Progress 10/01/04 to 09/30/07
Outputs
Potato tuberworm is a very destructive insect pest of cultivated potato and in the last few years has been become established in the Columbia Basin region of Oregon, Idaho and Washington State. Significant damage to cultivated potatoes has been reported regardless of scheduled insecticide applications suggesting the presence of significant levels of insecticide resistance in this population. We examined the dose response of the Columbia Basin (OR) field population to three current insecticides (esfenvalerate, fipronil, methamidophos) and used an inbred laboratory population (CO) as a susceptible control.
Impacts
An inbred population of potato tuberworm reared in a laboratory for < 30 years, was resistant to three currently marketed insecticides at field application rates, possibly indicating that this population (CO) had been exposed to at least 2 of the tested insecticides prior to being collected for laboratory mass rearing. A field population from the Columbia Basin (OR) was insensitive to esfenvalerate and fipronil although the latter material is not widely labeled for U. S. field crops except corn and has not yet been approved for use on potatoes. However, this population might have been directly or indirectly exposed to pesticides with the same class or mode of action resulting in cross-resistance to fipronil. This study provides base information about potato tuberworm insecticide resistance and suggests that recent field failure of insecticides in Columbia Basin potato production was due, in part, to insecticide resistant potato tuberworm.
Publications
- Dogramaci, M. & W. M. Tingey. 2007. Comparison of insecticide resistance in a North American field population and a laboratory colony of potato tuberworm (Lepidoptera: Gelechiidae). J. Pest Science. DOI: 10.1007/s10340-007-0178-5.
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Progress 01/01/06 to 12/31/06
Outputs
Larval survival and growth of potato tubermoth, Phthorimaea operculella Zeller, colonies from Colorado and Oregon (Columbia Basin field population) were studied by rearing on insect-susceptible (cv. Allegany) and insect-resistant (cv. Q174-2) potato cultivars. Intact tubers of Q174-2 significantly reduced larval performance of the Colorado colony. However larval establishment of the Columbia Basin field population on intact tubers of Q174-2 was similar to that of on intact tubers of Allegany. Larval survival of the Colorado colony was significantly increased when neonates were placed on sliced tubers of the both cultivars; however greater numbers of larvae survived on sliced tubers of Allegany. Larval survival of the Columbia Basin field population on intact and sliced tubers of Allegany and Q174-2 was similar. Larval weight of the Colorado colony on Q174-2 and Allegany was greater than larval weight of the Columbia Basin field population on Allegany and Q174-2
respectively. Larvae of both populations consumed 52-64 percent more tuber tissue of Q174-2 than that of Allegany to gain same amount of body weight.
Impacts
Although tubers of an insect-resistant potato clone, Q174-2, suppressed larval feeding and growth of a Colorado PTM population, a field population of PTM from the Columbia Basin was largely affected. This finding suggests that these two pest populations are genetically different with respect to host adaptation and reinforces the importance of determining the genetic basis of Q174-2 tuber resistance, a trait of potential value where non-resistant PTM populations exist. Although further tests are needed, our currently available data indicates that the resistance modality of Q174-2 may not be effective against virulent PTM populations such as that currently creating management problems in the Columbia Basin potato production regions of Oregon and Washington.
Publications
- Malakar, R.D. & W.M. Tingey. 2006. Aspects of tuber resistance in hybrid potatoes to potato tuber worm. Entomol. Exp. Appl. 120: 131-137.
- Medeiros, A.H. & W.M. Tingey. 2006. Glandular trichomes of Solanum berthaultii Hawkes and its hybrids with S. tuberosum L. affect nymph emergence, growth, development and survival of Empoasca fabae (Harris) (Homoptera: Cicadellidae). J. Econ. Entomol. 99: 1483-1489.
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Progress 01/01/05 to 12/31/05
Outputs
Survival of nymphs, males and females of the potato leafhopper, Empoasca fabae (Harris), on six potato genotypes with varied levels of resistance was evaluated and related to type, density and droplet/head size of foliar glandular trichomes. Survival was greater on Solanum tuberosum cultivars (Allegany and Elba) compared to accessions of the wild S. berthaultii (PI 473331 and PI 473334). The barrier provided by glandular trichomes may affect survival of E. fabae by restricting nymph and adult feeding. PI 473331 was the most pubescent host, bearing Type A and Type B trichomes and the most unsuitable host for E. fabae. Allegany possesses leaflets with low trichome densities and small gland diameter and was the most suitable host for adult E. fabae survival. Females generally had higher survival rates than males. Nymph and adult leafhoppers differed greatly in their survival rates, particularly on S. tuberosum x S. berthaultii hybrids (Q174-2 and NY123). Interestingly,
nymphs had longer (190 days) mean lethal time (LT50) than adults (31 days) when held on Q174-2, and a lower LT50 (19 days) when held on NY123 compared to adults (104 days). Starvation and/or dehydration was likely associated with mortality of nymphs confined on PI 473331 and PI 473334. Nymphs on these accessions died at a comparable rate to those confined on a starvation treatment and more rapidly than those supplied with water only, sucrose solution or other potato genotypes. Darkened trichome exudates were observed on insects held on PI 473331 and PI 473334, consistent with prior reports that glandular trichomes of S. berthaultii contain phenolic oxidation chemistry.
