B. R. Wiseman

Biochemical activity of centipedegrass against fall armyworm larvae

Centipedegrass,Eremochloa ophiuroides (Munro) Hack, severely inhibits growth of the fall armyworm larva,Spodoptera frugiperda (J.E. Smith). Fresh centipedegrass extracts and extract fractions were deposited on Celufil, incorporated into meridic-based diets and bioassayed against neonate larvae of the fall armyworm in the laboratory. The methanol extract (F1) caused the greatest reduction in larval weight. When F1, was partitioned between méthylene chloride and water, the activity was transferred to the water-soluble fraction (F5), which, when further fractionated using preparative C-18 reverse-phase chromatography, yielded active F7 and F8 fractions. Gas chromatograph-mass spectrometry and high-pressure liquid chromatography (HPLC) showed F7 to be 95% caffeoylquinic acids with chlorogenic acid as the major constituent. HPLC analysis of F8 revealed maysin [2″-O- α-L-rhamnosyl-6-C-(6-deoxy-Xylo-hexos-4-ulosyl)luteolin] and other luteolin derivatives. Chlorogenic acid and other caffeoylquinic acids, maysin, and other luteolin derivatives are the major factors responsible for the antibiotic resistance of centipedegrass to larvae of the fall armyworm.

Types and mechanisms of host plant resistance to insect attack

A keen appreciation of the types and mechanisms of resistance must be attained in order to fully understand and utilize resistant cultivars as effective tools in today’s pest management schemes. A historical account of plant resistance terminology is presented. Resistance can be classified as to intensities: immunity; high, moderate and low resistance; or types of resistance: vertical or horizontal resistance. The mechanisms of resistance include: non-preference, antibiosis and tolerance. Examples of the effects of both non-preference and antibiosis resistance on insect numbers are given.RésuméUne bonne appréciation des types et mécanismes de résistance doit être atteinte afin de comprendre entièrement et utiliser les cultivars résistants comme outils efficaces dans les systèmes actuels de lutte contre les pestes. Une historique de la terminologie de la résistance des plantes est présentée. La résistance peut être classifiée en intensities: immunité; grande résistance, résistance modérée, faible résistance; ou en types de résistance: résistance verticale ou horizontale. Les mécanismes de résistance incluent: la non-préférence, les antibiotiques, et la tolérance. Des examples d’effets de résistance due â la non-préférence et aux antibiotiques sur les insectes sont donnés.

Quantitative utilization of selected grasses by fall armyworm larvae

Food utilization by larvae of the fall armyworm (Spodoptera frugiperda [J. E. Smith]) (Lepidoptera: Noctuidae), showed greater consumption of corn (Zea mays L.) than pinto bean diet, ‘Tifton 10’, or ‘Coastal’ bermudagrass (Cynodon dactylon [L.] Pers.). Transfer of larvae from diet to susceptible grasses such as corn, ‘Tifton 10’ or ‘Coastal’ produced differences in growth rates as a result of food consumption rates. Transfer of larvae from diet to resistant grasses such as ‘common’ centipedegrass (Eremochola ophiuroides [Munro] Hack) ‘Tifton 292’ bermudagrass, and zoysiagrass (Zoysia sp.) reduced larval growth as a result of low consumption rates and/or greater metabolic expenditures. Larvae initially fed ‘Tifton 10’, ‘Coastal’, or centipedegrass before feeding on corn grew significantly faster than when they fed continuously on corn.

FALL ARMYWORM: EXPRESSIONS OF ANTIBIOSIS IN SELECTED GRASSES

Selected grasses, ‘Coastal,’ ‘Tifton 10,’ and ‘Tifton 292’ bermudagrass, Cynodon dactylon (L.) Pers., ‘common centipedegrass,’ Eremochola ophiuroides (Munro) Hack, zoysiagrass, Zoysia sp., and corn, Zea mays L., were evaluated in the laboratory as hosts for the fall armyworm, Spodoptera frugiperda (J. E. Smith), in forced-feeding tests to delineate more clearly the expressions of antibiosis. Data were recorded at 5, 7, and 9 days on weights of larvae, days to pupation, weights of pupae, pupal duration and survival on the various host grasses. Corn was the most suitable host for development of fall armyworm larvae, followed by Tifton 10 and Coastal bermudagrass. Larval development was slower on common centipedegrass than on Coastal bermudagrass. Tifton 292 bermudagrass and zoysiagrass were unsuitable hosts because of nonpreference and antibiosis. Wing pad deformities in pupae and/or serious lessions in adult wings were observed when resistant grasses (e.g., centipedegrass and Tifton 292 bermudagrass) were ...

