Feeding Bioassays Research Articles

Laboratory and field evaluation of rodent bait treated with fipronil for feed through and systemic control of Phlebotomus papatasi

The sand fly Phlebotomus papatasi is the main vector of Leishmania major, etiologic agent of zoonotic cutaneous leishmaniasis (ZCL), which is endemic in North Africa, the Middle East, and Asia. In North Africa, Meriones shawi is one of the two main reservoir hosts of L. major. P. papatasi populations are maintained in borrowing rodents such as M. shawi. Three fipronil-treated rodent baits were evaluated for systemic and feed through insecticidal activity against P. papatasi feeding on M. shawi. Through blood feeding bioassays, mortality rates of females P. papatasi increased with the concentration of fipronil in the rodent bait varying from 0.001% to 0.005%. In the laboratory, more than 90.0% of P. papatasi were killed within 48h after blood feeding on the desert's jirds, M. shawi, treated up to 29 days prior with a single application of fipronil at a concentration of 0.001%, 0.0025% and 0.005%. Through larval bioassays, mortality rates of larvae that have fed on faeces of treated bait for M. shawi increase with the concentrations of fipronil. Faeces of orally-treated Meriones were significantly toxic to larvae for 5 weeks with a concentration of 0.005%. In the field, application of treated bait resulted in 80.0% reduction in the populations of P. papatasi up to 6 weeks after a single application of fipronil at a concentration of 0.005%. This is the first study to demonstrate field efficacy of fipronil-treated rodent baits for P. papatasi control and the first study to evaluate this approach in M. shawi, a principal ZCL reservoir host. These results suggest that fipronil-treated rodent baits can be used to effectively reduce the populations of P. papatasi associated with M. shawi in ZCL endemic areas.

An Inexpensive Feeding Bioassay Technique for Stored-Product Insects

ABSTRACT We used the red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), to compare three feeding bioassay techniques using flour disks. The area (scanner or digital photographs) and mass (sensitive balance) of the same flour disks were measured daily for 1 or 2 wk to assess feeding by insects. The loss in mass and area over 4 h was measured, as some variation over time was noticed in the disks with no insects feeding on them. The gravimetric method correlated well with both measurements of the area for the disks held in a growth chamber: scanner (R2 = 0.96), digital photography (R2 = 0.96). There was also a high correlation (R2 = 0.86) between the disk weight and area scanned at normal lab conditions. There were differences in the percentage of the disks remaining over time depending on the temperature and whether they were weighed or scanned. Measuring the mass of the disks resulted in a relatively larger percent of disk remaining compared with the scanned area. Mass measurements required a sensitive balance, handling of the disks and the insects, and appeared slightly more sensitive to humidity and temperature changes over time. Scanning the disks requires flat bed scanner access but less handling of both insects and disks. Digital photographs could be taken quickly, requiring less equipment, although photographs had to be further processed to determine area Scanning or taking digital photographs of flour disk area was an effective technique for measuring insect feeding.

Indoor Application of Attractive Toxic Sugar Bait (ATSB) in Combination with Mosquito Nets for Control of Pyrethroid-Resistant Mosquitoes

BackgroundAttractive toxic sugar bait (ATSB) sprayed onto vegetation has been successful in controlling Anopheles mosquitoes outdoors. Indoor application of ATSB has yet to be explored. The purpose of this study was to determine whether ATSB stations positioned indoors have the potential to kill host-seeking mosquitoes and constitute a new approach to control of mosquito-borne diseases.MethodsInsecticides were mixed with dyed sugar solution and tested as toxic baits against Anopheles arabiensis, An. Gambiae s.s. and Culex quinquefasciatus in feeding bioassay tests to identify suitable attractant-insecticide combinations. The most promising ATSB candidates were then trialed in experimental huts in Moshi, Tanzania. ATSB stations were hung in huts next to untreated mosquito nets occupied by human volunteers. The proportions of mosquitoes killed in huts with ATSB treatments relative to huts with non-insecticide control treatments huts were recorded, noting evidence of dye in mosquito abdomens. ResultsIn feeding bioassays, chlorfenapyr 0.5% v/v, boric acid 2% w/v, and tolfenpyrad 1% v/v, mixed in a guava juice-based bait, each killed more than 90% of pyrethroid-susceptible An. Gambiae s.s. and pyrethroid-resistant An. arabiensis and Cx. quinquefasciatus. In the hut trial, mortality rates of the three ATSB treatments ranged from 41-48% against An. arabiensis and 36-43% against Cx. quinquefasciatus and all were significantly greater than the control mortalities: 18% for An. arabiensis, 7% for Cx. quinquefasciatus (p<0.05). Mortality rates with ATSB were comparable to those with long lasting insecticidal nets previously tested against the same species in this area. ConclusionsIndoor ATSB shows promise as a supplement to mosquito nets for controlling mosquitoes. Indoor ATSB constitute a novel application method for insecticide classes that act as stomach poisons and have not hitherto been exploited for mosquito control. Combined with LLIN, indoor use of ATSB has the potential to serve as a strategy for managing insecticide resistance.

