Ability of Orius insidiosus (Hemiptera: Anthocoridae) to Search for, Find, and Attack European Corn Borer and Corn Earworm Eggs on Corn CRAIG D. REID Illinois Natural History Survey and University of Illinois, Urbana, Illinois 61820 J. Econ. Entomol. 84(1): 83-86 (1991) ABSTRACT The ability of Orius insidiosus (Say) to search for, find, and destroy eggs of Downloaded from https://academic.oup.com/jee/article/84/1/83/2215498 by guest on 25 September 2021 European corn borer, Ostrinia nubilalis (Hiibner), and corn earworm, Helicoverpa zea (Boddie), was investigated in the field. Mobility of O. insidiosus on individual corn plants, attack rates on corn borer and corn earworm eggs, and searching capacity on corn plants were studied. Egg position on the corn plant and predator density affected egg mortality. Mortality rates rose with increased predator numbers. O. insidiosus searched in the corn silks first, followed by searching on the corn leaves but not in the tassel. KEY WORDS Insecta, Orius insidiosus, searching capacity, corn THE EUROPEAN CORN BORER, Ostrinia nubilalis from the cages, and the cage bottoms were sealed (Hubner), and the corn ear worm, Helicoverpa zea with soil. Each plant was treated with malathion (Boddie), are important pests of corn (Luckman (mixture of 2 ml of malathion in 500 ml of water) 1979). Onus insidiosus (Say), the insidious flower 2 d before the experiments started to remove un- bug, is a polyphagous predator that has been ob- wanted predators and prey. served to feed on the eggs of the corn borer (Jarvis Adults of O. insidiosus were field-collected in & Guthrie 1987) and the corn ear worm (Barber alfalfa and maintained on eggs of the soybean loop- 1936). The fact that O. insidiosus has been reported er, Pseudoplusia includens (Walker), in clear plas- to feed on corn borer and corn ear worm eggs could tic 500-ml containers (9 cm diameter, 7 cm deep) make it a candidate for augmentative biological with a large organdy-covered hole in the lid. Corn control against these pests. borer eggs were collected from sweet corn fields According to Huffaker et al. (1987), when a just before testing. Corn earworm eggs were ob- predator is being considered for augmentation, it tained from a laboratory colony which was main- is important to study and evaluate the predator's tained as described by Waldbauer et al. (1984). searching capacity for the prey as well as the preda- Corn borer and corn earworm egg distribution on or's general mobility. Hassell (1978) states that the the corn plant was designed to mimic natural con- ability of a predator to affect the prey population ditions. depends on the number of predators present and For corn ear worm tests, a total of :::::;150 eggs their capacity for finding and consuming prey. attached to cheesecloth were cut into six strips The purpose of this study was to investigate the ranging from 18 to 30 eggs per strip. Corn earworm ability of O. insidiosus to search for, find, and eggs are laid mostly in the silks and occasionally destroy corn borer and corn earworm eggs under on the tassels and leaves (Kuhlman 1983). There- field conditions. Prey egg density was kept at a fore, egg strips were attached by small paper clips constant level to show that increases in predation to the following six positions: silks, three; tassel, were due to an increase in predator density and two; uppersides of leaves above the ear, one. were not a result of an increase in prey density. Corn borer egg masses are usually laid on the ear husk and on the upper or lower side of the leaves near the ear (Kuhlman 1983, Showers et al. 1983). Six egg masses (:::::;150eggs) were attached Materials and Methods by No.3 insect pins onto the following six positions The capacity of O. insidiosus to search for and for the corn borer tests: ear, two; uppersides of consume corn borer and corn ear worm eggs was leaves, above the ear, two; undersides of leaves investigated on field corn. All tests were run at the below the ear, two. University of Illinois Pomology Orchards, Urbana, For corn earworm and corn borer tests, O. in- Ill., between 8 July and 14 August 1987. sidiosus adults (0 [check], 1,3,6, or 12) were placed Wood-framed, 400-mesh, drapery-sheer cages (3 on the lower leaves of the corn plant; i.e., away by 1.4 by 1.4 m) were placed over individual field from the location of the eggs of the prey. Each corn plants. Weeds and other plants were removed predator density was repeated three times. 