Resistance to fall armyworm in converted sorghums.

Field experiments were conducted in 1988 to evaluate newly converted sorghum, Sorghum bicolor (L.) Moench, germplasm for both whorl and panicle resistance to feeding by larvae of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). In the whorl-stage resistance study, over 20 and 30 of the entries were significantly more resistant to FAW feeding than the resistant check at 7 and 14 days after infestation, respectively. Significant differences also were found among the entries for the number of FAW larvae that established per panicle 4 days after infestation.

Mechanism of whorl feeding resistance to fall armyworm among converted sorghum accessions

Field studies were conducted in 1989 to evaluate selected converted sorghum (Sorghum bicolor [L.] Moench) accessions for resistance to whorl‐stage feeding by larvae of the fall armyworm (Spodoptera frugiperda J. E. Smith) and to determine the mechanism of resistance. The sorghum was infested in the whorl 26 days after planting (DAP) in experiment 1 and 33 DAP in experiment 2. In experiment 1, the plant accessions ‘IS7273C,’ ‘IS7444C,’ ‘IS12573C,’ ‘IS12678C,’ and ‘IS12679C’ were more resistant (rating < 3) to damage by S. frugiperda larvae than the resistant check CIMMYT (CM) 1821 (rating 6.2) at 14 days after infestation (DAI). These genotypes were also more resistant (ratings ≤ 4 at 7 DAI and < 3 at 14 DAI) than the resistant check CM1821 (ratings 5.6 at 7 DAI and 8 at 14 DAI) in experiment 2. The number of larvae that established/plant on IS7273C, IS7444C, IS12573C, or IS12679C was significantly less compared with establishment on the resistant check CM1821 at 14 DAI in experiment 1 and at 7 and 14 DAI in experiment 2. Resistance in IS7273C, IS7444C, IS12573C, and IS12679C was mainly due to their rapid rate of growth which induced a quick change in the plant morphology from the whorl‐ to the panicle‐stage and did not permit a sustained colonization of larvae. This new type of resistance could be referred to as ‘morphological non‐preference’ as apposed to chemical non‐preference where non‐preference is due to plant chemical factors. These genotypes had a significantly shorter cycle than the other sorghum genotypes. Host evasion, a type of pseudoresistance, was the basis for resistance in ‘IS7794C’ and ‘IS7947C’. Tolerance was the major mechanism of resistance in the resistant check CM 1821.

ADVANCEMENTS IN THE USE OF A LABORATORY BIOASSAY FOR BASIC HOST PLANT RESISTANCE STUDIES

Modifications were made in laboratory bioassays for resistance of plants to the fall armyworm, Spodoptera frugiperda (J. E. Smith). A bioassay using a 6-mm diameter X 2-cm section of a plastic soda straw filled with a diet mixture proved sufficient to bioassay differences between resistant centipedegrass and susceptible bermudagrass. Chemical solvents used to dissolve plant fractions may in themselves be toxic to test insects. Ethyl alcohol required ca. 5 h to evaporate, when incorporated into an insect diet, before it was nontoxic to the fall armyworm. The bioassay was readily adaptable for use in the search for antibiotic factors from exotic plant species.

Growth and development of two polyphagous lepidopterans fed high- and low-tannin sericea lespedeza.

The biological impact of consumption of sericea lespedeza (Lespedeza cuneata (Dumont) G. Don) genotypes varying in tannin content was examined for two generalist insect herbivores, Heliothis zea Boddie and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Foliage of high‐ and low‐tannin genotypes did not substantially affect the growth and development of either species when incorporated into meridic diet except at large concentrations where a diet containing high tannin genotypes reduced larval weight and delayed pupation of both species. Fresh foliage of sericea lespedeza with varying levels of tannin did not adversely affect larval growth and development of S. frugiperda. All genotypes were a poor host for H. zea in that most larvae died before pupation. Initial larval weight of H. zea was not consistently different between high‐ and low‐tannin genotypes. Except for one low‐tannin genotype having a greater efficiency of conversion of digested diet than the other genotypes, foliage tannin content had little effect on diet assimilation and utilization and larval developmental and consumption rates of stages 6 and 7 H. zea larvae. H. zea neonates also did not show a significant preference for any genotypes. Therefore, tannin content of sericea lespedeza had relatively little effect on the growth and development of these generalist insect defoliators which suggests that low‐tannin genotypes of sericea lespedeza will not be substantially more susceptible to defoliation by these species. The poor performance of H. zea on all L. cuneata genotypes suggests that the plant may contain factors other than tannin that inhibit the growth and development of this species or that sericea lespedeza lacks essential nutrients for proper development of H. zea.