Susceptibility of Brassicaceous Plants to Feeding by Flea Beetles, &lt;I&gt;Phyllotreta&lt;/I&gt; spp. (Coleoptera: Chrysomelidae)

Crucifer-feeding flea beetles, Phyllotreta spp., are chronic insect pests in Canadian prairie canola production. Multiple laboratory and field feeding bioassays were conducted to determine the susceptibility of a wide range of crucifer species, cultivars, and accessions to feeding by flea beetles with the goal of discovering sources of resistant germplasm. In 62 bioassays of 218 entries, no consistent decreased feeding by flea beetles was seen on any entries of Brassica carinata A. Braun, Brassica juncea (L.) Czern., Brassica napus L., or Brassica rapa L. There was reduced feeding on condiment mustard Sinapis alba L. lines but not on canola-quality lines with reduced amounts of glucosinolates, which were fed on at levels equal to B. napus. Analyses of glucosinolate content found decreased quantities of hydroxybenzyl and butyl glucosinolates in preferred canola-quality S. alba lines and increased levels of hydroxybutenyl glucosinolates compared with levels in condiment S. alba lines. Eruca sativa Mill. was an excellent flea beetle host; Camelina sativa (L.) Crantz lines experienced little feeding. Lines of Crambe abyssinica Hochst. ex R. E. Fries and Crambe hispanica L. had reduced feeding levels compared with Brassica entries, but Crambe glabrata DC did not. The results indicate possible sources of resistance to Phyllotreta flea beetles, while highlighting the complicated roles that glucosinolates may play in Phyllotreta host preference.

Feeding preferences of the weevils Sitona gressorius and Sitona griseus on different lupin genotypes and the role of alkaloids

The weevils Sitona gressorius and Sitona griseus are specialist herbivores on lupins in Europe. The adult weevils feed on the leaves, and the larvae on the root nodules of the plants. This causes severe damage to lupin crops. In the present study, the feeding preferences of lupin weevil adults on different lupin genotypes were examined with respect to a possible effect of lupin alkaloids on host selection. A total of 12 genotypes from the species Lupinus albus, L. angustifolius, L. luteus, and L. nanus were grown in a field experiment and the feeding damage on the leaves caused by naturally occurring lupin weevil adults was estimated. Additionally, a feeding choice test with S. gressorius adults was performed to examine feeding preferences under laboratory conditions. A gas chromatographic analysis provided information on the alkaloid content and profiles in the leaves of the tested lupin genotypes. In the field experiment, significant differences in the extent of the feeding damage within the 12 lupin genotypes were observed. The dual-choice feeding bioassay did not show discrimination of lupin species, but two L. angustifolius genotypes were significantly less affected than the standard L. luteus “Bornal”. The alkaloid analysis revealed large contrasts in alkaloid concentrations and profiles in the leaves of the tested genotypes. Correlation analysis with the results from the field and laboratory did not indicate a significant influence of the total foliar alkaloid content on the extent of weevil feeding.

