Attraction, Oviposition Preferences, and Olfactory Responses of Corn-Infesting Ulidiidae (Diptera) to Various Host-Based Substrates.

Fresh market sweet corn (Zea mays L., convar. saccharata var. rugosa, Poales: Poaceae) ears produced in Florida are damaged by the larvae of Euxesta stigmatias Loew, Euxesta eluta Loew, and Chaetopsis massyla Walker (Diptera: Ulidiidae) that renders ears unmarketable. No standard lure exists for monitoring these pests. Oviposition substrate and attractant bioassays were designed to identify attractive substrates for further semiochemical investigation. Frass from the fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), was more attractive than other ovipositional substrates tested for E. eluta and C. massyla, and resulted in greater ovipositional output. Tassel-derived armyworm frass was more attractive than leaf-derived frass for oviposition. Frass also resulted in greater oviposition output by two species. In attraction bioassays, frass was generally preferred over the corresponding corn tissue, and only C. massyla demonstrated a preference for silk-frass over tassel-frass. The most promising substrates were then evaluated by electroantennography (EAG) to quantify olfactory responses. Frass volatiles also elicited greater antennal responses than corn volatiles. With tassel-frass, greater amplitude EAG responses were recorded from immature E. eluta female antennae, while mature female E. stigmatias exhibited greater responses. Equivalent antennal response to silk-frass was observed from E. eluta. Overall, silk-frass elicited the greatest EAG responses among all three fly species. Our results indicate that armyworm frass is an important resource in the chemical ecology of corn-infesting silk flies, and this substrate warrants further investigation for potential attractants that may facilitate development of novel management tools for these pests.

Host Selection, Growth, and Survival of Melonworm (Lepidoptera: Crambidae) on Four Cucurbit Crops Under Laboratory Conditions.

The melonworm, Diaphania hyalinata L. (Lepidoptera: Crambidae), is one of the most serious insect problems affecting cucurbit production. We evaluated the relative preference and suitability of yellow squash, zucchini, cucumber, and watermelon to melonworm by measuring its oviposition, larval feeding preference, survivorship, and developmental responses in the laboratory. Whole plants were used for oviposition study, whereas host leaf discs were used for all the other studies. Watermelon feeding resulted in the longest larval development period (14.3 d), greatest prepupal weights and survivals rates (92%; first instar to adult) among the four crops. However, for watermelon, adult oviposition preference (199.5 eggs/♀), egg survival (70%), and larval feeding (4.1% defoliation) were numerically or statistically lowest, and larval head capsule widths and whole-body lengths were smallest. When differences occurred among these variables, yellow squash, zucchini, and cucumber were each typically higher (or quicker to develop) than watermelon. So why do melonworm adults not prefer watermelon, or at least select it as frequently as squash and cucumber when ovipositing? The answer likely is that there might be some variation in the important chemical components among these cucurbits. We suggest that comparison of kairomones and allomones from watermelon and related cucurbits would be very useful for determining the combination resulting in the lowest risk of damage to the more susceptible cucurbits (assuming the levels can be modified without seriously affecting the crops).

Variable Pyrethroid Susceptibility Among the Sweet Corn-Infesting Ulidiidae (Diptera) in Florida and New Baseline Susceptibilities.

Florida sweet corn is intensively treated to prevent infestation from the corn-infesting picture-winged fly complex (hereafter referred to as silk flies, Diptera: Ulidiidae). Previous bioassays performed on Euxesta stigmatias Loew demonstrated some pyrethroids performed weakly, while others were more efficacious and with longer-lasting residual activity. Since the last published bioassays, new active ingredients have been made available, other species in the complex discovered, and label restrictions increased for some products. For these reasons, topical bioassays were performed on the three most common species to assess insecticide efficacy of current commercial products labeled for either silk fly or fall armyworm ( Spodoptera frugiperda (J.E. Smith), Lepidoptera: Noctuidae) control. Bioassays were conducted using formulated product mixed in water and applied using a Generation III Research Spray Booth. The median lethal concentration ratio (LC 50 ) of beta-cyfluthrin with and without the pyrethroid synergist piperonyl butoxide was investigated. Acetamiprid, chlorantraniliprole, carbaryl, and flubendiamide did not result in high mortality to any species tested. Euxesta eluta Loew was susceptible to all other insecticides tested, and exhibited the lowest LC 50 to beta-cyfluthrin. Both Chaetopsis massyla Walker and E. stigmatias recovered from several pyrethroid treatments. Euxesta stigmatias also had the highest beta-cyfluthrin LC 50 , and piperonyl butoxide restored beta-cyfluthrin efficacy and lowered the LC 50 s of all three species.

Distribution of Zelus longipes (Hemiptera: Reduviidae) in south Florida corn fields and its functional response to corn-infesting picture-winged flies (Diptera: Ulidiidae).

