PLANT- INTERACTIONS Examination of the Pest Status of Corn-Infesting (Diptera)

GAURAV GOYAL,1 GREGG S. NUESSLY,1 DAKSHINA R. SEAL,2 GARY J. STECK,3 4 5 JOHN L. CAPINERA, AND ROBERT L. MEAGHER

Environ. Entomol. 41(5): 1131Ð1138 (2012); DOI: http://dx.doi.org/10.1603/EN11265 ABSTRACT Larvae of 11 species of picture-winged ßies (Diptera: Ulididae) are known to feed on corn plants (Zea mays L.) in the western hemisphere. Larvae emerge from eggs deposited in leaf axils and corn silk to feed mostly within ears, but the primary versus secondary nature (i.e., pest status) of their infestation is not known for all of these species. Choice and no-choice tests by using a split-plot design were conducted in greenhouse and Þeld trials to determine the pest status on sweet corn of three of these species found in Florida: Chaetopsis massyla (Walker), eluta Loew, and E. stigmatias Loew. The main treatments (uninfested ears and ears experimentally infested with either Spodoptera frugiperda [Lepidoptera: Noctuidae] or E. eluta larvae) were applied at Þrst silk. The subtreatments (C. massyla, E. eluta, or E. stigmatias adults caged on ears) were applied 7 d later and maintained for 10 d. All three ßy species were reared from uninfested and experimentally infested ears in both choice and no-choice tests in greenhouse and Þeld trials conÞrming both primary and secondary modes of ear infestation. More ßies of all three species emerged from ears that were preinfested with S. frugiperda compared with uninfested ears suggesting either preference for or greater survival within ears previously infested by S. frugiperda. Fewer E. eluta and E. stigmatias emerged from ears preinfested with E. eluta in no-choice Þeld tests, suggesting that previous infestation by this ßy may negatively affect oviposition or that older ßy larvae affect survival of neonate larvae. All three species studied here should be considered primary pests that can render unprotected sweet corn ears unmarketable.

KEY WORDS Spodoptera frugiperda, fall armyworm, , sweet corn

Sweet corn is an important vegetable crop for Florida; Barbosa et al. 1986, Wyckhuys and OÕNeil 2007, Goyal leading the nation in area harvested (17,037 ha) and et al. 2010). The larvae feed on tassels in the whorl worth an estimated US$189.2 million in 2010 (Anon- and on silk, kernels, and cobs disrupting pollination and ymous 2011). In addition to recognized Noctuidae greatly reducing marketability through damage and (Lepidoptera) whorl and ear pests such as fall army- infestation of the ears (App 1938, Bailey 1940, Seal worm [Spodoptera frugiperda (J. E. Smith)] and corn and Jansson 1989, Hentz and Nuessly 2004). Van earworm (Helicoverpa zea [Boddie]), nine picture- Zwaluwenburg (1917) Þrst reported E. stigmatias as a winged ßy (Diptera: Ulidiidae) species [Chaetopsis corn pest in Puerto Rico where it damaged up to 100% massyla (Walker)], Eumecosomyia nubila (Wiede- of untreated corn. This ßy Þrst was discovered dam- mann), Euxesta annonae (F.), E. eluta Loew, E. major aging corn in Miami, FL in 1938 (Barber 1939) and by Wulp, E. nitidiventris Loew, E. sororcula Wiedemann, mid century had moved north into central Florida E. stigmatias Loew, and E. thomae Loew] have been (Hayslip 1951). This species has become a serious pest found in corn (Zea mays L.) in North America (in- of Florida sweet corn requiring multiple insecticide cluding central America from Mexico to Panama and applications during the ear stage to maintain a mar- Caribbean countries) (Chittenden 1911, Painter 1955, ketable crop (Mossler 2008). Despite the damage inßicted by these ßies, system- atic, biological, and ecological studies of ulidiid pests 1 Corresponding author: G. S. Nuessly, Everglades Research and Education Center, University of Florida, Institute of Food and Agri- of sweet corn in Florida has been complicated by cultural Sciences, 3200 E. Palm Beach Rd., Belle Glade, FL 33430, incomplete systematic references, early incorrect Phone: 561-993-1559 (e-mail: gnuessly@uß.edu). identiÞcations, and long periods during which these 2 Tropical Research and Education Center, UF, IFAS, 18905 S.W. pests were not active in the major sweet corn growing 280 St., Homestead, FL 33031. 3 Division of Plant Industry, Florida Department of Agriculture and areas of the state. IdentiÞcation to species for speci- Consumer Services, P.O. Box 147100, Gainesville, FL 32614. mens of United States origin largely relies on keys of 4 Department of Entomology and Nematology, UF, IFAS, P.O. Box foreign species (Steyskal 1968) or unpublished keys 110620, Gainesville, FL 32611. by the same author. A photograph on the front cover 5 United States Department of Agriculture, Agricultural Research Service, Insect Behavior and Biocontrol Research Unit, 1600 S.W. 23rd of a Florida Agricultural Experiment Station Circular Drive, Gainesville, FL 32608. (Hayslip 1951) was incorrectly identiÞed as E. stig-