Dietary Effects of Cotton Tissue Expressing Germin Like Protein on Beet Armyworm (Lepidoptera: Noctuidae) Growth, Survival and Pupation

Transgenic cotton lines that ectopically express a cotton germin-like protein (GLP) were screened for resistance/tolerance factors to the beet armyworm (BAW) Spodoptera exigua (Hübner) via feeding assays. The number of BAW eggs that successfully hatched was not statistically different at 72 h after infestation for wild-type cotton plants (Gossypium hirsutum L. c.v. ‘Coker 312’) or plants of 4 independent transgenic lines (ABP-A, ABPB and ABP-C and ABP-D). However, the damage caused by these same larvae at 72 h was higher for ‘Coker 312’ and line ABP-D when compared to ABP-A, ABP-B and ABP-C transgenic plants. Larval live weights were also significantly higher for Coker 312 and ABP-D at 5, 7, and 14 d when compared to ABP-A, ABP-B and ABP-C. The percentage of larvae that successfully completed pupation was significantly higher for BAW larvae fed ‘Coker 312’ and ABP-D tissue compared to the other 3 lines. These feeding bioassays show the potential for using cotton germin like protein to improve resistance or tolerance for BAW attacking cotton.

Insecticidal Activity and Alkaloid Components of Stemona spp. in Thailand

Stemona species have been traditionally used as natural pesticides and medicinal plants. Despite their diversity, the same vernacular name of “Non Tai Yak” has been used for various species in Thailand because of their similar root shapes. However, a variation in phytochemical constituents of different species was observed, leading to their different biological activities. This study determined the insecticidal activities of various species growing in Thailand. The samples representing 7 species and one unidentified species, probably closely related to S. collinsiae, were tested using chronic feeding bioassays with neonate larvae of the polyphagous pest insect Spodoptera littoralis Boisduval (Lepidoptera, Noctuidae). Potent insect toxicity was observed in all S. collinsiae, the unidentified species, and some samples of S. curtisii. S. kerrii as well as S. aphylla and S. ruprestris showed low to moderate activity. S. tuberosa and S. phyllantha showed no marked insecticidal activity. Stemofoline and didehydrostemofoline were found to be the major compounds in the active samples, clearly demonstrating the higher insecticidal effect than the other alkaloids. Thus, stemofoline and didehydrostemofoline sould be used as bioactive chemical markers for the quality assessment of Stemona roots, their extracts and final products for further pharmaceutical and agricultural developments.

Delayed Toxicity of Two Chitinolytic Enzyme Inhibitors (Psammaplin A and Pentoxifylline) Against Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

By using a no-choice feeding bioassay, delayed toxicity and concentration-dependent mortality of two chitinolytic enzyme inhibitors, pentoxifylline and psammaplin A, were evaluated by determining LT50, LT90, and LT99 (lethal time) against the economically important eastern subterranean termite, Reticulitermes flavipes (Kollar). Pentoxifylline- and psammaplin A-incorporated diets (filter paper) were assayed at 0.01, 0.02, 0.04, 0.08, and 0.21% and 0.0375, 0.075, 0.15, and 0.3% active ingredient (wt:wt), respectively. Acetone-only treated filter paper served as diet for the control treatments. Termite workers were allowed to feed on diet until 100% test population mortality occurred (80-95 d). Both chitinase inhibitors were shown to be toxic to R. flavipes. Concentration-dependent toxicity occurred within the pentoxifylline treatments over the range of 0.01-0.08%, with 0.08% treatments producing an LT50 of 32.2 d. However, mortality in response to psammaplin A treatments lacked concentration-dependent toxicity. Treatment with 0.3% psammaplin A produced an LT50 of 21.3 d. Mortality in response to lower psammaplin A treatments displayed no concentration-dependent trends. This study provides the first report on delayed toxicity of chitinolytic enzyme inhibitors against eastern subterranean termites (order Isoptera) and toxicological data on pentoxifylline and psammaplin A over a range of concentrations.

