Gregg S. Nuessly

Resistance to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Euxesta stigmatias (Diptera: Ulidiidae) in Sweet Corn Derived from Exogenous and Endogenous Genetic Systems

Abstract 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 CryIA(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.

INSECTS ASSOCIATED WITH FABA BEAN, VICIA FABA (FABALES: FABACEAE), IN SOUTHERN FLORIDA

Abstract One hundred faba bean (Vicia faba L., Fabales: Fabaceae) accessions from the USDA-NSSL Seed Repository in Prosser, WA were grown outdoors in southern Florida from December 2000 through April 2001 and October 2001 through April 2002 to both evaluate their potential as a forage crop and to initiate selections of superior genotypes. Insect herbivores and their predators were observed for feeding associations and collected for identification throughout the two seasons of trials. Sixty-one species of insect herbivores and nectaring predators and parasitoids were observed feeding on or were captured on faba bean leaves, stems, flowers, extra-floral nectaries or pods. Additionally, thirty-two species of predacious and parasitic insects were observed eating herbivorous insects or captured while searching for prey or hosts on faba beans plants. The most significant damage was caused by large populations of Aphis craccivora Koch (Hemiptera: Aphidae) that fed on terminals and young leaf and stem tissue. Six Coccinellidae species fed upon aphids and reproduced on the crop. Pods were damaged by reproducing populations of Leptoglossus phyllopus (L.) (Hemiptera: Coreidae) and Nezara viridula (L.) (Hemiptera: Pentatomidae).

Effects of Fall Armyworm (Lepidoptera: Noctuidae) Interstrain Mating in Wild Populations

Abstract Fall armyworm is a significant agricultural pest in the United States, affecting most notably sweet corn and turfgrass. Two morphologically identical strains, rice strain (R-strain) and corn strain (C-strain), exist that differ physiologically and behaviorally and can be identified by mitochondrial haplotyping. Recent studies of overwintering populations in Florida indicate that the mitochondrial lineage associated with the R-strain itself consists of two genetically distinct subgroups, with one having molecular markers consistent with interstrain hybridization between R-strain females and C-strain males. To test this possibility and examine the ramifications of interstrain mating on population behavior and strain fidelity, larvae and adult males were tested for genetic marker combinations representative of the host strains and potential hybrids. These studies showed a sexually dimorphic distribution pattern for a sex-linked marker that is a predicted result of interstrain mating. Despite evidence of substantial interbreeding in the overwintering sites, both FR and the strain-diagnostic mitochondrial markers still showed the plant host and habitat biases associated with the host strains, indicating that strain integrity was largely maintained. However, there is evidence that the two R-strain subpopulations differ in habitat distribution in a manner suggestive of the “hybrid” genotype being less specific in its plant host preference. The existence of a genetically distinct hybrid subpopulation must be taken into account when evaluating fall armyworm population dynamics and infestation patterns in overwintering areas.

Efficacy of emamectin benzoate and Bacillus thuringiensis at controlling diamondback moth (Lepidoptera: Plutellidae) populations on cabbage in Florida

Emamectin benzoate (MK-244; Merck & Co., Rahway, NJ), used alone and alternated with Bacillus thuringiensis (Berliner) ssp. aizawai (Bta), Bta alone, and B. thuringiensis ssp. kurstaki (Btk) alone, were evaluated for control of diamondback moth, Plutella xylostella (L.), in head cabbage at three locations in Florida. Additional treatments unique to each location were also evaluated. Emamectin benzoate alone, Bta alone, emamectin benzoate alternated with Bta, and mevinphos were shown to be effective. Btk was less efficacious than Bta at two locations.

Biology and Biotype Determination of Greenbug, Schizaphis graminum (Hemiptera: Aphididae), on Seashore Paspalum Turfgrass (Paspalum vaginatum)

Abstract 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 (rm) for greenbug ranged from 0.24 to 0.26 across tested varieties. Values for net reproductive rate (Ro) 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.

