Management of field margins to maximize multiple ecological services
Published source details
Olson D.M. & Wäckers F.L. (2007) Management of field margins to maximize multiple ecological services. Journal of Applied Ecology, 44, 13-21.
Published source details Olson D.M. & Wäckers F.L. (2007) Management of field margins to maximize multiple ecological services. Journal of Applied Ecology, 44, 13-21.
Game strips on agricultural land can provide habitat and food for wildlife. This study investigated whether the benefits of field margins established for conservation of northern bobwhite quail Colinus virginianus extended to the enhancement of biological pest control in adjacent conservation tillage cotton fields. Densities of a selection of insect species and predation and parasitism rates of insect pest species were measured in first- and second-year field margins established for bobwhites, and in the adjacent cotton crop.
Focal insect species: Insect species sampled comprised potential bobwhite food: the noctuiids Helicoverpa zea, Heliothis virescens and Spodoptera spp. (sometimes serious cotton pests); Pseudoplusia includens (feeds on leaves of several plant species, including cotton); thrips (which damage seedling cotton); Aphis gossypii (commonest aphid in cotton); Lygus spp. (can damage cotton bolls); coccinellids (aphids are their main food); Orius insidiosus (important predators of many small-sized cotton pests); tachinids (larval-pupal parasitoids of many lepidopterans); Trichogramma spp. (minute egg parasitoids of primarily lepidopterans); and staphylinids (which feed on a variety of small insects and their eggs).
Over 2 years (2003-2004), insects were sampled in five cotton fields ( 23 to 45 ha in area) and 10 m wide bands of first- and second-year naturally occurring vegetation at their margins to provide bobwhite habitat. Three first- and three second-year margins were sampled. Sampling points (along transects) were 0 m (= field margin), 15 m, 45 m and 75 m from the margin. Plants in the field margins were identified and their density estimated.
Sticky strips: Yellow double-sided sticky strips (7.5 × 13 cm) were placed weekly on poles along the transects (again at 0, 15, 45 and 75 m from the margin) at the height of the cotton plants. Poles were raised as the cotton grew. Insects caught were identified and counted.
Cotton plant samples: Plants were randomly selected and examined weekly for herbivore larvae (5 June-1 August 2003, 7 plants; and 7 June-31 August 2004, 12 plants). Larvae were counted, and reared in a laboratory to assess parasitism rate. Due to small numbers of other species, analyses were carried out on Pseudoplusia includens only. In September each year, the number of bolls was counted on 21 randomly chosen plants at 15, 45 and 75 m from the margin and assessed for stinkbug damage and lepidoptera larvae. Parasitism levels of larvae were assessed.
Helicoverpa zea eggs: Each year irradiated H. zea eggs were placed on five cotton plants at each distance from themargin at each site, repeated on three dates in August each year , to estimate parasitism and predation rates. Single eggs were placed on a leaf near the plant top and left for 3 h. Eggs were collected and incubated to determine parasitism.
Field margin vegetation: In the first-year margins, the predominant tall (> 1 m) species was common ragweed Ambrosia artemisiifolia (60%), in second-year margins it was goldenrod Solidago canadensis (32%) and dogfennel Eupatorium capillifolium (17%).
Sticky strips: More thrips were found in the field than the field margins, with numbers higher at 45 and 75 m than 15 m from the field margin. More thrips were found in second- (average ± SD; 176 ± 285, n = 177) than first-year (105 ± 95, n = 168) margins in both years prior to cotton planting. More tachinids were found in second- than in the first-year field margins, with fewest in fields. The dominant species were Eucelatoria bryani (70%), Lespesia archippivora (11%) and Archytas marmoratus (9%).
More Aphis gossypii were found in fields than margins, none were found in the field margins prior to cotton planting. More Trichogramma spp. were found in field margins, their numbers were higher at 15 m than at 45 m and 75 m from the margin. Prior to cotton planting Trichogramma were more abundant in second- than in first- year margins. Coccinellids were more abundant in fields; only Harmonia axyridis was found in the field margins prior to cotton planting, and it was more abundant in second- than in first-year margins.
Pseudoplusia includens density was higher at 15 m than 45 m and 75 m from both the first- and second-year margins in 2003 and was higher at 15 m and 45 m than 75 m from second-year field margins in 2004. The 2004 effect was because of a field associated with a second-year field margin that had more larvae at 45 m than 75 m from the field margin. Staphylinids were more abundant in second- than in first-year fields in 2003, but they were more abundant in first- than in second-year fields in 2004. Prior to cotton planting in 2003, staphylinids were more abundant in second- (1.2 ± 1.3, n = 90) than in first-year field margins (0.5 ± 0.8, n = 84), and in 2004 they were more abundant in first- (2.2 ± 2.2, n = 84) than in second-year margins (1.1 ± 1.4, n = 87). More Lygus spp. were found in margins than fields in both years but they were more abundant in second- than first-year field margins in 2004. No Lygus was found in the field margins prior to cotton planting.
Cotton plant samples: Of the larvae found in 2003, 74% were P.includens (59/80), 19% H.zea and H.virescens (15/80) and 7% Spodoptera spp. (6/80). In 2004, 98% were P.includens (563/576), 2% H.zea (11/576) and 1% Spodoptera spp. (2/576). Combining both years, there were no differences in parasitism of P.includens collected on cotton (421 larvae) in first- (65/139 = 47%) and second- (138/282 = 49%) year margins (or age) and within the field regardless of distance away.
Helicoverpa zea eggs: There was no effect of margin age on the percentage of eggs parasitized or preyed upon (n = 675). However, the percentage of eggs parasitized was lower at 15 m (0%) than 45 m (54%) and 75 m (46%). The species reared from the eggs appeared all to be Trichogramma pretiosum. There was no effect of the percentage of eggs preyed upon across field locations (33%, 32% and 35% for 15 m, 45 m and 75 m from the margin, respectively).
Conclusions: Second-year field margins had higher densities of all insect species sampled, with the exception of staphylinids and cotton aphids. Overall, with regard to pest occurrence or biological control, the impact of second-year margins was similar to first-year margins. This study shows that field margins designed to specifically benefit bobwhite quail provide few other ecological benefits.