The milkweed assassin bug, Zelus longipes (L.) (Hemiptera: Reduviidae), is a generalist predator and a potential biological control agent of picture-winged flies (Diptera: Ulidiidae), which cause considerable economic damage to sweet corn yields in Florida. We studied the potential of Z. longipes as a biocontrol agent of four ulidiid pests in corn fields: Euxesta stigmatias Loew, Euxesta eluta Loew, Euxesta annonae F., and Chaetopsis massyla Walker. Within-plant and within-field distributions of Z. longipes and ulidiids and functional responses of Z. longipes to ulidiid prey were determined. Highest numbers of Z. longipes and ulidiids in the R1, R2, and R3 corn stages were generally in the basal or middle leaves at 09:00 h EST, ears at 13:00 h EST, and top and tassel at 17:00 h EST. Hence, there seemed to be a coordinated migration of Z. longipes and ulidiids from the lowest to the highest parts of the corn plant during the day. Within the corn field, aggregated (clumped) distributions were most common for Z. longipes and ulidiids especially in the later R2 and R3 stages based on Taylor's power law, Iwao's patchiness regression, index of dispersion, and Lloyd's patchiness indices of dispersion. However, predator and prey populations were lower in the R1 stage, and there were inconsistent results for dispersion indices among times of day and between predators and prey. Ulidiid distributions in R1 were mostly regular (uniform) at 13:00 h EST, but aggregated at 09:00 h and 17:00 h. However, Z. longipes R1 distributions were mostly aggregated at 13:00 h, but random or regular at 09:00 h and 17:00 h EST. Handling times for male and female Z. longipes were 1.0-1.39 h and 0.67-0.97 h, respectively, and each had a type II functional response to E. stigmatias, E. eluta, and E. annonae and consumed about five flies per day. Although the population abundance of Z. longipes can vary between seasons, it appears to be a promising biocontrol agent of ulidiid flies in corn.

Biology and biotype determination of greenbug, Schizaphis graminum (Hemiptera: Aphididae), on seashore paspalum turfgrass (Paspalum vaginatum).

Greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), was first discovered damaging seashore paspalum (Paspalum vaginatum Swartz) turfgrass in November 2003 at Belle Glade, FL. Inquiries to several golf courses with seashore paspalum turf across southern Florida indicated infestation was wide spread by April 2004. Damage symptoms progress from water soaked lesions surrounding feeding sites within 24 h to chlorosis and necrosis of leaf tips within 96 h. Problems caused by greenbug feeding were initially misdiagnosed as fertilizer, disease, other insects, or water management problems because aphids were not previously found on warm season turfgrasses. Greenbug development and fecundity studies were conducted on six seashore paspalum varieties: 'Aloha,' 'SeaDwarf,' 'SeaGreen,' 'SeaIsle,' 'SeaWay,' and 'SeaWolf.' Greenbug did not survive on 'SeaWolf.' Development rates (mean +/- SEM) ranged from 7.6 +/- 0.2 to 8.2 +/- 0.2 d on the remaining varieties. Greenbug longevity and fecundity on 'Aloha' were significantly less than on the other varieties. The estimated intrinsic rate of natural increase (r(m)) for greenbug ranged from 0.24 to 0.26 across tested varieties. Values for net reproductive rate (R(o)) ranged from 12.3 on 'Aloha' to 40.4 on 'SeaWay.' In feeding trials on indicator plants, the Florida isolate of greenbug exhibited a unique biotypic profile most commonly found on noncultivated grass hosts. It was virulent on the wheat variety GRS1201 that is resistant to the principal agricultural biotypes attacking small grains and to all currently available resistant sorghum varieties.

Resistance to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Euxesta stigmatias (Diptera: Ulidiidae) in sweet corn derived from exogenous and endogenous genetic systems.

Field trials using Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) and Euxesta stigmatias Loew (Diptera: Ulidiidae) were conducted to evaluate resistance and potential damage interactions between these two primary corn, Zea mays L., pests against Lepidoptera-resistant corn varieties derived from both endogenous and exogenous sources. The endogenous source of resistance was maysin, a C-glycosyl flavone produced in high concentrations in varieties 'Zapalote Chico 2451' and 'Zapalote Chico sh2'. The exogenous resistance source was the Bacillus thuringiensis (Bt)11 gene that expresses Cry1A(b) insecticidal protein found in 'Attribute GSS-0966'. Damage by the two pests was compared among these resistant varieties and the susceptible 'Primetime'. Single-species tests determined that the Zapalote Chico varieties and GSS-0966 effectively reduced S. frugiperda larval damage compared with Primetime. E. stigmatias larval damage was less in the Zapalote Chico varieties than the other varieties in single-species tests. E. stigmatias damage was greater on S. frugiperda-infested versus S. frugiperda-excluded ears. Ears with S. frugiperda damage to husk, silk and kernels had greater E. stigmatias damage than ears with less S. frugiperda damage. Reversed phase high-performance liquid chromatography analysis of nonpollinated corn silk collected from field plots determined that isoorientin, maysin, and apimaysin plus 3'-methoxymaysin concentrations followed the order Zapalote Chico sh2 > Zapalote Chico 2451 > Attribute GSS-0966 = Primetime. Chlorogenic acid concentrations were greatest in Zapalote Chico 2451. The two high maysin Zapalote Chico varieties did as well against fall armyworm as the Bt-enhanced GSS-0966, and they outperformed GSS-0966 against E. stigmatias.