The Japanese beetle (Popillia japonica Newman) is an invasive beetle belonging to the family of Scarabaeidae. First discovered in Riverton, NJ, in 1916 (Fleming, 1976), it is one of the most widespread and destructive insect pests in the eastern United States. The direct cost of renovating or replacing turf damaged by larval root pruning and defoliation of ornamental plants by adults has been estimated to exceed $450 million each year (Potter and Held, 2002). Adult Japanese beetles attack mostly the foliage, flowers, and fruit of more than 300 plant species in 79 families (Fleming, 1972).
Japanese beetles have one generation per year in the areas in which blackberries are cultivated commercially. The larvae of this species overwinter in the soil, then pupate in the ground and emerge as adults in early summer (Tashiro, 1987). After emergence, adult beetles disperse and aggregate on plants in close proximity to the areas where they have overwintered, and they then mate. Gravid females lay eggs in the ground, starting a new generation. Both sexes damage the plants by skeletonizing leaves and feeding on flowers.
In the United States, production of cultivated blackberries exceeds 30,000 t yearly (Clark and Finn, 2011; Strik et al., 2007), making the United States the second largest producer of blackberries in the world. Blackberry production area increased by more than 30% between 1995 and 2005, and Strik et al. (2007) predicted a further increase of 30% by 2015. Clark and Finn (2011) have listed several reasons for this increase, emphasizing the introduction of new blackberry cultivars with improved shipping characteristics. They have also pointed out that disease and insect resistance should become the focus for further breeding efforts.
The Japanese beetle is a serious insect pest of blackberries (Clark and Finn, 2011). Control of this pest is possible using pesticides. However, identification of blackberry cultivars with natural resistance to Japanese beetles could help to minimize environmental pollution and worker exposure to chemicals. This area of research is heavily understudied. We were able to locate only one article that investigated this issue (Johnson et al., 2010). The authors of that report evaluated the damage from Japanese beetles on 18 blackberry cultivars in Fayetteville, AR, by visually rating the degree of canopy defoliation. They found that Apache was the most sensitive, and PrimeJan was the most resilient cultivar.
The objectives of our study are to compare seasonal changes in population densities of Japanese beetles, CDD to peak beetle emergence, differences in percentages of blackberry leaves in canopies infested with Japanese beetles (damage incidence), and ratings of severity of leaf damage among 13 blackberry cultivars.
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