Innovative Sugar-Insecticide Feeding Bioassay for Adult Female Anopheles gambiae (Diptera: Culicidae)

The primary malaria vector in sub-Saharan Africa, Anopheles gambiae Giles (Diptera: Culicidae), is an anthropophagic and endophilic mosquito targeted for control with insecticides applied to interior resting surfaces and impregnated onto bed net materials. Effective malaria vector management involves monitoring the insecticide susceptibility of mosquito populations. Contemporary bioassays are based on mosquito contact with insecticide residues. We developed an innovative insecticide bioassay system that involves mosquito ingestion of a sugar-insecticide solution. The sucrose-permethrin solution in our bioassay system contained Trypan blue dye, creating a visual marker of insecticide ingestion in the mosquito's abdomen. Blue fecal spots deposited in the bioassay container provided further evidence of mosquito feeding. We used our bioassay to characterize the permethrin susceptibility of adult females of two strains of A. gambiae, one of which was susceptible and the other exhibited reduced susceptibility to permethrin. We compared the dose-response of both strains to permethrin in a forced-contact filter paper bioassay. Both assay approaches produced similar dose-dependent mortality, indicating that the feeding bioassay had appropriately characterized permethrin susceptibility for both mosquito strains.

Insecticidal activity of raw ethanolic extracts from Magnolia dealbata Zucc on a tephritid pest

Ethanolic extracts from Magnolia dealbata (Zucc.) (Magnoliaceae); leaves, bark, seeds, sarcotesta and flowers were evaluated for insecticidal activity against adults of the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae). Using feeding bioassays composed from sugar-extract mixtures, only the extract from sarcotesta indicated insecticidal activity against the flies. The extracts from the other four plant tissues (leaves, bark, seeds and flowers) did not manifest any biological activity. The most effective extract was obtained from oven-dried sarcotesta, whereas extracts from fresh sarcotesta were inactive. Our results suggest that M. dealbata sarcotesta contains secondary metabolites with insecticidal activity against A. ludens adults. These metabolites are as potent as natural pyrethins and represent a potential substance for controlling this type of pest.

Occurrence ofDiaphorina citri(Hemiptera: Liviidae) in an Unexpected Ecosystem: The Lake Kissimmee State Park Forest, Florida

The current investigation describes the capture of Asian citrus psyllid (ACP), Diaphorina citri, in an unexpected ecosystem, the Lake Kissimmee State Park forest. In this forest, occurrence of citrus is particularly rare, and no Rutaceae were found within the trapping locations or in nearby (≈500 m) areas. In addition to trap capture data, complementary laboratory no-choice feeding bioassays suggest that ACP may have a broader alternative plant feeding range than previously thought, which may allow for significant dispersal even through dense forests in Florida up to 2.3 km from large-area plantings of citrus.

Implementation of an Indoxacarb Susceptibility Monitoring Program Using Field-Collected German Cockroach Isolates From the United States

Indoxacarb, a sodium channel-blocking insecticide, has been in widespread use for German cockroach control in the United States since 2006. A two-tiered indoxacarb susceptibility monitoring strategy was previously developed as a first step toward determining indoxacarb susceptibility levels in German cockroach field populations. This strategy entails: (tier 1) testing field-collected populations in vial bioassays at two diagnostic concentrations; and (tier 2) testing populations at three diagnostic doses in oral (feeding) bioassays with treated bait matrix. In the current study the two-tiered technique was implemented to evaluate field (n = 14) and susceptible laboratory (n = 2) strains collected from 13 different U.S. locations. Our hypothesis was that at least some of the field-collected populations would display significant survivorship in both bioassays relative to susceptible laboratory populations. In agreement with this hypothesis, significantly reduced susceptibility was detected in 13 and 7 field strains with vial and feeding bioassays, respectively. In general, the lower number of strains displaying reduced susceptibility in feeding bioassays (seven strains) supports previous findings that indoxacarb is more toxic via ingestion. Although these findings suggest a reduced risk for resistance selection via feeding on indoxacarb-containing baits, they also suggest a need for proactive resistance management with respect to both spray and bait products.

