Section V: Potato Pests
TAKING A SECOND LOOK AT LYGUS BUGS IN THE PACIFIC NORTHWEST
Josephine Antwi, Silvia I. Rondon, Kenneth Frost, Aymeric Goyer, and Robert Cating
Oregon State University, HAREC 2121 1st St, Hermiston, Oregon, 97838
josephine.antwi@oregonstate.edu; silvia.rondon@oregonstate.edu;
kenneth.frost@oregonstate.edu; aymeric.goyer@oregonstate.edu; robert.cating@oregonstate.edu

This project is directed at enhancing our understanding of the epidemiology of the beetleafhopper transmitted virescence agent (BLTVA) by examining the ability of Lygus(Heteroptera: Miridae) bugs to transmit the pathogen to potato, Solanum tuberosum L. In theColumbia Basin of Washington and Oregon, BLTVA, a phytoplasma, is the primary cause ofpotato purple top disease and is known to be transmitted to potato primarily by the beetleafhopper (BLH), Circulifer tenellus Baker (Heteroptera: Cicadellidae). Plants infected withBLTVA usually express flagging of leaflets, leaves, small stems and swollen nodes. In thesummer of 2014, Lygus bugs were observed in the field in association with potato plants
expressing purple top symptoms. Currently, it is not known if Lygus bugs are competent vectorsof BLTVA. Reports from growers in the region also suggest a decline in the numbers of BLH in
potato fields while Lygus bugs are more abundant in potato fields than previous years. Thus, thepresent study evaluated: (1) the abundance and species composition of Lygus bugs in commercial
potato in the PNW, (2) the incidence of BLTVA in Lygus in commercial potato fields and (3)whether Lygus harbors the same strain of BLTVA as symptomatic potato plants.
Materials and Methods
In 2015, Lygus were collected from 34 potato fields in Oregon using a hand-held inverted leaf
blower. Samples were collected at three time points: early, mid, and late season and the total
number of Lygus bugs were estimated for each location. Samples were sorted and identified
using the dichotomous key developed by Muller et al. (2003). Based on the 16S rRNA gene, weused the nested PCR technique described by Crosslin et al. (2006), to estimate the incidence ofBLTVA in field-collected Lygus. PCR products were visualized on 1% agarose gel to confirm
the presence of BLTVA. To determine if Lygus harbors the same strain of BLTVA as
symptomatic potato plants, we cloned PCR products from Lygus and potato samples, sequenced
both products then compared DNA sequences of BLTVA from Lygus and potato. Comparing
BLTVA sequences from both Lygus and potato allows us to determine if Lygus is carrying thesame BLTVA as symptomatic potato and whether or not we should worry about Lygus aspotential vectors of BLTVA.

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Results and Discussion
Morphological identification: In Oregon, the Lygus complex in potato is dominated by Lygus
hesperus, L. elisus and L. lineolaris (Figs. 1A, B, and C). The 3 species are primarily
distinguished by the unique pattern of frons, pronotum and wing membrane as well as thepresence/absence of spots on the propleura (side of the pronotum).

Fig. 1 Three major Lygus species identified in potato fields in the Columbian Basin in Oregon. Photo by OSU-IAEP(Rondon lab by J. Antwi).

Lygus population dynamics: In general a total of 240, 358 and 127 Lygus were collected inJune July and August, respectively (Fig. 2). Across all sampling sites, we collected an averageof 7 Lygus per location; where the highest average (42 Lygus per site) occurred at location 14and lowest average (1 Lygus per site) occurred at location 12 (see map and location of traps athttps://andersongeog.maps.arcgis.com/apps/webappviewer/index.html?id=e857a721431642188f
a27b04c2f7c270. All Lygus were tested for BLTVA; 0, 25, 36 and 12 % of the samples tested
positive in May, June, July and August, respectively (Fig. 3).

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BLTVA in potato and Lygus: 16S DNA sequences of BLTVA showed that field-collectedLygus carry/harbor the same strain of BLTVA in symptomatic potato (data not shown),suggesting that Lygus is acquiring and/or transmitting BLTVA to potato. A preliminarytransmission assay demonstrated that BLTVA can indeed be transmitted by Lygus (unpublisheddata); however the mode of the transmission and the efficiency is unknown. We are currently
undertaking more studies to further our understanding of the interaction between Lygus andBLVTA and whether or not Lygus bugs cause significant economic damage to potato.
The role of Lygus and its associated impact on potato production are unknown and need to befurther investigated. If Lygus is a pest of potato, then, there is a strong need to focus our attention
towards this problem.
References
Mueller, Shannon C., Charles G. Summers, and Peter B. Goodell. 2003. "A field key to the mostcommon Lygus species found in agronomic crops of the central San Joaquin Valley ofCalifornia." Univ. Calif. Agric. Nat. Res. Publ. 8104: 11.
Crosslin, J. M., G. J. Vandemark, and J. E. Munyaneza. 2006. "Development of a real-time,quantitative PCR for detection of the Columbia Basin potato purple top phytoplasma inplants and beet leafhoppers." Plant Disease 90.5: 663–667.

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