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Surveys of Lygus spp. and their Movement on Cultivated Crops and Non-cultivated Habitats throughout Growing Season in Colorado



N. Demirel and W. Cranshaw
 
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ABSTRACT

A three-year survey was conducted to evaluate population density and movement of Lygus species on cultivated crops and non-cultivated habitats throughout the growing season in Colorado. Three Lygus species, L. elisus, L. hesperus, L. lineolaris, were commonly found in cultivated crops and non-cultivated habitats based on concurrent adult collections in Colorado. Lygus species were found from early April to late in August, having multiple generations in each year in Colorado. Lygus species had wide host range in Colorado. Alfalfa was a significant host plant for Lygus species. However, after cutting alfalfa, Lygus species moved to adjacent crops, i.e. canola and caused significant injury during early flower and pod stages. The wild mustards, flixweed, D. sophia L. and tansy mustard, D. pinnata (Walt.), were significantly important host plants in non-cultivated areas and within cultivated crops. Removing wild mustard in sampling area resulted in the movement of Lygus species to canola crop. In conclusion, it might be important to know population density of Lygus species and their movement on cultivated crops and non-cultivated habitats to predict their injury to canola plants to develop control strategies.

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  How to cite this article:

N. Demirel and W. Cranshaw, 2006. Surveys of Lygus spp. and their Movement on Cultivated Crops and Non-cultivated Habitats throughout Growing Season in Colorado. Pakistan Journal of Biological Sciences, 9: 197-200.

DOI: 10.3923/pjbs.2006.197.200

URL: https://scialert.net/abstract/?doi=pjbs.2006.197.200

INTRODUCTION

The genus Lygus Hahn (Hemiptera: Miridae) contains plant bugs including several economically important species in the United States (Schuh and Slater, 1995; Wheeler, 2000; 2001). Worldwide there are 43 known species of Lygus (Kelton, 1975) with 34 presents in the United States (Kelton, 1975). Most Lygus species are multivoltine (Henry and Lattin, 1987; Kelton, 1975; Layton, 2000) and all Lygus species overwinter as adults (Kelton, 1975; Layton, 2000; Wheeler, 2000). Most Lygus species are oligophagous (Henry and Lattin, 1987; Kelton, 1975; Schuh and Slater, 1995; Wheeler, 2000). They are highly mobile and annually migrate to crop areas (Kelton, 1975). Three Lygus species were important in cultivated crops and non-cultivated habitats in Colorado: L. elisus Van Duzee, the pale legume bug; L. hesperus Knight, the western tarnished plant bug; L. lineolaris (Palisot de Beauvois), the tarnished plant bug (Demirel et al., 2005; Kelton, 1975). However, little known about their biology outside the croplands which might be critical for development of their population density and their movement (Demirel et al., 2005). The purposes of this study were to evaluate their population density and their movement on cultivated crops and non-cultivated habitats throughout the growing season in Colorado.

MATERIALS AND METHODS

A total of twenty-two different Colorado sites were sampled during 2000, 2001 and 2002 in Larimer (LC), Western Weld (WWC) countries. Thirteen sites (6 LC, 7 WWC) in 2000, ten sites (5 LC, 5 WWC) in 2001, and thirteen sites (10 LC, 3 WWC) in 2002 were sampled (Table 1). Field sampling involved using a standard 15-in diameter sweep-net, taking 20 sweep net samples per site for each sampling. Samples were taken from 18 April to 2 August in 2000, 18 April to 14 August in 2001 and 18 April to 13 August in 2002.

Samples were taken from varieties of vegetation types including croplands primarily monocultures of alfalfa (Medicago sativa L.), which sometimes infested with flixweed (Descurainia sophia (L.) Webb ex Prantl, and roadsides containing tansy mustard (Descurainia pinnata (Walt.).

Table 1:
Sites used in surveys of Lygus spp. on varies habitats at LC and WWC in Colorado in 2000-2001- 2002
1 Flixweed at H257 B was predominantly the native species, Descurainia pinnata (Walt.) Britt. Flixweed at all other sites was predominantly the introduced European species, Descurainia sophia (L.) Webb. ex Prantl

Having flixweed common throughout the field, alfalfa fields were described as "some flixweed". Fields where flixweed present but uncommon, were described as "little flixweed". All samples were taken between 10 AM to 4 PM to allow warming on the surface of plants. Samples were taken by the same person, usually on a straight line transect across the sampling site. Samples were immediately placed into plastic bags and returned to the lab for counting of Lygus spp. nymphs and adults.