0046-225X/12/1131Ð1138$04.00/0 ᭧ 2012 Entomological Society of America 1132 ENVIRONMENTAL ENTOMOLOGY Vol. 41, no. 5 matias and only recently recognized as E. eluta by a were designed to represent the state of ear infestation distinctive wing character visible in the image. Euxesta at the time of exposure to the subtreatments. Main stigmatias appears to have been a continuous pest in treatments consisted of uninfested ears and ears in- sweet corn in extreme southern Florida (Miami-Dade fested with either E. eluta or S. frugiperda larvae. Five County). However, based on interviews of current second-instar E. eluta larvae from a laboratory colony and retired growers by the authors, Palm Beach maintained at EREC (see details below), or three County growers did not experience problems with third-instar S. frugiperda larvae (corn strain) from a these ßies from the late 1950s until early 1991 when it laboratory colony maintained on artiÞcial diet at the reemerged as a pest in eastern Palm Beach County. USDA-ARS Insect Behavior and Biocontrol Research Infestations of E. stigmatias in sweet corn had again Unit, Gainesville, FL, were placed within the silk spread northward into the corn-growing region south channel of an ear with the aid of a Þne camelÕs-hair of Orlando by 1993. brush (size 0). Preliminary tests determined that these In corn surveys conducted between 2006 and 2008, levels of infestation were the lowest to provide con- four ulidiid species were reared from sweet and Þeld sistent levels of injury to corn ears. Second-instar E. corn in Florida (Goyal et al. 2011a). Two species were eluta larvae were recognized easily by the nonover- found throughout the state on Þeld and sweet corn (C. lapping ranges of body length and width (Goyal et al. massyla and E. eluta), whereas two were found only in 2011b). Third-instar S. frugiperda larvae were recog- corn grown in the southern half of the Florida pen- nized based on their body length, color, and exuvia insula (E. annonae and E. stigmatias). Although four (Luginbill 1928). All ears were covered with pollina- species were collected from Florida commercial sweet tion bags (6.25 by 2.5 by 21.25 cm, held tightly around corn Þelds, it was not initially known which of the the middle of the ears with rubber bands) between species were primary pests that required pest man- application of the main and subtreatments to avoid agement strategies to produce a proÞtable crop. Goyal unintended insect infestation. et al. (2010) determined that C. massyla was a primary The subtreatments were male:female pairs of C. pest of both Þeld and sweet corn in Florida, but E. massyla, E. eluta, and E. stigmatias. Subtreatments annonae and E. eluta have not been formally studied to were initiated 7 d after application of the main treat- determine their pest status in North America. ments. In the no-choice tests, the subtreatments con- Knowledge on the pest status of corn-infesting in- sisted of caging one ßy species on three ears (see sects is important for the continued development of below), each with a different main treatment. There- integrated pest management strategies for corn as new fore, each ßy species did not have a choice among the pests emerge. Although control strategies are required three main treatment effects. Each of the three ßy to prevent primary pests from entering ears, no treat- species was introduced to a different subgroup of ment is required for pests with a secondary mode of three ears. One no-choice test was conducted in a attack as the presence of prior infestation is required for their feeding. Ulidiid eggs frequently have been greenhouse and another was conducted in the Þeld. observed within the entry and exit holes of Lepidop- Choice tests were conducted in the Þeld by using tera larvae on corn ears (G.G., personal observations). groups of three adjacent plants (one with each main Scully et al. (2000) reported E. stigmatias and treatment) enclosed by small cages (see below). Sub- Spodoptera frugiperda larvae (J. E. Smith) (Lepidop- treatments in the choice tests were applied by releas- tera: Noctuidae) infesting ears concurrently in south- ing single species of ßies into a cage so that the adults ern Florida. Information on the relative attractiveness were free to choose to oviposit among the ears with of infested versus uninfested ears may be useful for the three main treatments. The subtreatments for future research on the relative importance of food choice and no-choice tests were removed 10 d after resources and on potential oviposition cues for these initiation of the subtreatments. Ear cages were re- ßies. Therefore, the objective of this study was to moved along with adults from the no-choice tests and measure and compare the pest status and relative adults were removed from caged plants in the choice importance of prior infestation of corn ears by the tests. The corn ears were re-covered with pollination three most common ulidiid species found infesting bags as discussed above In Experimental Design to sweet corn in Florida: E. eluta, E. stigmatias, and C. protect the ears from additional infestation until the massyla. end of the test. Late last-instar Ulidiidae larvae normally leave corn ears to pupate within the soil litter or in the dried silks Materials and Methods at the ends of ears (App 1938). pupae Choice and no-choice tests were conducted to that developed from the main treatment were re- measure the pest status of the ßies. The studies were moved carefully from ears 3 d after application of the conducted in a greenhouse and in Þelds at the Ev- subtreatment to avoid any confusion with immatures erglades Research and Education Center (EREC), developing from the subtreatment in which E. eluta Belle Glade, FL (latitude: 26.666384, longitude: adults were caged on ears. Spodoptera frugiperda lar- Ϫ80.633312). vae take longer to develop to the pupal stage than the Experimental Design. All experiments were ar- ßy larvae and removing them from the ears would ranged as a split-plot design with three main treat- have destroyed the microhabitat at the end of the ears ments and three subtreatments. The main treatments where the majority of ulidiid larvae develop. There- October 2012 GOYAL ET AL.: PEST STATUS OF PICTURE-WINGED INFESTING CORN 1133 fore, the lepidopteran larvae were allowed to com- eclosion. The