Development, longevity, and fecundity of Sipha flava (Homoptera: Aphididae) feeding on Sorghum bicolor

Abstract Sipha flava is a serious pest in sugarcane in southern Florida, so efforts in better understanding its biology were initiated. Development, longevity, and fecundity of alate and apterous S. flava (Forbes) feeding on Sorghum bicolor [L.] Moench., cultivar ‘Kow Chow,’ were examined under near-ambient temperature and lighting conditions within a glasshouse. After examining several body dimensions during apterous aphid development (antennal length, head width, body length, and abdominal width), antennal length was found to be the best indicator of an instar. Apterous aphids completed development from nymph to adult in ≈8 d and passed through four instars. A comparison between the sizes of apterous and alate morphs indicated that apterous females were larger and weighed more than the alates. Both morphs survived equally as long during reproduction (21 d) but produced slightly different numbers of nymphs over their life (apterous = 54.3, alate = 48.2). During the first 8 d of reproduction, apterous adults produced 3.3 nymphs/d and alates produced 2.3 nymphs/d. However, during the following 8 d, nymphal production by apterous females dropped to 2.7 nymphs/d but increased to 2.9 nymphs/d by alates. The estimated intrinsic rate of natural increase (rm) for apterous aphids was 0.314. The net reproductive rates (Ro) for alate and apterous adults based on 0% nymphal mortality were 45.80 and 53.09 and for 21% nymphal mortality were 36.3 and 41.9, respectively.

Temperature-Dependent Development of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on Sugarcane Under Laboratory Conditions

ABSTRACT Lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), is an important sugarcane pest in southern Florida. Development of immature stages (eggs, larvae, prepupae, and pupae) of lesser cornstalk borer was observed on sugarcane at constant temperatures (13, 15, 18, 21, 24, 27, 30, 33, and 36°C), 65–70% RH, and a photoperiod of 14:10 (L:D) h. Total development (from egg deposition to adult emergence) ranged from 22.8 ± 0.3 d at 33°C to 120.7 ± 2.8 d at 13°C. Lesser cornstalk borer required 543.48 DD to complete development. Developmental time decreased with increase in temperature from 13 to 33°C and increased markedly at 36°C in all immature stages. One linear and six nonlinear models used to model insect development (Briere-1, Briere-2, Logan-6, Lactin, Taylor, and polynomial models) were tested to describe the relationship between temperature and developmental rate (d-1). Criteria used to select the best model were the greatest r2, lowest residual sum of squares (RSS), and Akaike information criterion values. The Briere-1 model fit the data best and provided the best estimates of developmental temperature thresholds for all immature stages on sugarcane. The estimated lower and upper developmental thresholds for total development were 9.3 ± 1.8 and 37.9 ± 0.7°C, respectively. The optimal temperature estimated for the total development was 31.39 ± 0.9°C. Based on these results, we can forecast the different stages of lesser cornstalk borer at different times in sugarcane. This will enable us to choose the best time to control this pest with greater precision.

Geographic Population Structure of the Sugarcane Borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), in the Southern United States

The sugarcane borer moth, Diatraea saccharalis, is widespread throughout the Western Hemisphere, and is considered an introduced species in the southern United States. Although this moth has a wide distribution and is a pest of many crop plants including sugarcane, corn, sorghum and rice, it is considered one species. The objective was to investigate whether more than one introduction of D. saccharalis had occurred in the southern United States and whether any cryptic species were present. We field collected D. saccharalis in Texas, Louisiana and Florida in the southern United States. Two molecular markers, AFLPs and mitochondrial COI, were used to examine genetic variation among these regional populations and to compare the sequences with those available in GenBank and BOLD. We found geographic population structure in the southern United States which suggests two introductions and the presence of a previously unknown cryptic species. Management of D. saccharalis would likely benefit from further investigation of population genetics throughout the range of this species.

REPELLENCY OF THE BIOPESTICIDE, AZADIRACHTIN, TO WIREWORMS (COLEOPTERA: ELATERIDAE)

ABSTRACT The neem tree Azadirachta indica A. Juss produces numerous allelochemical compounds. The most effective active ingredient in A. indica based insecticides is azadirachtin. We found that azadirachtin did not cause mortality, antifeeding responses, or change growth rate of Melanotus communis (Gyllenhal) wireworms. However, azadirachtin treated soil was repellent to the wireworms. This is the first report of azadirachtin being repellent to any of the large and economically important family of Elateridae.

Differential Probing Response of Serpentine Leafminer, Liriomyza trifolii (Burgess), on Cos Lettuce

Leaf mining damage by serpentine leafminers, Liriomyza trifolii (Burgess) (Diptera: Agromyzidae), is a major problem of many leafy vegetables especially lettuce. A hierarchy of leaf probing prefere...