Biological Control 66 (2013) 21–26 Contents lists available at SciVerse ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon Effect of fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) strain and diet on oviposition and development of the parasitoid Euplectrus platyhypenae (Hymenoptera: Eulophidae) ⇑ Mirian M. Hay-Roe , Robert L. Meagher, Rodney N. Nagoshi Behavior and Biocontrol Unit, USDA, ARS, CMAVE, 1700 SW 23rd Dr., Gainesville, FL 32608, United States highlights graphical abstract Euplectrus wasps preferred to oviposit on corn strain larvae fed corn plants. No oviposition preference was observed for corn or rice strain larvae fed grass. Larger parasitoid offspring resulted from the largest host fed corn plants. Wasp larval mortality occurred in hosts of both strains fed stargrass. article info abstract Article history: Oviposition tendency and subsequent development of the parasitoid wasp Euplectrus platyhypenae How- Received 24 August 2012 ard was compared using the corn and rice host strains of Spodoptera frugiperda (J. E. Smith) fed corn (Zea Accepted 3 March 2013 mays, ‘Truckers Favorite’) or stargrass (Cynodon nlemfuensis Vanderyst var. nlemfu ensis, ‘Florona’). In no- Available online 13 March 2013 choice and two-choice experiments using newly molted fourth instar hosts, female wasps preferred to oviposit on corn strain larvae fed corn plants. Rice strain larvae were parasitized when fed corn plants, Keywords: but only after the host had reached an optimal size. This preference might be due to differences in size Allelochemical between host strains at a given stage. No oviposition preference for corn or rice strain larvae fed grass Biological control was observ ed.When female wasps were given a choice between corn and rice strain larvae, they always Ectoparasitoid Fall armyworm produced more female offspring on the corn strain than the rice strain larvae, irrespective of the host Spodoptera frugiperda plant the larvae fed upon. Among rice strain hosts, those fed corn hosted more female offspring than Euplectrus platyhypenae those fed grass. The data also show that host quality had a direct effect on parasitoid size, since larger parasitoid offspring resulted from the largest host fed corn plants, and smaller offspring resulted from the smallest hosts, rice strain larvae fed stargrass. Furthermore, E. platyhypenae larval mortalit yoccurred in hosts of both strains fed stargrass, which may indicate that stargrass allelochemicals are not appropri- ate for this parasitoid. Implications of these results for biological control methods are discussed. Published by Elsevier Inc. 1. Introduction an important role in the evolution of caterpillar behavior (Fatouros et al. 2005; Poelman et al., 2011). It has been suggested that para- Parasitoid wasps have long been known to inflict substantial sitoid-caterpillar associations can be influenced by host plant fac- mortality on immature Lepidoptera and are therefore likely to have tors, including nutritional quality, phenology, and the presence of allelochemicals that, when ingested by the host, could inhibit par- ⇑ asitoid development and survival (Barbosa et al., 1991; Campbell Corresponding author. Fax: +1 352 374 5804. and Duffy, 1979; Reitz and Trumble, 1997). Also, in the last two E-mail address: mmhr@ufl.edu (M.M. Hay-Roe). 1049-9644/$ - see front matter Published by Elsevier Inc. http://dx.doi.org/10.1016/j.biocontrol.2013.03.003 22 M.M. Hay-Roe et al. / Biological Control 66 (2013) 21–26 decades many studies of these factors indicate it could be a signif- 2. Materials and methods icant contributor to the diversification of Lepidoptera with respect to host plant usage (Lill et al., 2002). 2.1. Insects Fall armyworm S. frugiperda is a potentially useful system for studies in this area. The species is highly polyphagous, with over E. platyhypenae was obtained from field populations of fall 60 different host plants identified to date (Casmuz et al., 2010; armyworm collected from corn at the Dairy Research Unit at the Pashley, 1988). This diverse host range is due in part to the University of Florida, Hague, Alachua Co., FL. In May 1008. Parasit- presence of two genetically distinct subpopulations, previously oids were reared in the laboratory at 24 °C, 65% humidity and at a identified as host strains (Pashley, 1988; Pashley et al., 1987). photoperiod of L:D 14:10, and were maintained in a The strains are morphologically indistinguishable, requiring the 27 Â 27 Â 27 cm Plexiglas cages. Cages had a screen on one side use of genetic markers to distinguish them (Lu and Adang, 1996; for ventilation and a 14 cm circular screen hole for access to the Nagoshi and Meagher, 2003; Nagoshi et al., 2006; Pashley, 1988; colony. Several smears of honey were placed on the roof of the Pashley et al., 1987). Their defining behavioral phenotype is host Plexiglas cage and a cotton ball saturated with water was placed preference, with the rice-strain preferentially found in turf and in a 1-oz acrylic Solo cup (Solo Cup Co., Urbana, IL) for parasitoid pasture habitats, while the corn-strain predominates in agricul- feeding. The colony was maintained in the laboratory for 9 months tural settings containing corn, sorghum, or cotton (Lu and Adang, before experiments were initiated. 