Lipophilic Defenses From Alcyonium Soft Corals of Antarctica

Alcyonacean soft corals lack physical or skeletal defenses and their nematocyst system is weak, leading to the conclusion that soft corals mainly rely on chemistry for protection from predators and microbes. Defensive chemicals of primary and secondary metabolic origin are exuded in the mucus surface layer, explaining the general lack of heavy fouling and predation in corals. In Antarctic ecosystems, where generalist predation is intense and mainly driven by invertebrate consumers, the genus Alcyonium is represented by eight species. Our goal was to investigate the understudied chemical ecology of Antarctic Alcyonium soft corals. We obtained six samples belonging to five species: A. antarcticum, A. grandis, A. haddoni, A. paucilobulatum, and A. roseum, and assessed the lipid-soluble fractions for the presence of defensive agents in these specimens. Ethyl ether extracts were tested in feeding bioassays with the sea star Odontaster validus and the amphipod Cheirimedon femoratus as putative sympatric predators. Repellent activities were observed towards both consumers in all but one of the samples assessed. Moreover, three of the extracts caused inhibition to a sympatric marine bacterium. The ether extracts afforded characteristic illudalane sesquiterpenoids in two of the samples, as well as particular wax esters subfractions in all the colonies analyzed. Both kinds of metabolites displayed significant deterrent activities demonstrating their likely defensive role. These results suggest that lipophilic chemicals are a first line protection strategy in Antarctic Alcyonium soft corals against predation and bacterial fouling.

The impact of secondary compounds and functional characteristics on lichen palatability and decomposition

Summary There has been much recent interest in understanding how functional traits of vascular plant species drive ecological processes such as herbivory and litter decomposition. In plants, these two processes are often driven by the same or similar suites of traits and therefore correlate across species. However, few studies have considered how traits of plant‐like life forms such as lichens determine species differences in their effects on ecological processes. This is despite the significant contribution of lichens to carbon and nutrient cycling in many environments. We collected 28 lichen species that differed in their growth form, substrate type and capacity to fix N, and determined key traits for each species. For each species, we performed a feeding bioassay using the generalist snail Cepaea hortensis and carried out a laboratory bioassay to assess decomposability. We did these tests both with intact lichen material containing natural concentrations of carbon‐based secondary compounds (CBSCs), and material that had been acetone rinsed to reduce concentrations of CBSCs, to evaluate the effect of CBSC on palatability and decomposability. We found that reducing CBSC concentrations greatly increased palatability for 17 species, and decomposability of 10 species. However, decomposability was correlated with several lichen traits while palatability was not, regardless of whether or not CBSCs were removed, and we therefore found no relationship between decomposability and palatability across species. Decomposability and palatability both varied, but in contrasting directions, among N‐fixing vs. non‐fixing lichens, lichens with different growth forms and those from contrasting substrate types. As such, N‐fixing lichens had higher decomposition rates but lower consumption rates than non‐fixing lichens, while foliose species had higher decomposition rates but lower consumption rates than fruticose species. Synthesis: We have shown that lichen CBSCs regulate key processes such as lichenivory and decomposition, that lichen decomposability but not palatability are related to traits, and that these two processes are unrelated across species. These results highlight the potential role of lichen species differences in influencing ecosystem processes relating to decomposition and nutrient cycling and the role that grazers may play in driving this.

Baseline Responses ofAlphitobius diaperinus(Coleoptera: Tenebrionidae) to Insect Growth Regulators

J. Agric. Urban Entomol. 29: 35-54 (2013) ABSTRACT The cancellation of most organophosphate and carbamate insecticides, and the emerging resistance to currently available insecticides for managing the lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), necessitate efficacy studies on other classes of insecticidal compounds. Baseline dose-response bioassays were conducted with three different types of insect growth regulators (IGRs), fenoxycarb, diflubenzuron, and 20-hydroxyecdysone (20E) on first and seventh instars, two day-old pupae, and one-week-old adult beetles. Insects were exposed to a range of concentrations through topical application, by residual contact with treated wood shavings, and through feeding on treated chicken feed diet. Insects were observed at 10-day intervals to estimate mortality, pupation, and abnormal growth for each treatment. The mean number of days to pupation increased and pupation was delayed in fenoxycarb-treated seventh instars in feeding, residual, and topical bioassays. Fenoxycarb-treated larvae continued to molt and gain weight, and died as deformed larvae, abnormal pupae, or intermediate larval-pupal and pupal-adult forms. In feeding bioassays, fenoxycarb was more toxic to seventh instars than to first instars or adults, whereas diflubenzuron was more toxic to first instars than it was to seventh instars or adults. The feeding bioassay was more suitable for the first and seventh instars, although the residual contact bioassay could also be used for seventh instars. Adults succumbed to lower concentrations of IGRs in a topical bioassay than in feeding or residual bioassays. All three bioassay methods produced usable dose-response curves and may be used for surveying temporal changes in the IGR susceptibility to lesser mealworm.