Bioassay for Screening Plant Accessions for Resistance to Fall Armyworm (Lepidoptera: Noctuidae) Using Artificial Diets

Laboratory bioassays demonstrated that formulation of artificial insect diet influenced the expression of antibiosis to fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), in grain sorghum, Sorghum bicolor (L.) Moench. Larvae of FAW were reared on a diet formulated with pinto bean and a diet formulated with no pinto bean, both supplemented with dried milk stage florets of resistant and susceptible sorghum genotypes. The sorghum lines showed a significantly higher antibiosis to FAW when mixed in the diet formulated with no pinto bean than when mixed in the diet containing the bean. Larvae that were fed the no-bean diet supplemented with resistant sorghum genotypes weighed one-half to one-third less, required longer to pupate, and resulted in lighter pupae than larvae reared on mixtures containing the bean. The results obtained when the larvae were reared on the bean diet were significantly correlated (P = 0.0001, r > 0.80, n = 18) with those recorded when the no-bean diet was used for the FAW variabl...

Spodoptera frugiperda resistance in developing panicles of sorghum accessions

Experiments were conducted in 1989 to evaluate converted sorghum accessions for preflowering extended panicle and soft-dough stage panicle feeding resistance to fall armyworm, Spodoptera Frugiperda (J. E. Smith), by incorporating plant tissue into artificial insect diet. Spodoptera Frugiperda biological parameters measured were larval and pupal weights, mean duration of the larval stage, time to adult eclosion, survivorship, fecundity, net reproductive rate, intrinsic rate of increase, and relative fitness. The converted lines IS 2246C, IS 2403C, IS 2825C, IS 7007C, IS 8337C, IS 12592C, IS 12612C, IS 12657C, IS 12666C, and IS 12681C were more resistant to both preflowering and soft-dough stage panicle feeding by S. frugiperda than the resistant check NK Savanna 5. The genotypes IS 1340C, IS 2553C, IS 2569C, IS 6911C, IS 7498C, IS 12219C, IS 12617C, IS 12662C, and IS 12664C were more resistant than the resistant check to S. frugiperda feeding in the soft-dough stage, but not in the preflowering stage of panicle development. Plant antibiosis was the major mechanism of resistance in these lines at both stages of the panicle development.RésuméDes lignées naines de sorgho, Sorghum bicolor (L.) Moench ont été évaluées pour déterminer leur résistance à la chenille légionnaire, Spodoptera Frugiperda (J. E. Smith) durant la phase préfloraison et la phase patte douce de la panicule. La résistance a été étudiée en incorporant des échantillons de panicule des différentes lignées dans le diète de l’insecte. Les paramètres biologiquesde l’insecte qui ont été mesurés étaient le poids des larves, le poids des nymphes, la durée de la phase larvale, le temps d’apparition de l’adulte, le taux de survivance, la fécondité, le taux net de réproduction, le taux intrinsec d’accroissement et l’aptitude relative. Les lignées naines IS 2246C, IS 2403C, IS 282SC, IS 7007C, IS 8337C, IS 12592C, IS 12612C, IS 126S7C, IS 12666C et IS 12681C étaient plus résistantes à la chenille que le témoin résistant NK Savanna 5 durant la phase préfloraison aussi bien que la phase patte douce de la panicule. Les lignées IS 1340C, IS 2S53C, IS 2S69C, IS 6911C, IS 7498C, IS 12219C, IS 12617C, IS 12662C et IS 12664C étaient plus résistantes que le témoin résistant durant la phase patte douce de la panicule, mais pas durant la phase préfloraison. L’antibiose était le méchanisme majeur de la résistance chez ces lignées de sorgho aux deux phases de la panicule qui ont été testées.