1996; Nagoshi and Meagher, 2003; Nagoshi et al., 2007; Pashley, Fall armyworm rice strain larvae were collected from pasture 1988). This suggests that if these are populations undergoing incip- fields at the Range Cattle Research and Education Center, Ona, ient speciation, as previously hypothesized (Drès and Mallet, 2002; Hardee Co., FL, while the corn strain larvae were collected from Prowell, 1998), then there must be disruptive selection pressure corn fields at Hague. The two strains were identified by molecular for diverging host ranges. In addition, while there have been markers (Levy et al., 2002), as modified by Nagoshi and Meagher reports that the developmental performance and mortality of the (2003) and are currently maintained at the USDA, ARS, CMAVE strains can vary on different hosts, the results have been inconsis- Behavior and Biocontrol Unit in Gainesville, FL on an artificial pinto tent (often contradictory) and typically not of sufficient magnitude bean diet. Cohorts of these colonies were raised on ‘Trucker’s to easily explain the often strong compartmental distribution of Favorite’ corn and on ‘Florona’ stargrass in plastic Sterilite tubs the two strains into different habitats (Meagher et al., 2007; (Sterilite Corporation, Townsend, MA) [26 (d) Â 12.1 (h) cm] Pashley et al., 1995). More complicated selection pressures are containing metal screens (holes at 0.7 cm). Plant cuttings suggested. (15–17 cm long) were wrapped in wet paper towels to keep them The involvement of parasitoids in driving fall armyworm strain hydrated. When plant material was completely consumed, more divergence and asymmetrical distribution in the field is possible, material was added and the lower stems were placed on the top perhaps likely, given that high (>50%) levels of parasitism are not metal screen to be removed the following day. Previous research uncommon and the spectrum of available natural enemies is showed ‘Florona’ stargrass to be an excellent host for fall defined by habitat (Roland, 2000 ). In this scenario, a generalist armyworm (Meagher et al., 2007), although rearing parameters feeder becomes associated with specific plant hosts to escape can have a negative effect on larval mortality (Hay-Roe et al., natural enemies found in other habitats or to adapt plant 2011). The cohorts were maintained in environmental chambers allelochemicals as a defense mechanism. Support for this claim at 26 °C, 75% humidity and L:D 14:10 photoperiod. would be provided by the observations that the two strains exhibit different susceptibilities to parasitoid species in a manner influ- enced by diet. 2.2. E. platyhypenae oviposition preference To test this we examined a parasitoid wasp that is commonly associated with fall armyworm populations in Florida. Euplectrus Three experiments were performed to assess oviposition prefer- platyhypenae Howard (also in the literature as E. plathypenae; ences of E. platyhypenae females in response to corn and rice fall Hymenoptera: Eulophidae) is a gregarious ectoparasitic koinobiont armyworm host strains fed either corn or stargrass. The first study that attacks Lepidoptera larvae (Noctuidae, Pyralidae, Sphingidae examined the timing of oviposition in a choice test. A single newly and Tortricidae) (Luginbill, 1928; Murúa and Virla, 2004; Vickery, molted fourth-instar larva of each strain was placed on either corn 1929; Wilson, 1932). Before oviposition, females inject venom into or star grass in 25 Â 25 Â 25 cm Plexiglas containers, each with a the larvae to inhibit molting and arrest development (apolysis and 7 cm hole covered with 0.15 mm insect screen for aeration. ecdysis) without inducing host paralysis (Coudron and Puttler, Because fall armyworm larvae are morphologically similar, the 1988). Female wasps lay clusters of eggs on the dorsum of hosts, second proleg on the right was alternately clipped to facilitate host an area used by parasitoids to prevent defensive biting and egg strain differentiation (Hagler and Jackson, 2001). Three naïve, removal by the host. Parasitoid larval development is completed mated female wasps (females that were not previously exposed near the oviposition site, and pupation occurs along the ventral to larvae) were released in each cage (Bultman et al., 1997; side of the now moribund caterpillar, where they spin silky Coudron et al., 1997). The strain identity of the first larva detected cocoons. E. platyhypenae has been proposed as a good candidate with an egg cluster was recorded. Oviposition generally occurred in for use as a biological control agent for the fall armyworm the first 24 h period. Eighty larvae fed corn plants (40 larvae from (Molina-Ochoa et al., 2001 ), but few studies have been carried each strain) and 80 larvae fed stargrass (40 larvae from each strain) out to determine optimal ecological conditions.