preoviposition period for the three spe- plete development within the ears. cies was 10, 3, and8dforC. massyla, E. eluta, and E. The tests were terminated 17 d after initiation of the stigmatias, respectively. Therefore, to attempt to com- subtreatments when the top third of each ear was pensate for expected low oviposition potential of these incised using a knife and placed individually in 1.83- older, Þeld-collected ßies, Þve male:female pairs of liter Ziploc (S.C. Johnson & Son, Inc., Racine, WI) ßies were used in the greenhouse no-choice tests. bags. The ears were held in the same conditions as They were caged on each ear by using 11 by 30 cm, used for colony maintenance (see below). To reduce 17-mesh bags (17 openings per linear 2.5 cm). A cotton the accumulation of excess moisture and the growth of ball dipped in 50Ð60% honey solution was placed in fungi, two paper towels were added to each bag and each bag as food for the adults. The open end of each changed every 48 h. The bags were left partially open bag was held tightly around the ear with a binder clip to facilitate aeration by using box fans. Pupae were to prevent ßies escaping. The mesh size of the bags was removed daily from the bags and placed on moistened small enough to cage the ßies, but large enough to Þlter paper (Whatman 3, Whatman International Ltd, allow natural pollination of the ears. The subtreat- Maidstone, England) in covered petri dishes for adult ments were maintained for 10 d on the ears during emergence. The dishes were sealed with ParaÞlm which time dead adults were replaced at 48-h inter- (Pechiney Plastic Packaging, Chicago, IL) to reduce vals. Eight replicates of the split-plot trials (72 plants moisture loss. Adult emergence in the petri dishes was total, 24 plants for each subtreatment) were con- recorded every 72 h. ducted at the same time in the greenhouse. No-Choice Greenhouse Tests. Studies Þrst were No-Choice Field Tests. No-choice Þeld studies were conducted using potted plants in a greenhouse in conducted during May 2008 at the EREC. Sweet corn December 2007 to evaluate the methods for no-choice (Obsession) was planted 17.8 cm apart on 76.2-cm and choice Þeld tests planned for the following years. row-centers on 19 March 2008 in Dania muck soil Sweet corn (ÔObsessionÕ, Seminis Vegetable Seeds, using a planter unit pulled with a tractor. Liquid starter Inc., Saint Louis, MO) was planted on 17 October fertilizer (11Ð34 Ϫ0, N-P-K) was applied in the seed 2007, in 18.9-liter (5-gal) buckets Þlled with Dania furrow at planting after which supplemental fertilizer Muck soil collected at the EREC. Fertilizer based on applications were managed according to local stan- the plant requirements (14Ð14-14 [N-P-K], 15 g per dards (Ozores-Hampton et al. 2012). Insecticides bucket) was hand-mixed with the soil in buckets one were used to protect the plants from lepidopteran day before planting. Three seeds initially were planted larvae until tassel emergence after which no insecti- in each bucket and then thinned to one seed per cides were applied. The same procedures for applying bucket on 5 November. Plants were irrigated as and evaluating main and sub-treatments in the green- needed. The insecticide Proaxis (gamma-cyhalothrin, house no-choice trial were used in the Þeld no-choice Dow Agro Sciences, Indianapolis, IN) was used to trial with the following two exceptions. Flies from protect the plants from Lepidoptera larvae until tassel laboratory colonies (see below) rather than Þeld-col- emergence after which no insecticide was applied. lected ßies were used in the trial. Only one pair of 5Ð15 The plants were grown in a fan- and pad-cooled green- d-old adults was caged on each ear as subtreatments house maintained within 3.5ЊC of the ambient tem- instead of Þve pairs as used in the greenhouse trial. perature. In total, 100 plants were grown in buckets Preliminary tests with individual lab-reared ßies con- and 72 were used for the experiment. Þrmed that females in this age bracket could deposit The corn plants were moved at tassel push into a greater number of eggs than the 5-pairs of ßies groups of nine plants, each with three subgroups of produced earlier in the greenhouse no-choice tests three plants, in preparation for infestation. One of based on the number of larvae that emerged from ears. each of the main treatments (uninfested ear, or ex- Three adjacent plants with one ear each were used for perimentally infested with E. eluta or S. frugiperda each three-plant sub-group. Nine replicates of the larvae) was applied to an ear on one plant in each split-plot trials (81 plants total, 27 for each subtreat- subgroup. Field-collected ßies of all three species ment) were conducted at the same time in the Þeld. were used for the subtreatments in the greenhouse Choice tests. These trials were conducted in the no-choice test, because laboratory colonies (see be- Þeld during December 2009 and May 2010. Sweet corn low) were not fully established for E. stigmatias and C. was planted on 15 and 29 September 2009 (ÔGarrisonÕ, massyla when it was time to initiate the trial. Flies were Rogers Brand, Syngenta Seed, Wilmington, DE), 15 collected from corn Þelds at the EREC by using sweep February, and 3 March 2010 (Obsession) by using the nets over a 6-d period to obtain enough of each species same planting arrangement and equipment on the for the trial. The ßies were held under laboratory same soil type at EREC as for the no-choice Þeld test. conditions (see below) so that only apparently Tests were initiated with the observance of Þrst silk healthy and undamaged ßies could be used for the emergence from ear tips. Choice tests were conducted tests. The ßies had been held 8Ð14 d by the time they within cages (20-mesh, 2.0 m tall by 0.9 m by 0.9 m) were used in the trial. Concurrent studies by Goyal supported internally by polyvinyl chloride pipes (2010) found oviposition rates for these ßies vary from placed over three adjacent plants within the same 1 to 23 eggs per day on artiÞcial diet within 5Ð15 d of plant row. The ends of the pipes were buried 0.4 m adult eclosion. The greatest oviposition for all three beneath the soil and ropes were placed over the tops species was observed on the eleventh day after adult of the cages and staked to the ground to anchor the 1134 ENVIRONMENTAL ENTOMOLOGY Vol. 41, no. 