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

Abstract

A laboratory bioassay is described for measuring the resistance of kiwifruit vines to armoured scale insects (Hemiberlesia lataniae Signoret and Hemiberlesia rapax Comstock) using excised canes. The method measures the area of the scale cap using a template and compares relative cap sizes between genotypes. The method was tested for two species of kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang et A.R. Ferguson and Actinidia chinensis Planch.) using a range of experimental genotypes and two commercial varieties. Large differences in the susceptibility of the genotypes to H. lataniae were observed, but much smaller differences were observed for H. rapax. The bioassay method was tested by comparing results obtained with observations of armoured scale insects on kiwifruit vines in the field. Sampling of simulated scale populations showed that differences in population mean scale cap areas of 0.3Á0.5 mm 2 could be detected with sample sizes of 50Á200. A bioassay of H. lataniae growth on an experimental genotype, comparing it with the commercial kiwifruit cultivars 'Hayward' and 'Hort16A' and using a template to categorize scale cap size into 0.2 mm 2 size categories, showed that the technique was quick, reliable and able to discriminate between kiwifruit varieties. This method could be easily adapted to test the susceptibility of germplasm from a variety of different horticultural plants to a wide range of armoured scale insect pests.

Defence Responses Associated with Elicitor-Induced, Cultivar-Associated Resistance to Latania Scale in Kiwifruit

“…The mobile dispersal stage (crawler) that emerges from the egg beneath the adult’s scale cap survives for up to one day before settling permanently on the host, spinning a protective cap over itself (which is firmly attached to the plant host), and remains sessile for the remainder of its life cycle. The cap grows as the insect body underneath increases in size, with the insect going through two moults before achieving maturity, approximately 10 weeks after settlement on kiwifruit [ 5 ]. Latania scale is highly polyphagous, and its ability to survive on more than 78 families of host plants, together with its worldwide distribution, make it an invasive pest of global significance [ 6 ].…”

“…deliciosa ‘Hayward’ and yellow-fleshed Actinidia chinensis var. chinensis ‘Hort16A’ [ 5 ]. Pest and disease resistance were not used as selection criteria for developing new cultivars, such as ‘Hort16A’ in the early 1990s, but subsequently, it was found that ‘Hort16A’ was very tolerant to the latania scale, whilst ‘Hayward’ was susceptible [ 5 ].…”

Transcriptome Analysis of Kiwifruit (Actinidia chinensis) Bark in Response to Armoured Scale Insect (Hemiberlesia lataniae) Feeding

“…lataniae crawlers were brushed onto the canes from a laboratory culture grown on squash and allowed to settle under wool yarn wrapped around the cane about 8 times. Details of this method which was developed for germplasm screening for resistance, are published elsewhere [ 5 ]. Photographs of the developing scale insects were taken at 1–2 week intervals from 9 January, when the insects were 2 months old, to 21 February 2014 and the areas of the scale insect covers were measured from the photographs using ImageJ (v1.47v) using a method published elsewhere[ 30 ].…”

Diaspidid (Hemiptera: Coccoidea) size plasticity as an adaptive life history trait

“…On 19 September 2007 the canes were removed from cold storage and forty-centimetre lengths were cut from 10 canes of each variety and prepared for bioassay (Hill et al, 2010). Buds were cut from the cane sections and grafting wax applied to all exposed tissue with the exception of the bottom end of the cane, which was placed into a plastic cup containing water.…”

“…Bark of the variety A. deliciosa "Hayward" is susceptible to H. lataniae, whereas the bark of A. chinensis "Hort16A" is completely resistant (Hill et al, 2007. A third variety, A. chinensis "Hort22D", showed partial resistance, supporting the growth of H. lataniae but resulting in adult insects that were estimated to be one-fifth of the size of mature H. lataniae grown on A. deliciosa "Hayward" (Hill et al, 2010). In spite of their small size, the H. lataniae adults grown on A. chinensis "Hort22D" were perfectly formed, produced mature embryos and laid eggs that hatched into healthy crawlers.…”