RESULTS AND DISCUSSION

Based on concurrent adult collections, three Lygus species, L. elisus, L. hesperus, L. lineolaris, were commonly found in cultivated crops and non-cultivated habitats in Colorado. The great majority of Lygus spp. present were L. elisus, L. hesperus, a small percentage of the adult insects were L. lineolaris in samples sites. Moreover, the most recent Lygus survey in 2002 resulted in three species present within different percent in Colorado (Demirel et al., 2005). Lygus elisus was recovered with the highest frequency at 58.4 % of all. Lygus hesperus was the second most abundant species (29.3 %) followed by L. lineolaris (12.3%) (Demirel et al., 2005).

The greatest numbers of Lygus species were recovered in 2000 with 2 times and 2.9 times greater total capture than those of 2001 and 2002, respectively (Table 2-4). The population density of Lygus species had a couple of peaks during sampling period; 7 June 2000, 7 June and 21 July in 2001 and 18 May and 22 July in 2002, respectively. The first Lygus species were reported in each year in the middle of April. This support previous report by Kelton (1975) indicating the movement of Lygus species from winter shelter by early spring. In addition, Lygus species were also found more consistently throughout the season. The most recent survey also indicated that activity of Lygus species was continued into October (Demirel et al., 2005). Furthermore, different Lygus species had different activity periods. For example, in 2002, 1745 Lygus adults were collected in total and the highest population of L. elisus occurred during the early season which comprised 98.0 and 89.2% of all Lygus collected in May and June samplings, respectively (Demirel et al., 2005). Lygus hesperus tended to occur in higher ratio later in the season becoming the predominant Lygus species during October and September. Moreover, the greatest recoveries of L. lineolaris were in July and October, with none collected in August (Demirel et al., 2005).

The current survey indicated that alfalfa was a favored food source of three Lygus species in Colorado as mentioned previous studies (Sevacherian and Stern, 1974; 1975). For example, Lygus species had the highest population density in alfalfa fields at CR15 C in 9 May, Ardec D in 16 May, H257 A in 17 May, Severance B, EI25, Hortfarm, and W. cargill in 7 June in 2000, Ardec E, F, EI25, CR15 C and W. cargill in 29 May, Hortfarm, H257 C in 7 June in 2001, Ardec C, CR15 C, EI25, W. cargill in 18 May, Hortfarm in 18 June in 2002 (Table 2-4).

Table 2: Weekly samples of Lygus spp. on varies habitats at LC and WWC in Colorado in 2000

Table 3: Weekly samples of Lygus spp. on varies habitats at LC and WWC in Colorado in 2001

Table 4: Weekly samples of Lygus spp. on varies habitats at LC and WWC in Colorado in 2002

However, after cutting alfalfa, the population density of Lygus species had a sharp decline in sampling sites. For example, the population density of Lygus species declined after cutting alfalfa at those sampling places; CR 15 C in 16 May, Ardec D, H257 A in 23 May, Severance B in 7 June, EI25, W. cargill in 14 June, Hortfarm in 21 June in 2000, Ardec E, EI25 in 7 June, Hortfarm, H257 C in 12 June in 2001, Ardec C, CR15 C, EI25, and W. cargill in 27 May in 2002 (Table 2-4). This suggests that alfalfa harvest contributes to Lygus migration. Moreover, previous report by (Demirel, N., 2003, Ph. D Thesis, Colorado State University) indicated that after cutting alfalfa, the Lygus species moved to canola crops and caused significant injury, especially during early flower and pod stages. However, previous report indicated that manipulations of alfalfa through strip harvest can prevent migration of Lygus to adjacent crops (Stern et al., 1964; Stewart and Layton, 2000).