Proof of concept for a novel insecticide bioassay based on sugar feeding by adult Aedes aegypti (Stegomyia aegypti)

Aedes aegypti L. (Stegomyia aegypti) (Diptera: Culicidae) is the principal vector of dengue and yellow fever viruses in tropical and subtropical regions of the world. Disease management is largely based on mosquito control achieved by insecticides applied to interior resting surfaces and through space sprays. Population monitoring to detect insecticide resistance is a significant component of integrated disease management programmes. We developed a bioassay method for assessing insecticide susceptibility based on the feeding activity of mosquitoes on plant sugars. Our prototype sugar-insecticide feeding bioassay system was composed of inexpensive, disposable components, contained minimal volumes of insecticide, and was compact and highly transportable. Individual mosquitoes were assayed in a plastic cup that contained a sucrose-permethrin solution. Trypan blue dye was added to create a visual marker in the mosquito's abdomen for ingested sucrose-permethrin solution. Blue faecal spots provided further evidence of solution ingestion. With the sugar-insecticide feeding bioassay, the permethrin susceptibility of Ae. aegypti females from two field-collected strains was characterized by probit analysis of dosage-response data. The field strains were also tested by forced contact of females with permethrin residues on filter paper. Dosage-response patterns were similar, indicating that the sugar-insecticide feeding bioassay had appropriately characterized the permethrin susceptibility of the two strains.

Alkaline cooking (nixtamalisation) and the reduction in the in vivo toxicity of fumonisin-contaminated corn in a rat feeding bioassay

Nixtamalisation is a widely used food processing method in which whole kernel corn is cooked and steeped in alkaline water. It reduces the amount of fumonisin B1 (FB1) that can be detected after cooking. However, the fate of FB1 during nixtamalisation is not fully understood and potentially toxic reaction products, including matrix-associated “masked” FB1 forms that are not detected by routine analytical methods might remain in nixtamalised corn. To assess how nixtamalisation of whole kernel corn affects fumonisin toxicity, male rats were fed diets containing low, mid or high levels of uncooked (LU, MU, HU) or alkaline cooked (LC, MC, HC) FB1-contaminated corn for 3 weeks. The control diet contained uncontaminated corn only. Apoptotic kidney lesions of the type caused by FB1 were not found in the LC or MC groups. Lesions in the group fed HC were minimal and less severe than those found in the rats fed LU, MU or HU. Furthermore, significantly increased sphinganine and sphingosine concentrations indicative of FB1 exposure were found in the kidneys of the rats given LU, MU or HU. Concentrations were also elevated, but to a lesser extent, in rats fed HC, whereas sphinganine and sphingosine concentrations in rats given LC or MC did not differ from the control group. FB1 concentrations in the LC (0.08 mg kg−1), MC (0.13 mg kg−1) and HC (0.37 mg kg−1) diets were markedly reduced compared with their LU (1.8 mg kg−1), MU (3.5 mg kg−1) and HU (4.2 mg kg−1) counterparts as determined by HPLC (n = 1 analysis/diet). Taken together, the findings show that nixtamalisation is an effective cooking method for reducing the potential toxicity of FB1 contaminated corn.