5 cages in inclement weather. Cages were equipped maintained at 26.5 Ϯ 1.0ЊC, 55Ð70% RH, and a photo- with a full-length zipper to provide easy access to the period of 14:10 (L:D) h. Flies used in the experiment plants. Three adjacent plants were selected and caged had completed three to six generations before begin- based on the absence of previous insect or mechanical ning the studies. damage to ears. The tips of ears initially were covered Statistical Analysis. Analysis of variance of the re- with pollination bags held with rubber bands to pro- sults of the choice and no-choice tests was conducted tect the ears until the main treatments were applied. using Proc GLM (SAS Institute 2008) because of the The three main treatments (i.e., uninfested, experi- unbalanced design of the experiments (i.e., unequal mentally infested with E. eluta or S. frugiperda) were numbers of ears exposed per species). The results of applied to these ears as above in the no-choice tests the no-choice tests were conducted separately for the and then recovered with the pollination bags within greenhouse versus the Þeld tests because of differ- 24 h of caging the groups of three plants. Subtreat- ences in the environment and the number of ßy pairs ments were applied by releasing Þve pairs of 5Ð15-d- caged on the ears between the two tests. The main old laboratory-reared ßies of a single species in each treatments (ears uninfested, or infested with either E. cage 7 d after application of the main treatments. The eluta or S. frugiperda), subtreatments (ßy species), pollination bags were removed from ears before re- and their interactions were modeled as the indepen- leasing the ßies into the cages. The larger search area dent variables in the no-choice test analyses. The num- afforded the ßies in the Þeld cages compared with the ber of adults that emerged per corn ear was modeled individual ear cages used in the no-choice tests sup- as a dependent variable in the no-choice test analyses. ported the decision to use Þve pairs of lab-reared ßies For the choice test analyses, experiment date and its in the choice tests rather than the single pair used in interaction with the other independent variables were the no-choice Þeld tests. No attempt was made to added to the list of modeled independent variables. sample and replace ßies that may have died in the Recent studies on the biology of these ßies indicated cages to reduce the chances of introducing competing that all three species have different reproductive po- ulidiid species or predators into the cages. Two cotton tentials in terms of the number of eggs deposited balls dipped in a 50Ð60% honey solution were placed during their reproductive periods (Goyal 2010). in each cage as a food source for the ßies. Ears within Therefore, the percentages of adults that emerged per the cages were re-covered with pollination bags 10 d cage from each ear were modeled as a dependent after exposing them to the subtreatments. The bags variable in the choice test analyses. The percentage of were removed after 7 d and ears harvested and held for adults that emerged per main effect ear treatment was adult emergence as above for the no-choice tests. calculated by dividing the number of adults emerged The choice Þeld tests were repeated four times per ear by the number emerged per cage. The per- between December 2009 and June 2010. Six replica- centages of emerged adults were transformed before tions of the split-plot trial (18 cages, 54 plants total, 18 analyses by using arcsine-square root to improve the plants for each subtreatment) were started in each of normality and homogeneity of variance. Untrans- the Þrst and second weeks of December. Two addi- formed data were used for presentation purposes. tional choice Þeld tests also were started in May 2010, Least square means were used rather than arithmetic but an unequal number of subtreatment replications means because of signiÞcant interaction among the were established in these later trials to take advantage independent variables. The TukeyÕs HSD test (SAS of all the available cages. Therefore, seven replications Institute 2008) was used for posthoc means separation each with C. massyla and E. eluta, and six replications with P Յ 0.05. with E. stigmatias were started (20 cages, 60 plants total, 21 for each of the C. massyla and E. eluta sub- Results treatments and 18 for the E. stigmatias subtreatments) in each of the Þrst and second weeks of May. No-Choice Tests. All three ulidiid species oviposited Colony Maintenance. Colonies of C. massyla, E. and were able to complete development from egg to eluta, and E. stigmatias were initiated from adults col- the adult stage in uninfested ears, as well as in ears lected using sweep nets in corn Þelds in and around already infested with S. frugiperda or E. eluta larvae. In Belle Glade, FL. The ßies were brought to the labo- the 2007 greenhouse trial, ear infestation (F ϭ 2.64; ratory where they were provided with Helicopverpa df ϭ 2, 63; P ϭ 0.0794) and ßy species (F ϭ 15.86; df ϭ zea Boddie (Lepidoptera: Noctuidae) artiÞcial diet 2, 63; P Ͻ 0.0001), but not the ear infestation ϫ ßy (product F9393B, Bio-Serv, Frenchtown, NJ) as an species interaction (F ϭ 0.85; df ϭ 4, 63; P ϭ 0.5010), oviposition medium and larval food by using the affected the number of adults that emerged from ears. method of Hentz and Nuessly (2004). Mature larvae More E. stigmatias than E. eluta adults emerged from leaving the diet pupated in cotton balls used to plug uninfested ears and ears already infested with S. fru- the end of diet tubes or in cotton sheets used to line giperda or E. eluta larvae (Table 1). More E. stigmatias trays where diet tubes containing developing larvae than C. massyla adults emerged from S. frugiperda- were maintained after removal from oviposition cages. infested ears. The cotton balls and sheets were placed within the In the 2008 no-choice Þeld study, ear infestation adult oviposition cages to allow the adults to emerge (F ϭ 27.22; df ϭ 2, 72; P Ͻ 0.0001), ßy species (F ϭ from pupae directly into the colony. All stages of all 11.34; df ϭ 2, 72; P Ͻ 0.0001), and the infestation ϫ ßy three species were maintained in an insectary room species interaction (F ϭ 2.93; df ϭ 4, 72; P Ͻ 0.0266) October 2012 GOYAL ET AL.: PEST STATUS OF PICTURE-WINGED FLIES INFESTING CORN 1135

