Excised Leaf Bioassay: Phenotypic Expression of Natural Resistance in Apple against the Obliquebanded Leafroller

Abstract

Different approaches were assessed in the development of a bioassay method that would provide data necessary to evaluate resistance of apple genotypes to the obliquebanded leafroller (OBLR) Choristoneura rosaceana (Harris). A leaf disc method used to evaluate the impact of pesticides on leafrollers resulted in high levels of leaf-abandonment of first and second instar larvae. Inserting leaf petioles into water soaked Oasis foam resulted in a significant reduction in overall leaf weight and diminished the appearance of leaf quality. When leaf petioles were inserted into waterfilled Eppendorf vials, leaf weight increased and overall leaf quality appeared to be good. We opted to adopt this latter whole-leaf bioassay method, which though very time consuming, provided a robust assessment of OBLR life history parameters against different apple genotypes. Across all apple genotypes evaluated, male larvae developed faster than females to pupation as well as to adulthood, while females developed faster as pupae and were heavier than male pupae. OBLR larvae reared on leaves from different apple genotypes displayed significant variability in development time, pupal weight, larval survivorship, and number of offspring produced. We utilized three indices to characterize host acceptance, sub-lethal effects, and lethal effects of OBLR to apple genotypes. Our results indicated that 'Lady', 'Viking', and 'Northern Spy' show some of the highest levels of resistance against OBLR, while 'Granny Smith' was quite susceptible to OBLR and could be used in future studies identifying apple genotypes with relative resistance to OBLR.

Pneumatic spray delivery‐based solid set canopy delivery system for oblique banded leaf roller and codling moth control in a high‐density modern apple orchard

“…CM larvae feed on the fruit internally and make it unmarketable 7 . Similarly, OBLR feeds on the foliage and fruits close to foliage causing significant fruit damage 6,8 …”

“…7 Similarly, OBLR feeds on the foliage and fruits close to foliage causing significant fruit damage. 6,8 Airblast sprayers are the most common technology used for applying crop protectants to apples in the United States and WA state. 9,10 Although these sprayers were initially designed for traditional tall, spherical canopies, most apple orchards have transitioned to high-density, linear canopy architectures (for example, tall spindle, v-trellis and bi-axis).…”

“…These complexes, if not managed properly, can adversely affect the crop yield and result in suboptimal fruit quality. Codling moth (CM, Cydia pomonella ) and obliquebanded leafroller (OBLR, Choristoneura rosaceana (Harris)) are the most damaging insects infesting apples in WA state 5,6 . CM larvae feed on the fruit internally and make it unmarketable 7 .…”

“…Codling moth (CM, Cydia pomonella ) and obliquebanded leafroller (OBLR, Choristoneura rosaceana (Harris)) are the most damaging insects infesting apples in WA state. 5 , 6 CM larvae feed on the fruit internally and make it unmarketable. 7 Similarly, OBLR feeds on the foliage and fruits close to foliage causing significant fruit damage.…”

“…7 Similarly, OBLR feeds on the foliage and fruits close to foliage causing significant fruit damage. 6 , 8…”