Identification of systemic responses in soybean nodulation by xylem sap feeding and complete transcriptome sequencing reveal a novel component of the autoregulation pathway

Establishment of the nitrogen-fixing nodulation symbiosis between legumes and rhizobia requires plant-wide reprogramming to allow infection and development of nodules. Nodulation is regulated principally via a mechanism called autoregulation of nodulation (AON). AON is dependent on shoot and root factors and is maintained by the nodulation autoregulation receptor kinase (NARK) in soybean. We developed a bioassay to detect root-derived signalling molecules in xylem sap of soybean plants which may function in AON. The bioassay involves feeding of xylem extracts via the cut hypocotyl of soybean seedlings and monitoring of molecular markers of AON in the leaf. Transcript abundance changes occurring in the leaf in response to feeding were used to determine the biological activity of the extracts. To identify transcript abundance changes that occur during AON, which may also be used in the bioassay, we used an RNA-seq-based transcriptomics approach. We identified changes in the leaves of bioassay plants fed with xylem extracts derived from either Bradyrhizobium japonicum-inoculated or uninoculated plants. Differential expression responses were detected for genes involved in jasmonic acid metabolism, pathogenesis and receptor kinase signalling. We identified an inoculation- and NARK-dependent candidate gene (GmUFD1a) that responds in both the bioassay and intact, inoculated plants. GmUFD1a is a component of the ubiquitin-dependent protein degradation pathway and provides new insight into the molecular responses occurring during AON. It may now also be used in our feeding bioassay as a molecular marker to assist in identifying the factors contributing to the systemic regulation of nodulation.

Differential Feeding of Fall Armyworm Lepidoptera(Lepidoptera: Noctuidae) Host Strains on Meridic and Natural Diets

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is composed of two sympatric, morphologically identical host strains (corn and rice) that differ in their distribution on different host plants. This suggests possible strain specificity in the use of host plants. However, although feeding studies published since 1987 have reported such developmental differences, the results were often contradictory, making generalizations about strain-specific physiological traits problematic. Here, we tested whether more consistent results could be obtained using several genetically characterized colonies when assayed in the same laboratory. We also assessed whether a commonly used meridic diet was more favorable to one strain and the potential this might have on altering the behavior of artificially raised colonies. Corn and rice strain colonies were characterized by cytochrome oxidase I (COI) strain markers and were subjected to feeding studies using corn (Zea mays L.), stargrass (Cynodon nlemfuensis Vanderyst variety nlemfuensis ‘Florona’), and a meridic pinto bean diet. In 2005 bioassays, all colonies developed best on corn, whereas the meridic and stargrass diets were associated with more pronounced strain differences. However, bioassays conducted in 2010 using different colonies showed fewer differences between host strains. The limitations of feeding bioassays and the COI marker to identify host strains and the potential for unintended selection of corn strain traits when using a meridic diet are discussed.

Susceptibility to the Cry1F Toxin of Field Populations of Sesamia nonagrioides (Lepidoptera: Noctuidae) in Mediterranean Maize Cultivation Regions

Maize hybrids expressing the Cry1F toxin provide efficient control of lepidopteran pests. The Mediterranean corn borer, Sesamia nonagrioides (Lefèvre), is one of the most damaging pests of maize in the Mediterranean basin. In this work we firstly determined the efficacy of maize hybrids expressing the Cry1F toxin (event TC1507) to control neonates of S. nonagrioides. Leaf tissue feeding bioassays revealed that TC1507 maize is highly effective against this pest, and the percentage mortality obtained was comparable to that obtained with a Cry1Ab-expressing maize hybrid (Compa CB, event 176), which is known to be highly efficacious against S. nonagrioides. Secondly, interpopulation variation in the susceptibility to the Cry1F insecticidal protein was established for nine field-collected populations of S. nonagrioides (three Spanish, two French, two Italian, one Greek, and one Turkish). Estimates of the susceptibility of larvae to the Cry1F toxin showed low variability in lethal concentrations and growth inhibition concentrations among field populations. Moreover, no significant differences were found when they were grouped by geographical areas [Western Mediterranean (Spain and France) versus Eastern Mediterranean (Italy, Greece and Turkey)] or by history of exposure to Bt plants (Spanish vs. other populations). Therefore, the minor differences found in field populations can be attributed to natural variation in sensitivity to Cry1F. The importance of establishing baselines of susceptibility for resistance detection is discussed. Future changes in susceptibility of S. nonagrioides populations to Cry1F could be documented based on this baseline data.