Table 1. Least square mean ؎ SEM (range) number of adults that emerged per corn ear in no-choice tests conducted in a greenhouse in 2007

Main effects treatment Subtreatment ßy speciesa E. eluta S. frugiperda Uninfested C. massyla 10.6 Ϯ 2.5cd (2Ð20) 11.0 Ϯ 2.5cd (0Ð22) 14.0 Ϯ 2.5bcd (6Ð40) E. eluta 8.0 Ϯ 2.5d (0Ð19) 13.0 Ϯ 2.5cd (0Ð24) 10.1 Ϯ 2.5cd (4Ð18) E. stigmatias 16.9 Ϯ 2.5bc (6Ð24) 25.4 Ϯ 2.5a (13Ð38) 21.1 Ϯ 2.5ab (12Ð29)

Mean Ϯ SEM followed by different letters are signiÞcantly different (TukeyÕs HSD, P Ͻ 0.05, SAS Institute 2008). a n ϭ 8 per ßy species per main effects treatment. signiÞcantly affected the number of adults that Discussion emerged from ears. SigniÞcantly more adults of all the All three ßy species were reared from uninfested three species emerged from ears already infested with corn ears in both choice and no-choice tests, indicat- S. frugiperda than with E. eluta (Table 2). More E. ing that these ßies attack corn as primary pests. This stigmatias and C. massyla adults emerged from S. fru- is the Þrst known report of E. eluta as a primary pest giperda-infested than uninfested ears. The number of of sweet corn in North America. All three species also E. eluta and E. stigmatias that emerged from unin- oviposited and completed development in ears al- fested ears were greater than from E. eluta-infested ready infested with S. frugiperda or E. eluta larvae, ears. More E. stigmatias and E. eluta than C. massyla indicating that they can successfully use previously adults emerged from uninfested ears. Greater num- damaged ears as hosts. The current results were in bers of E. stigmatias than the other two ßy species accordance with some of the previous studies done on emerged from S. frugiperda-infested ears. The mean the primary and secondary nature of these ßies. Chae- number of adults of all three species that emerged per topsis massyla were reared from uninfested standard ϫ ϫ ear was 1.5 to nearly 2.4 greater in ears already sweet corn and Bacillus thuringiensis-enhanced sweet infested with S. frugiperda than with E. eluta. corn in commercial and experimental Þelds in south- Choice Tests. All three ßy species deposited eggs ern Florida (Goyal et al. 2010). The secondary mode and completed development to the adult stage in un- of attack of C. massyla has been reported on wetland infested ears and in those already infested by S. fru- monocots such as cattail, Typha latifolia L. (Typhac- giperda or E. eluta. The percentage of adults that eae: Typhales) previously damaged by moth larvae emerged per ear was signiÞcantly affected by ear in- (Lepidoptera: Noctuidae), and stems of Carex la- festation (F ϭ 63.67; df ϭ 2, 216; P ϭϽ0.0001) and ear custris Willd. (Cyperaceae: Cyperales) previously infestation ϫ ßy species interaction (F ϭ 6.53; df ϭ 4, damaged by larvae of Epichlorops exilis (Coquillett) 216; P ϭϽ0.0001), but not by ßy species (F ϭ 0.13; df ϭ (Diptera: Chloropidae) (Allen and Foote 1992). Eu- 2, 216; P ϭ 0.8749) or replicate (F ϭ 63.67; df ϭ 3, 216; xesta eluta was identiÞed as a primary pest of corn by P ϭ 0.9807). Data from the four replicates were pooled Arce de Hamity (1986) in Jujuy, Argentina. Both Arce for mean comparison of adults that emerged per ear, de Hamity (1986) and Frõ´as (1981) in Chile reported because replicates were not a signiÞcant source of that E. eluta completed development in ears damaged variation in the model. SigniÞcantly greater percent- by other . has been recog- ages of adults of all three ßy species emerged (i.e., nized as a primary pest of sweet corn for over 90 yr subtreatments) from ears preinfested (i.e., main treat- (Van Zwaluwenburg 1917) and has been reported as ments) with S. frugiperda compared with those with E. a secondary pest of several fruits (Seal et al. 1996). eluta (Table 3). Greater percentages of C. massyla and The colonization of sweet corn by these ßies likely E. eluta emerged from S. frugiperda-infested ears than began as an extension of feeding habits that evolved uninfested ears. A greater percentage of E. eluta than along with the development of maize as a crop in E. stigmatias emerged from S. frugiperda-infested ears, Central America. Picture-winged ßies have been rec- whereas a greater percentage of E. stigmatias than E. ognized as pests of Þeld corn in Central America for eluta emerged from uninfested ears. many years (Painter 1955). Field surveys in 2008 and

