Podisus maculiventris (Say) is a generalist predator of over one hundred species of insects, including approximately fifty different crop pests. Its primary prey items are larval Coleoptera and Lepidoptera (Warren & Wallis 1971; McPherson 1980; Wiedenmann et al. 1994), and it can have a significant impact on pest populations in these orders (DeClerq et al. 1998). In greenhouse studies, DeClerq et al. (1998) report a reduction of tomato looper Chrysodeixis chalcites (Esper) populations of 40% in 48 h and a 65% decrease in leaf-feeding damage after 1 week when fourth instar P. maculiventris were released at a predator:prey ratio of 1:3.3. Adults and nymphs of P. maculiventris can be found in a variety of agroecosystems such as soybean, alfalfa, corn, potato, apple, grape, and brassica, and in other plants and plant communities such as goldenrod, shrubland, deciduous forest, hemlock, and pine (Culliney 1986; Wieden-mann et al. 1994). Adults overwinter under ground debris or under the bark of trees. Podisus maculiventris occurs from Quebec to British Columbia and south to Florida and Arizona (McPherson 1982). However, the occurrence and activity of this species may vary throughout its distribution.
The objective of this study was to determine the temporal occurrence of P. maculiventris at a site in northern Florida. This type of information can be valuable when assessing the potential predator guild of an insect pest throughout the growing season of a crop in a specific area. Moreover, understanding the occurrence of a predator species can be useful when integrating pest management tactics in agricultural systems.
The study took place at the Florida Agricultural and Mechanical University, Viticulture and Small Fruit Research Center, Tallahassee, Florida. The site is located in north Florida at a latitude of approximately 30°28′70′′N and longitude of 84°10′31′′W, 62 m above sea level. From west to east the site consisted of grape Vitis rotundifolia Michx, mowed grass, golden rod Solidago L. spp., small trees and shrubs, and large trees.
Six mesh screen funnel traps contained within a plastic container (19.5 cm in height, with a 14-cm diameter funnel ending in a 4-cm diameter entrance hole 8 cm deep, and a removable sealed bottom) (Fig. 1) were hung on small trees between the grape vineyard and large trees. The traps were 45 m apart and placed 1-1.5 m above ground level. Traps were baited every two weeks with a synthetic male sex pheromone formulation of 3478 μl (E)-2-hexenal, 193.6 μl benzyl alcohol, and 4246 l (±)-α-terpineol (Aldrich et al. 1984; Aldrich 1988). This pheromone blend attracts males and females of P. maculiventris (Aldrich et al. 1984; Aldrich 1988). Baiting the traps every two weeks allowed the majority of the pheromone to evaporate and allowed some pheromone to remain in the trap to maintain its attractiveness. Each trap contained a 10-ml glass vial with a cotton wick and approximately 7 ml of pheromone. For each season, traps were set or inspected at approximately 11:00 AM EDT. In 2001, 2002, and 2003 traps were set on 7 June 2001, 1 March 2002, and 28 February 2003. Sampling began three days after trap placement. Traps were inspected twice a week from 10 June 2001-26 October 2001, 4 March 2002-17 June 2002, and 3 March 2003-16 June 2003. Data are plotted with moving average trend lines for visual interpretation (Fig. 2).
In the 2001 season, adults of P. maculiventris were captured within the first three days after trap placement, indicating that adults were already active. Adults were most abundant in June and peaked on 22 June 2001 (Fig. 2A). Captures remained low (<2.0 ± 0.3 adults/trap) from 4 July 2001-26 October 2001 (Fig. 2A). In the 2002 and 2003 seasons, sampling began in early March, before P. maculiventris were active. During both seasons, overwintering adult P. maculiventris became active in March, with populations peaking in May. Adult populations peaked on 13 May 2002 and 23 May 2003. Populations decreased in late-May during the 2002 and 2003 seasons and increased, to a lesser extent, in mid-June (Figs. 2B and 2C). Large decreases in adult captures in May likely indicate the end of the first generation offspring from the progeny of overwintering adults. The presence of all life stages explains the delay in adult populations during the second generation. Reduced activity in adult populations during the summer months also could be caused from decreased survival of various developmental stages at higher temperatures (DeClercq & Degheele 1992). Adult activity from March through September and peaks of adult activity in May and June are similar to results found by Aldrich et al. (1984) at a site in Geneva, NY.
The overall sex ratio of adults captured was 1:2 males:females (n = 297). Using a similar pheromone formulation, Aldrich (1988) reports a ratio of approximately 2:1 males:females. This difference could be due to differences in trap type, frequency of rebaiting the traps, location, and/or pheromone blend (Aldrich et al. 1984; Aldrich 1988). Overwintering adult captures from the first trap catch in 2002 through 29 April 2002 revealed a male:female of 1:1. Similarly, overwintering adult captures from the first trap catch in 2003 through 28 April 2003 revealed a male:female of 1:1. Adult tachinids, most likely the endoparasitoid Hemyda aurata Robineau-Desvoidy, were only captured on three occasions.
We thank Ryan Stype, Ricardo Smith, and Byron Franklin, Jr. for assistance. We also thank Stephen Hight, USDA-ARS and Kenneth Bloem, USDA-APHIS for helpful reviews of this manuscript. This research was supported in part by the USDA-Sustainable Agricultural, Research and Education grant RD309-040/3581407 and by cooperative agreement 58-6615-8-022 UDSA-ARS and Florida A&M University.
In northern Florida, P. maculiventris emerge in March-April and begin overwintering in October-November. The data indicate that P. maculiventris has a bimodal phenology, with peak abundance in May and a second less prominent peak in June. Comparisons of trap collections in northern Florida and central New York suggest little deviation in adult seasonal activity of P. maculiventris between the northeastern and southeastern USA.