0022-0493/91/0083-0086$02.00/0 © 1991 Entomological Society of America 84 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 84, no. 1 Table I. Effect of O. insidiosus on total percentage of Table 3. Effect of O. insidiosus on the percentage mor- corn borer eggs destroyed in 48 h tality of the mean number of corn borer eggs attached to different parts of the com plant Predator density Total % eggs destroyed, f ± SEMa Ears Leaves o 14.80 ± O.33a 1 19.10 ± O.33b Predator i i iNo. f No. 3 28.66 ± 3.83c denSity Egg Egg eggs % eggs % 6 36.00 ± 3.27d mortality mortality 12 53.33 ± 5.35e 0 53.0 16.70aA 96.3 15.83aA 1 51.3 15.17aB 93.3 24.12bA Means in the same column followed by the same letter are not 3 53.7 14.37aB 95.0 37.12cA significantly different (F 54.3; df 3, 8; P 0.05; one-way = = = 6 47.7 16.77aB 88.7 55.65dA ANOV A with SNK tests for multiple comparisons [Sokal & Rohlf 12 44.7 16.44aB 90.7 80.17eA 1981]). Downloaded from https://academic.oup.com/jee/article/84/1/83/2215498 by guest on 25 September 2021 a All means and standard errors are based on three replications of six egg masses ('" 150 eggs per plant). Mean numbers of eggs attached and mean percentages of mor- tality are based on three replicates. Mean percentages in the same column followed by the same letter and means in the same row followed by the same capital letter are not significantly different (P = 0.05; one-way ANOVA with SNK tests for multiple com- All field-collected adults were provided with wa- parisons [Sokal & Rohlf 1981]). ter but were starved 24 h before testing. All tests started between 1430 and 1530 hours (CDST), and egg masses or strips were retrieved 48 h later. Re- trieved eggs were then held at 37°C until hatch to Two-way ANOV A showed that the mortality of determine how many eggs were destroyed. Adults corn borer eggs was significantly affected by pred- were used only once. ator density (F = 74.53; df = 3, 16; P < 0.05) and One-way analysis of variance (ANOVA) fol- egg position (F = 531.44; df = 1, 16; P < 0.05) lowed by a Student-Newman-Keuls (SNK) test (Table 3). No significant differences (P > 0.05) (Sokal & Rohlf 1981) was used to analyze the effect occurred between egg mortality percentages for of different densities on total egg consumption corn borer eggs on the upper and lower parts of (percentage of eggs consumed of all those exposed). the leaves. Therefore, egg mortalities for upper and Two-way ANOV A (Sokal & Rohlf 1981) was used lower leaves were combined. to determine if predator density and egg position One-way ANOV A showed that there was no sig- had an effect on the mortality of corn earworm nificant difference in corn borer egg mortality on and corn borer eggs. One-way ANOV A (Sokal & the corn ear for the different predator densities. Rohlf 1981) was then used to analyze the effect of Corn borer egg mortalities on masses attached to different predator densities on the percentage egg the leaves were significantly different (SNK tests) mortality for corn borer and corn earworm eggs for all predator densities at the P = 0.05 level (Table on different parts of the corn plant. 3). As the predator density increased, the percent- age of egg mortality on the leaves increased. Table 3 also shows that eggs attached to the leaves dif- Results fered significantly in their mortality from that of The total percentages corn borer and corn ear- the eggs attached to the ears. The egg masses most worm eggs destroyed were significantly different frequently fed upon were those pinned on the (SNK tests) for all predator densities at the P = leaves. 0.05 level (Table 1 and 2). As the predator density Two-way ANOV A showed that the mortality of increased, the total percentage of eggs destroyed corn earworm eggs was significantly affected by increased. predator density (F = 338.20; df = 3,24; P < 0.05) and egg position (F = 649.72; df = 2,24; P < 0.05) (Table 4). One-way ANOV A showed that there was no significant difference in corn earworm egg mor- Table 2. Effect of O. insidiosus on total percentage of tality on the tassels for the different predator den- corn earworm eggs destroyed in 48 h sities. Corn earworm egg mortalities on masses pinned to the silks were significantly different (SNK Predator density Total % eggs destroyed, f ± SEMa tests) for all predator densities at the P = 0.05 level. o 12.44 ± 0.33a As the predator density increased, the percentage 1 18.44 ± 1.43b egg mortality on the silks increased. However, mor- 3 33.30 ± 2.32c tality of eggs attached to the leaves was shown to 6 54.44 ± 1.12d 12 74.00 ± 1.40e be significantly different only at the predator den- sity of 12 (Table 4).