Lygus species were commonly found on flixweed in early season. For example, the sampling sites, Ardec A, Ardec B, CR15 B, H257 B, Severance A sites in 7 June in 2000 and H257 B, Severance A sites in 29 May in 2001 with flixweed alone, had higher Lygus populations (Table 2 and 3). In addition, the previous survey also indicated that the Lygus species might be found at different percentages in different vegetations sampled (Demirel et al., 2005). Lygus elisus was found mainly on flixweed and in alfalfa/flixweed mixtures. Lygus hesperus was the species most commonly recovered from lambsquarters, Chenopodium album L., kochia, Kochia scoparia (L.) Schrad. and pigweed, Amaranthus retroflexus L. in Colorado (Demirel et al., 2005). However, after removing flixweed in sampling areas the population density of Lygus species decreased, i.e., Ardec A and B, H257 B, and Severance A in 14 June, CR 15 B in 21 June in 2000, H257 B 7 June in 2001 (Table 2 and 3).

In conclusion, three Lygus species, L. elisus, L. hesperus, L. lineolaris, were important pests in cultivated crops and commonly found in non-cultivated habitats in Colorado. Lygus species having multiple generations per year were found from early in April to late in August in Colorado. Lygus species have a wide host range. Alfalfa was significant host plant for Lygus species and yet after cutting alfalfa, Lygus species moved to adjacent canola and caused significant injury during early flower and pod stages. The wild mustard, flixweed, D. sophia L., and tansy mustard, D. pinnata (Walt.), were important host plants in the non-cultivated and within cultivated crops in Colorado. Removing of wild mustard in sampling areas also caused the movement of Lygus species to canola crop in Colorado. Strip cutting, where strips of alfalfa is cut alternately to prevent the movement of Lygus spp. from alfalfa to canola, managing cutting times of alfalfa before or after the flower and pod stages of canola, but more importantly not to plant alfalfa and canola to adjacent fields might be useful tactics to decrease the Lygus injury on canola crops. In addition, wild mustards around the field can be destroyed to prevent the population build up of Lygus spp.

ACKNOWLEDGMENTS

We would like to give so special thanks to all the farmers and the Cargill Oilseed Research Center who gave me permission to take samples in their field. This project was supported by Colorado Agricultural Experiment Station. ND was supported by the Ministry of National Education of Republic of Turkey.

REFERENCES
1:  Demirel, N., W. Cranshaw and A. Norton, 2005. Survey of Lygus spp. and an associated parasitoid, Leiophron uniformis (Gahan), in Colorado. Southwestern Entomologist, 30: 9-15.

2:  Henry, T.J. and J.D. Lattin, 1987. Taxonomic Status, Biological Attributes and Recommendations for Future Work on the Genus Lygus (Heteroptera: Miridae). In: Economic Importance and Biological Control of Lygus and Adelphocoris in North America. Hedlund, R.C. and H.M. Graham (Eds.). USDA-ARS Pub., Beltsville, Maryland, pp: 95.

3:  Kelton, L.A., 1975. The Lygus bugs (Genus Lygus Hahn) of North America (Heteroptera: Miridae). Mem. Entomol. Soc. Can., 95: 1-101.

4:  Layton, M.B., 2000. Biology and damage of the tarnished plant bug, Lygus lineolaris, in cotton. Southwestern Entomol., 23: 7-20.

5:  Stern, V.M., R. Van Den Bosch and T.F. Leigh, 1964. Strip cutting alfalfa for Lygus bug control. Calif. Agric., 18: 4-6.

6:  Sevacherian, V. and V.M. Stern, 1974. Host plant preferences of Lygus bugs in alfalfa-interplanted cotton fields. Environ. Entomol., 3: 761-766.

7:  Sevacherian, V. and V.M. Stern, 1975. Movements of Lygus bugs between alfalfa and cotton. Environ. Entomol., 4: 163-165.

8:  Schuh, R.T. and J.A. Slater, 1995. True Bugs of the World (Hemiptera: Heteroptera): Classification and Natural History. Comstock Publication Associates, Ithaca, New York, pp: 336.

9:  Stewart, S.D. and M.B. Layton, 2000. Cultural controls for the management of Lygus populations in cotton. Southwestern Entomologist. Suppl., 23: 83-95.

10:  Wheeler, Jr. A.G., 2000. Plant Bugs (Miridae) as Plant Pests. In: Heteroptera of Economic Importance, Schaefer, C.W. and A.R. Panizzi (Eds.). CRC Press, Boca Raton, London, New York, Washington, DC., pp: 37-83.

11:  Wheeler, Jr. A.G., 2001. Biology of the Plant Bugs (Hemiptera: Miridae) Pests, Predators, Opportunists. 1st Edn., Cornell University Press, Ithaca, New York.

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