Table 2. Least square mean ؎ SEM (range) number of adults that emerged per corn ear in no choice tests conducted in the field in 2008

Main effects treatment Subtreatment ßy speciesa E. eluta S. frugiperda Uninfested C. massyla 15.1 Ϯ 2.6d (10Ð23) 25.2 Ϯ 2.6bc (8Ð42) 17.4 Ϯ 2.6d (4Ð20) E. eluta 17.0 Ϯ 2.6d (4Ð26) 29.1 Ϯ 2.6b (19Ð42) 25.4 Ϯ 2.6bc (8Ð36) E. stigmatias 18.2 Ϯ 2.6cd (10Ð29) 43.3 Ϯ 2.6a (21Ð58) 26.9 Ϯ 2.6b (20Ð35)

Mean Ϯ SEM followed by different letters are signiÞcantly different (TukeyÕs HSD, P Ͻ 0.05, SAS Institute 2008). a n ϭ 9 per ßy species per main effects treatment. 1136 ENVIRONMENTAL ENTOMOLOGY Vol. 41, no. 5

Table 3. Least square mean ؎ SEM (range) percentage adults that emerged from corn ears in choice tests

Main effects treatments Subtreatment ßy speciesa E. eluta S. frugiperda Uninfested C. massyla 17.5 Ϯ 3.6de (0Ð52.2) 57.8 Ϯ 3.6ab (0Ð100) 24.7 Ϯ 3.6cde (0Ð87.5) E. eluta 16.9 Ϯ 3.6de (0Ð100) 68.1 Ϯ 3.6a (0Ð97.7) 14.9 Ϯ 3.6e (0Ð43.8) E. stigmatias 22.0 Ϯ 3.8de (0Ð40) 43.2 Ϯ 3.8bc (0Ð100) 34.7 Ϯ 3.8cd (0Ð100)

Mean Ϯ SEM followed by different letters are signiÞcantly different (TukeyÕs HSD, P Ͻ 0.05, SAS Institute 2008). a n ϭ 24 ears for E. stigmatias and 26 for E. eluta and C. massyla per treatment.