Impacts
Feeding injury to potato by the potato leafhopper affects plant biomass accumulation by reducing the efficiency of use of captured solar radiation. E. fabae can cause major yield loss even before visual symptoms of feeding injury become obvious. Presently, insecticides provide the only effective means of controlling leafhoppers in conventional potato production. Because the economic threshold is very low (1 adult per 180-degree sweep or 1 nymph per 10 leaves), insecticides are usually used in a preventive manner. Leafhoppers are the major uncontrollable insect pest in organic potato culture because of the unavailability of insecticides or other effective management tactics. Our findings have characterized some of the potato leafhopper resistance mechanisms of S. berthaultii and its hybrids and while these results indicate that glandular trichomes may play a part in E. fabae resistance, follow-up studies in the presence vs. absence of glandular trichomes are needed to
clarify the role of pubescence in host acceptance. Additional efforts are also needed to identify specific molecular components of the resistance phenomena described here. Advances in this area will aid the commercial development of resistant cultivars by enabling a more efficient selection and evaluation of resistant genotypes in large populations of segregating progeny. The availability of leafhopper resistant cultivars will improve the viability of organic potato production and ultimately reduce or eliminate dependence on insecticides for management of this pest in conventional potato agriculture.
Publications
- Medeiros, A. H., I. Delalibera, Jr., & W. M. Tingey. 2005. Aspects of potato leafhopper (Homoptera: Cicadellidae) biology on Solanum berthaultii and other potato genotypes. J. Econ. Entomol. 98:
- Medeiros, A. H. De, W. M. Tingey, W. S. De Jong. 2004. Field evaluation of Solanum berthaultii inherited resistance to potato leafhopper (Empoasca fabae). Amer. J. Potato Res. 81:431-441.
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Progress 01/01/04 to 12/31/04
Outputs
Potato genotypes were evaluated for resistance to natural infestations of the potato leafhopper, Empoasca fabae (Harris) on the field. Characterization of type A and B glandular trichomes, phenolic properties of type A trichomes, glycoalkaloid content and composition, PLH adult and nymph population, leaf damage (hopperburn), yield and yield reduction were determined on the genotypes PI473331 and PI473334 (two accessions of Solanum berthaultii (Hawkes)), NY123 and Q174-2 (two advanced hybrids), and Elba and Allegany (two commercial cultivars). Regarding the Type A trichome, PI473334 was the most pubescent, followed by PI473331, both had high levels of enzymatic browning; on PI473334 no glycoalkaloids were detected, while on PI473331 solamargine and solasonine were present. Those genotypes were the least infested by PLH adults, moreover, nymphs were never found on their leaves. PI 473331 and Q174-2 possess Type B trichomes, the latter had levels of Type A trichome
comparable to the first and to NY123, while displaying high levels of phenolic oxidation of Type A and very low levels of glycoalkaloids. Although Q174-2 had intermediate infestation of E. fabae, it suffered a yield reduction comparable to the control cultivar, Allegany. The density of Type A trichomes of NY123 was relatively low, even though the browning assay results were significantly elevated. The foliage of this genotype was found to contain the four types of glycoalkaloids studied at high levels. The PLH infestation on NY123 was intermediate and it yielded well on infested plots, but suffered an intermediate yield reduction. Elba presented densities of type A similar to NY123. It suffered the lowest yield reduction despite its moderate levels of PLH infestation and hopperburn. High MEBA scores were correlated with high PLH infestation and high leaf damage. Results indicate a significant correlation between PLH infestation and hopperburn. Though factors other than glandular
trichomes are likely to be important, increased density of both types of trichomes and phenolic properties of Type A, along with reduced levels of solamargine and solasonine, are shown to be important to select in breeding for E. fabae resistance.
Impacts
Knowledge of the mechanisms by which plants defend against insect herbivory will aid in identification of specific genes responsible for resistance and may help accelerate development of resistant cultivars with built-in pest management qualities.
Publications
- Medeiros, A. H. De, W. M. Tingey and W. S. De Jong. 2004. Mechanisms of resistance to potato leafhopper, Empoasca fabae (Harris) in potato. Amer J of Potato Res. 81:431-441.
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