaves and fruit during the summer (Edwards et al 2008). H. rapax was first recorded in New Zealand in 1879 (Charles & Henderson 2002) and has been the main armoured scale pest of kiwifruit since its commercialization until very recently (Steven 1990;Edwards et al 2008). H. lataniae was found in New Zealand in 1979 (Morales 1988) and has slowly spread throughout the North Island over the past 25 years, displacing H. rapax as the dominant armoured scale pest on 'Hayward' but not 'Hort16A' kiwifruit (Berry et al 1989;Blank et al 2000;Edwards et al 2008).…”

The response of resistant kiwifruit (Actinidia chinensis) to armoured scale insect (Diaspididae) feeding

“…These insect species are both highly polyphagous and occur throughout the world in tropical to temperate zones (Miller and Davidson 2005;Normark and Johnson 2010;CABI 2009). Both species exist in New Zealand as uniparental, parthenogenetic populations, having two generations per year and are resident on the wood of kiwifruit vines throughout the year, settling on leaves and fruit during the summer (Edwards et al 2008).…”