2009 conÞrmed that three species of Ulididae also eggs on cabbage plants previously damaged by locusts attacked Þeld corn during the R1 and R2 stages in than on undamaged plants. However, signiÞcantly Florida (Goyal et al. 2011a). Sweet corn is historically fewer E. eluta and E. stigmatias adults emerged from very new on the time scale of maize development. ears that were already infested with E. eluta larvae Beyond the sweetness and softer pericarp traits bread compared with uninfested ears in the 2008 no-choice into sweet corn, additional traits for easier hand shuck- Þeld tests. It is possible that females of these ßies were ing have resulted in more open silk canals and looser deterred from depositing eggs in ears infested with ßy husks. These traits likely allow easier access by ulidiid larvae. Prokopy (1975) determined that female Rhago- larvae into ears and results in greater numbers of letis fausta (Osten Sacken) (Diptera: Tephritidae) larvae in the milk- and soft-dough stage kernels of deposited a pheromone on sour cherries (Prunus cera- sweet than Þeld corn (Scully et al. 2000). Feeding sus L. [Rosales: Rosaceae]) that deterred repeated tunnels produced by S. frugiperda larvae through the oviposition attempts by the same species. Alterna- silk channel may further ease the access of ulidiid tively, older larvae already infesting the ears (main larvae to the cob and kernels compared with ears treatment) may have negatively affected the devel- without substantial silk channel damage (Nuessly et al. opment or survival of the neonate larvae that emerged 2007). from eggs (subtreatment). In several experiments The results of greater numbers and percentages of conducted by Crombie (1944) on inter- and intras- ßies emerging from S. frugiperda-infested than unin- peciÞc competition with two grain-infesting species, fested ears in both choice and no-choice trials indi- Sitotroga cerealella (Olivier) (Lepidoptera: Gelechii- cates that oviposition by these three ßy species was not dae) and Rhizopertha dominica (Fabricius) (Co- deterred by prior infestation. Several genera of Uli- leoptera: Bostrichidae), survival was greatest for diidae are saprophagous with some phytophagous in whichever species or larvae of the same species in- nature (Hawley 1922, Chittenden 1927, Merrill 1951, fested the grain Þrst. Chemical or physical changes in Allen and Foote 1967, Kameneva and Korneyev 2010). plants because of herbivory, as well as competition for It is possible that C. massyla, E. eluta, and E. stigmatias the same resource, may be affecting outcome of these evolved their feeding habits from saprophagous to interactions among the four species tested in the cur- phytophagous as more accessible plant foods became rent study. available. Allen and Foote (1967) found that Chae- Differences in the experimental designs of the 2007 topsis spp. larvae fed on healthy tissue surrounding the and 2008 no-choice tests may have resulted in more entry wounds in plant stems created by Lepidoptera ßies emerging from ears in the second than Þrst trial. larvae. These ßies do not penetrate through plant Although fewer pairs of ßies were used in the no- surfaces when they oviposit, so entry into a wider choice Þeld than greenhouse trial, the former used range of plants is likely provided by initial damage older, Þeld-collected ßies compared with the younger, caused by other insects that break through the epi- lab-reared ßies in the latter trial. In general, it would dermis. Goyal et al. (2012) found eggs of C. massyla, be expected that Þeld-collected insects perform better E. eluta, and E. stigmatias were not able to complete than lab reared ones if other variables (e.g., age, sex) their development to adults on sugarcane (Saccharum were equal. Glas et al. (2007) showed that Þeld-col- officinarum L.) stalks until holes were drilled into lected Chilo partellus (Swinhoe) (Lepidoptera: Pyr- them. Two studies conducted by Frõ´as (1981) in Chile alidae) deposited more eggs than laboratory-reared suggested that E. eluta preferred Lepidoptera-infested individuals on maõ´ze and vetivar grass [Vetiveria zi- to uninfested ears. In his Þrst study, E. eluta were zanioides (L.) Nash]. Laboratory-reared Ceratitis found only in ears infested with H. zea larvae; how- capitata (Wiedemann) (Diptera: Tephritidae) had ever, E. eluta and E. annonae were found in both H. lower larval emergence and a shorter preoviposition zea-infested ears and undamaged ears in his second period compared with those of Þeld-collected ßies study. (Ro¨ssler 1975). However, our studies on the develop- The results of our trials may indicate the presence ment and reproduction of C. massyla and Euxesta spp. of attractive olfactory cues in ears damaged by Lep- later determined that egg deposition increases to its idoptera larvae that results in signiÞcantly greater ovi- maximum around 10Ð13 d after adult eclosion and position in infested compared with uninfested ears. then decreases toward the end of their adult life Rojas (1999) found that Mamestra brassicae (L.) (Lep- (Goyal 2010). Therefore, even with the assumption of idoptera: Noctuidae) deposited signiÞcantly more a uniform age distribution with the subsample