University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications: Department of Entomology Entomology, Department of 7-2006 Effects of Aphid (Homoptera) Abundance and Surrounding Vegetation on the Encounter Rate of Coccinellidae (Coleoptera), Chrysopidae (Neuroptera), and Nabidae (Hemiptera) in Alfalfa James C. Kriz University of Kansas Stephen D. Danielson University of Nebaska–Lincoln, [email protected] James R. Brandle University of Nebraska-Lincoln, [email protected] Erin E. Blankenship University of Nebraska-Lincoln, [email protected] Geoff M. Henebry South Dakota State University, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/entomologyfacpub Part of the Agronomy and Crop Sciences Commons, and the Entomology Commons Kriz, James C.; Danielson, Stephen D.; Brandle, James R.; Blankenship, Erin E.; and Henebry, Geoff M., "Effects of Aphid (Homoptera) Abundance and Surrounding Vegetation on the Encounter Rate of Coccinellidae (Coleoptera), Chrysopidae (Neuroptera), and Nabidae (Hemiptera) in Alfalfa" (2006). Faculty Publications: Department of Entomology. 614. http://digitalcommons.unl.edu/entomologyfacpub/614 This Article is brought to you for free and open access by the Entomology, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications: Department of Entomology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Effects of Aphid (Homoptera) Abundance and Surrounding Vegetation on the Encounter Rate of Coccinellidae (Coleoptera), Chrysopidae (Neuroptera), and Nabidae (Hemiptera) in Alfalfa 1 2 3 4 5 James C. Kriz , Stephen D. Danielson , James R. Brandle , Erin E. Blankenship , and Geoff M. Henebry6 Department of Entomology, 202 Pl Bldg. , University of Nebraska, Lincoln, Nebraska 68583-0816 USA J. Entomol. Sci. 41 (3): 211-220 (July 2006) Abstract Predaceous insect encounter rate was measured in 21 southeast Nebraska alfalfa fields through weekly sweep net sampling during 2002-03. The most frequently encountered predaceous insect families were Coccinellidae (Coleoptera), Nabidae (Hemiptera), and Chrysopidae (Neuroptera). The study used multiple regression analysis to examine the effect of aphid abundance and the surrounding vegetative patch composition on predaceous insect abun­ dance. In 2002, Hippodamia parenthesis Say was encountered more frequently in fields with lower aphid abundances, and Hippodamia convergens Guerin-Meneville, Coccinella septem­ punctata L., and Nabis americoferus Carayon were encountered more frequently in fields with higher aphid abundances. In 2003, Coleomegilla maculata DeGeer was encountered more frequently in fields with higher aphid abundance. The remaining two species of coccinellids and Chryoperla spp. did not exhibit significant correlations with aphid abundance in either year. It was determined that in 2002, H. parenthesis was encountered more frequently in alfalfa sur­ rounded by a higher percentage of unfarmed land, and C. maculata, C. septempunctata, N. americoferus, and Chrysoperla spp. were encountered more frequently in alfalfa surrounded by a higher percentage of farmed land. In 2003, N. americoferus was again encountered more frequently in alfalfa fields surrounded by a higher percentage of farmed land. The remaining three coccinellid species collected did not exhibit significant relationships between vegetative patch composition and encounter rate in either year. Key words alfalfa, Aphididae, Coccinellidae, Nabidae, Chrysopidae, patch composition, Shannon Evenness Index, conservation biological control Damage caused by Aphididae (Homoptera) can significantly reduce the quantity and quality of alfalfa, Medicago sativa L. (Danielson et al. 1993). When aphid infes­ tations reach levels of economic significance, the producer typically applies a pesti­ cide to the field (Danielson et al. 1993). Current integrated pest management trends 'Received 21 October 2005; accepted for publication 15 May 2006. 2 University of Kansas, Lawrence, Kansas, Central Plains Center for Bioassessment. 3 University of Nebraska, Lincoln, Nebraska, Department of Entomology; Address inquiries (email: sdanielson1 @unl.edu). 4 University of Nebraska, Lincoln, Nebraska, School of Natural Resources Science. 5 University of Nebraska, Lincoln, Nebraska, Department of Statistics. 6 South Dakota State University, Brookings, South Dakota, Geographic Information Science Center of Excel­ lence. 