ELECTROPHORETIC ANALYSIS OF ORIUS INSIDIOSUS (HEMIPTERA : ANTHOCORIDAE) FEEDING HABITS IN FIELD CORN

Abstract

The feeding habits of the hemipteran predator Orius insidiosus were studied over a period of several weeks in Northwest Kansas field corn using gel electrophoresis. The banding patterns of the starved predator and 6 different potential food items of the predator were determined for the enzyme isocitrate dehydrogenase. Field collected predators were then analyzed with electrophoresis to determine the food items present in their gut. Sampling was done in three different fields once per week for 10 weeks during 1992 and once a week for 8 weeks during 1993. Our results indicated that early in the season (early to mid-June) be fore tasseling of corn, the predominant food item of O. insidiosus was flower thrips. During late June and early August, O. insidiosus fed mostly on corn pollen. Corn leaf aphids, leafhop pers and eggs and first instar larvae of the European corn borer and the corn earworm were utilized as food at relatively low levels. Late in the season (mid-August to early September), a food item that we could not identify, but suspect to be corn kernels, was detected in the predator's gut. Our results suggested that (1) O. insidiosus did not frequently consume the eggs or the first instar larvae of the European corn borer or corn earworm in corn, and (2) electrophoresis is a suitable method for studying the feeding habits of field-caught predators. The insidiosus flower bug, Orius insidiosus (Hemiptera: Anthocoridae), is a preda ceous insect found on field crops in the midwestern United States (Isenhour et al., 1990). Orius insidiosus is a polyphagous predator which feeds on plant and arthro pod material allowing it to persist in a variety of habitats (Kiman and Yeargan, 1985). Orius insidiosus often occurs in corn, Zea mays, and is abundant during pollen shed and silking (Corey, 1994). Its presence in corn fields coincides with eggs of the sec ond generation European corn borer (ECB), Ostrinia nubilalis, and corn earworm (CEW), Heliothis zea (Isenhour and Marston, 1981; Isenhour and Yeargan, 1981; Coll and Botrell, 1991). Orius insidiosus nymphs and adults consume eggs and first instar larvae of ECB and can complete development on an exclusive diet of ECB eggs (Andow, 1990). In field tests, in the absence of other prey and predators, fewer corn borer and corn earworm larvae emerge after exposure to O. insidiosus (Reid, 1991). Because ECB is an important pest of corn in the United States, the extent of pr?dation by O. insidiosus on ECB eggs is of interest to integrated pest management programs. Food habits of individual predators may be determined by direct observation in the field or in the laboratory. The drawbacks of a laboratory-based approach include labor-intensive nature, artificiality of the environment, and non-applicability to cer tain arthropod groups (Lister et al., 1987). In some cases recognizable prey remains may be identified in the gut of predators that chew their food (Sunderland, 1975; Phillips, 1981), but in predators with a liquid diet, such as the Hemiptera, more so phisticated techniques may be required (Giller, 1984). An important development has been the study of feeding habits of individual predators by electrophoretic analysis of prey remnants inside their gut. Using elec trophoresis, Murray and Solomon (1978) determined that the anthocorid, Anthocoris Accepted for publication 20 June 1998. This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:03:52 UTC All use subject to http://about.jstor.org/terms 12 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY nemoralis, preferred the aphid, Pterocallis alni, over the alder sawfly, Fenusa dohrnni. Similarly, Skinner (1983) identified the feeding preferences of A. nemoralis for aphids and psyllids in apple orchards. The above studies and others like them (see Corey, 1994) suggested that the use of electrophoresis to study the food habits of field-collected predators could provide information that is important in the con text of integrated pest management. Furthermore, a study that includes an examina tion of temporal dynamics of predator feeding throughout a growing season is likely to provide an indication of the predator's potential as a biological control agent, given its response to various food items available at any given time. Therefore, the objective of this study was to determine, using electrophoresis, the feeding habits of field collected O. insidiosus through an extended period of the growing season. Materials and Methods field sampling of o. insidiosus and its prey: Studies were conducted in Riley County, KS, during 1992 and 1993 in two commercial corn fields and one corn field at the Kansas State University (KSU) Agricultural Experiment Station. The plots were selected because of their proximity to alfalfa and soybean which act as refugia for O. insidiosus before the migration of predators to corn (Isenhour and Marston, 1981). The corn was grown without the use of insecticides. During 1992, the two commercial study sites were approximately 55 m x 67 m in area and the KSU plot was 27 m x 33 m. During 1993, the dimensions of the two commercial plots were 80 m x 60 m and that of the KSU plot 27 m x 42 m. Weekly sampling commenced on July 1, 1992 and June 9, 1993 and ended in late August or early September, when corn plants generally did not contain O. insidiosus. Sampling was performed at approximately 7 a.m. Corn plants were cut with garden shears, placed in large plastic bags along with a tag to identify the field and location and placed in a refrigerator for 2 hr. Immature and adult O. insidiosus were counted and a minimum of three individuals from dif ferent parts of each plant were placed in prenumbered vials and their location on the plant was noted. The vials were stored at -70?C until use. The presence of ECB egg masses, corn leaf aphids (CLA), Rhopalosiphum maidis, corn earworm (CEW) eggs and larvae, leafhoppers, grass thrips, Anaphothrips obscurus, and other possible prey was recorded but not quantified. electrophoretic analysis of field collected o. insidiosus: Prey remnants in the guts of individual predators were identified by means of poly aery lamide gel elec trophoresis (PAGE) of enzyme loci using a Hoefer Scientific SE600 system. Initially, laboratory reared and starved O. insidiosus immatures and adults, ECB eggs and 1st instar larvae, CEW eggs and 1st instar larvae, CLA, corn pollen, silks, and anthers, thrips, spider mites, Tetranychus urticae, adult and nymphal leafhoppers were ho mogenized individually in 40 |Lil of buffer (10% sucrose, 0.01% bromphenol blue, 1% Triton X-100 dissolved in tris-citrate electrode buffer) and examined for enzy matic activity as described by Kambhampati et al. (1990). Eight enzyme systems, viz., glucose 6-phosphate dehydrogenase, isocitrate dehydrogenase, esterase, phos phoglucoisomerase, lactate dehydrogenase, phosphogluco mutase, malic enzyme, and alkaline phosphatase were examined with two different buffer systems: tris borate-EDTA (0.81 M Tris, 0.2 M boric acid and 15 mM EDTA, pH 8.9) and tris citrate (0.78 M Tris, 0.24 M monohydrate citric acid, pH 7.1). Sensitivity tests were This content downloaded from 207.46.13.114 on Thu, 26 May 2016 06:03:52 UTC All use subject to http://about.jstor.org/terms