of Þeld- October 2012 GOYAL ET AL.: PEST STATUS OF PICTURE-WINGED FLIES INFESTING CORN 1137 collected ßies used in 2007, these adults likely pro- Arce de Hamity, M. G. 1986. Biologia de Euxesta eluta (Dip.: duced fewer eggs than ßies within their peak repro- Ulididae). Comportamiento en el ataque y putrefaccion ductive period obtained from our laboratory colony. de las espigas de maiz. Acta Zool. Lilloana 38: 119Ð128. In summary, all three picture-winged ßy species Bailey, W. K. 1940. Experiments in controlling corn ear deposited eggs and developed readily on uninfested pests in Puerto Rico. P.R. Agric. Exp. Stn. Circular no. 23. ears as well as on those previously attacked by Diptera Barber, G. W. 1939. Injury to sweet corn by Euxesta stig- and Lepidoptera pests. More ßies of all three species matias Loew in southern Florida. J. Econ. Entomol. 32: 879Ð880. emerged from ears that were infested with S. fru- Barbosa, P., A. E. Segarra-Carmona, and W. Colo´n-Guasp. giperda larvae than uninfested ears in choice tests, 1986. Eumecosomyia nubila (Wiedemann), a new otitid suggesting either preference for or greater survival in Puerto Rico, with notes on the habits of the dipteran within ears previously infested with such larvae. The species complex of corn. J. Agric. Univ. P.R. 70: 155Ð156. results suggest that presence of S. frugiperda damage Chittenden, F. H. 1911. Some insects injurious to truck in corn Þelds could attract ßies resulting in a greater crops. Notes on various truck-crop insects. U. S. Dep. population of ßies and even greater damage to ears Agric. Bur. Entomol. 82: 90Ð90. than in Þelds without army- or earworm damage. Chittenden, F. H. 1927. Tritoxa flexa Wied., the black onion Interviews with local pest control advisors conÞrmed ßy (Ortalidae, Dipt.). Can. Entomol. 59: 1Ð4. that Þelds heavily infested with S. frugiperda before Crombie, A. 1944. On intraspeciÞc and interspeciÞc com- tassel push are more likely to experience greater num- petition in larvae of granivorous insects. J. Exp. Biol. 20: bers of picture-winged ßies than Þelds with low levels 135Ð51. Frıas, D. L. 1981. Diferencias de microhabitats entre Eux- of these Lepidoptera pests (G. N., unpublished data). ´ esta eluta y Euxesta annonae (Diptera, Otitidae). Agric. Therefore, control measures for S. frugiperda before Tech. (Chile). 41: 89Ð94. the sensitive ear stage may help to reduce the relative Glas, J. J., J. van den Berg, and R.P.J. Potting. 2007. Effect of attraction of ßies to sweet corn Þelds. However, our learning on the oviposition preference of Þeld-collected experience also indicates that ears in Þelds of standard, and laboratory-reared Chilo partellus (Lepidoptera: as well as Bacillus thuringiensis-enhanced sweet corn Crambidae) populations. Bull. Entomol. Res. 97: 415Ð420. varieties, with no or very low levels of S. frugiperda Goyal, G. 2010. Morphology, Biology and distribution of feeding damage can still become 100% infested by corn-infesting picture-winged ßies. Ph.D. dissertation, these ßies if not treated with insecticides in southern University of Florida, Gainesville. Florida. Likewise, secondary ears left on plants at Goyal, G., G. S. Nuessly, G. J. Steck, D. R. Seal, J. L. Capinera, harvest to be eventually harvested as silage provide and K. J. Boote. 2010. New report of Chaetopsis massyla untreated reservoirs of ears (both infested and unin- (Diptera: Ulidiidae) as a primary pest of corn in Florida. Fla. Entomol. 93: 198Ð202. fested with army- and earworms) for ulidiid popula- Goyal, G., G. S. Nuessly, D. R. Seal, J. L. Capinera, G. J. Steck, tion development. Chaetopsis massyla, E. eluta, and E. and K. J. Boote. 2011a. Distribution of picture-winged stigmatias should be considered primary pests of sweet ßies (Diptera: Ulidiidae) infesting corn in Florida. Fla. corn. Entomol. 94: 35Ð47. Goyal, G., G. S. Nuessly, G. J. Steck, J. L. Capinera, and D. R. Seal. 2011b. Comparative morphology of the immature stages of three corn-infesting Ulidiidae (Diptera). Ann. Acknowledgments Entomol. Soc. Am. 104: 416Ð428. We thank I. Alanzo, H. K. Gill, M. Gonzalez, N. Larsen, F. Goyal, G., G. S. Nuessly, D. R. Seal, G. J. Steck, J. L. Capinera, Sosa, and J. Terry for assistance with Þeld studies and ßy and K. J. Boote. 2012. Alternative plants for develop- colony maintenance. This research was made possible by a ment of picture-winged ßy pests of maize. Entomol. Exp. Hand Fellowship from the Dolly and Homer Hand Group, Appl. 143: 177Ð184. and a Warren Wood Scholarship from the Miami-Dade Hawley, I. M. 1922. The sugar-beet root maggot (Tetanops County Agri-Council. aldrichi Hendel), a new pest of sugar-beets. J. Econ. Entomol. 15: 388Ð391. Hayslip, N. C. 1951. Corn-silk ßy control on sweet corn, pp. 1Ð6. Univ. Fla. Agric. Exp. Stn. Circ. S-41, Gainesville, FL. References Cited Hentz, M. G., and G. S. Nuessly. 2004. A technique for rear- Allen, E. J., and B. A. Foote. 1967. Biology and immature ing the sweet corn pest, Euxesta stigmatias (Diptera: Otiti- stages of three species of Otitidae (Diptera) which have dae), on a Helicoverpa diet. J. Entomol. Sci. 39: 140Ð143. saprophagous larvae. Ann. Entomol. 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