211 212 J. Entomol. Sci. Vol. 41 , No. 3 (2006) aim to reduce the amount of pesticides applied to reduce both expense and environ­ mental perturbation. Previous work has shown that conservation biological control techniques have the potential to be used to manipulate predaceous insect populations and possibly control aphid infestations (Honek and Hodek 1996, Ferro and McNeil 1998, Landis et al. 2000). Studies have shown the vegetative landscape structure can influence coc­ cinellid abundance in agricultural landscapes (Colunga-Garcia et al. 1997, Elliott et al. 1998, 2002a, b) . Successful application of conservation biological control tech­ niques is dependent upon an understanding of how aphid abundance and the sur­ rounding vegetative patch composition may affect predatory insect abundance within the field. This study investigated the relationship between aphid abundance and vegetative patch composition and predator abundance using patch analysis, a tool of landscape ecology. Methods and Materials During 2002 and 2003, 21 alfalfa fields in Butler and Seward counties, NE, USA, were sampled weekly from the second week of May through the first week of August. Only fields containing 2:75% pure alfalfa stands were sampled. This was measured at the beginning of each field season by visually examining 4 approx. 40 x 40 m randomly selected plots within each alfalfa field. If any of these plots contained <75% pure alfalfa the entire field was examined to determine if the entire field fell below this threshold. This analysis was done to reduce the effects of within-field vegetative diversity by ensuring that the fields being sampled were primarily pure alfalfa. Sampling was conducted during late morning and afternoon when the alfalfa was not wet from either morning dew or rain and the air temperature was 2: 15.5°C. Alfalfa fields that were recently harvested or <15 cm in height were not sampled, because at canopy heights <15 cm the insect population is greatly reduced and was assumed to be negligible for the purposes of this study. Pesticides were not applied to the study fields during the sampling periods. These collection guidelines were similar to those of Kieckhefer et al. (1992) and Wright and DeVries (2000). Sampling was conducted using a 38-cm diam sweep net with a canvas bag, and sweeping was performed as close to the ground as possible given the height of the alfalfa. Four subsamples of 50 sweeps were taken along randomly chosen transects in a randomly chosen direction for a total of 200 sweeps per weekly sampling event per field. Sweep net sampling was chosen based on Fenton and Howell (1957) and Pruess et al. (1977) who observed that sweep net sampling provided reliable esti­ mates of both total and relative abundance of predatory insects in alfalfa. Schotzko and O'Keeffe (1989) found that sweep net sampling could be used to obtain estimates of the relative abundance of Coccinellidae (Coleoptera), Nabidae (Hemiptera), and Chrysopidae (Neuroptera) in a variety of leguminous crops including alfalfa. Samples were frozen, sorted, and the number and species of adult coccinellids and adult and larval nabids were recorded. The number of adult and larval chrysopids and larval coccinellids was recorded, but they were not identified beyond genus due to taxo­ nomic difficulties and lack of appropriate taxonomic keys. Members of the coccinellid genus Cycloneda were not identified to species because of taxonomic difficulties with the group. Aphid abundance was measured by counting all the aphids in one quarter of each 50 sweep subsample. The counts were converted into an aphid index that ranged KRIZ ET AL. : Impacts on Aphid Predator Encounter Rates 213 from 0-4 with 0 assigned to a subsample containing no aphids, 1 assigned for 1-10 aphids, 2 for 11-100 aphids, 3 for 101-400 aphids, and 4 for subsamples containing >400 aphids. The mean of the four subsamples was used as the sample aphid index, and the sample aphid index was used in the analysis. Vegetative landcover characteristics surrounding each field were mapped, using aerial photographs, within a radius of approx. 1.61 km from the centroid of each alfalfa field. The data from these maps were used to create digital maps using Digital Or­ thophoto Quarter Quadrangles (DOQQ) and ArcView GIS 3.0 (ESRI 2001 ). Similar to Jansen and Fahrig (1997) and Elliott et al. (1998, 2002a, b) , the landscape was classified into the vegetative categories: other alfalfa (alfalfa other than the sampled field) , Conservation Reserve Program (CRP) and meadow, pasture, cropland [means for 2002-03 (annual means were not significantly different at alpha= 0.05), corn (51 % of the total cropland), soybean (47%), wheat (<1 %), oats (<1 %), rye (<1 %), and grain sorghum (<1 %)] , and the sampled alfalfa field . These landcover vegetation types were designated on the digital maps inside an oval, the outer edge of which was 500 m (±5 m) from the centroid of each sampled alfalfa field. The 500 m distance was based