I. Billy Annan

Discovery of cyantraniliprole, a potent and selective anthranilic diamide ryanodine receptor activator with cross-spectrum insecticidal activity

Anthranilic diamides are an exceptionally active class of insect control chemistry that selectively activates insect ryanodine receptors causing mortality from uncontrolled release of calcium ion stores in muscle cells. Work in this area led to the successful commercialization of chlorantraniliprole for control of Lepidoptera and other insect pests at very low application rates. In search of lower logP analogs with improved plant systemic properties, exploration of cyano-substituted anthranilic diamides culminated in the discovery of a second product candidate, cyantraniliprole, having excellent activity against a wide range of pests from multiple insect orders. Here we report on the chemistry, biology and structure-activity trends for a series of cyanoanthranilic diamides from which cyantraniliprole was selected for commercial development.

Use of Fluorescence, a Novel Technique to Determine Reduction in Bemisia tabaci (Hemiptera: Aleyrodidae) Nymph Feeding When Exposed to Benevia and Other Insecticides

ABSTRACT The sweet potato whitefly, Bemisia tabaci (Gennadius), is an economically important pest in the United States and other countries. Growers in many places rely on the use of insecticides to reduce populations of B. tabaci. However, insecticides may take a few days to cause B. tabaci mortality and some do not reduce feeding before death. Earlier reduction of feeding of whiteflies would decrease the physiological effects on plants, reduce the production of sooty mold and potentially reduce the transmission of viruses. Measuring the reduction in feeding after the exposure of B. tabaci to an insecticide has proven difficult. This series of laboratory experiments demonstrate the usefulness of fluorescence in determining B. tabaci feeding cessation. Fluorescein sodium salt is systemically transported in the xylem from the roots to the plant leaves and absorbed by B. tabaci nymphs feeding on these plants. Nymphs start fluorescing shortly after the cotton plant root system is submerged in the fluorescein sodium salt. Using this novel technique, the effect of three insecticides with different modes of action, cyantraniliprole, imidacloprid, and spirotetramat on B. tabaci was evaluated and compared to determine reduction in feeding. Results indicate that B. tabaci nymphs feeding on a plant treated with Benevia have a significant reduction of feeding when compared with nymphs feeding on plants treated with imidacloprid or spirotetramat. Both Benevia and spirotetramat caused significant nymphal mortality by 48 h after exposure. This novel technique will be useful to demonstrate the feeding cessation or reduction in feeding produced by different insecticides in several sucking insect groups.

An EPG Study of the Probing Behavior of Adult Bemisia tabaci Biotype Q (Hemiptera: Aleyrodidae) Following Exposure to Cyantraniliprole

ABSTRACT Cyantraniliprole is a novel insecticide for control of multiple chewing and sucking insect pest species including the sweetpotato whitefly Bemisia tabaci (Gennadius), which is one of the most important polyphagous pests in tropical, subtropical, and Mediterranean regions. This study aims to evaluate the effects of cyantraniliprole on the probing behavior of B. tabaci on tomato. Electrical penetration graph data indicated that on plants treated with cyantraniliprole (foliar application), adult whiteflies of the genetic variant Q2 were not able to reach the phloem and consequently did not perform the activities represented by E1 and E2 waveforms, i.e., phloem salivation (during which inoculation of geminiviruses occurs) and phloem sap ingestion (during which geminiviruses are acquired by the whiteflies), respectively. The complete failure of B. tabaci biotype Q adults to feed from the phloem of tomato plants treated with cyantraniliprole could be explained by rapid cessation of ingestion because of the mode of action of this insecticide. Overall, these findings indicated that cyantraniliprole might represent a useful new tool for producers to protect tomato plants from damage by B. tabaci.

Stylet Penetration Activities by Aphis craccivora (Homoptera: Aphididae) on Plants and Excised Plant Parts of Resistant and Susceptible Cultivars of Cowpea (Leguminosae)

Abstract Direct current electrical penetration graphs (DC-EPGs) were used to analyze the stylet penetration activities of cowpea aphid, Aphis craccivora Koch, on plants of aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cultivars of cowpea, Vigna unguiculata (L.) Walpers. Aphid stylet penetration on whole plants at seedling, flowering, and podding stages were studied in one experiment, and in another experiment excised leaves from seedling plants, excised flowers, and excised pods were tested. Electrical signals depicting the aphid stylet penetration activities on their host plants were amplified, recorded onto a paper chart recorder, and scored for specific waveform patterns. Compared with similar tissues of ICV-1, intact leaves and excised seedling foliage of ICV-12 plants caused severe disruption of aphid stylet penetration activities. This was manifested in frequent penetration attempts that were abruptly terminated or unsustained, and in shorter penetration times, signifying antixenosis resistance in ICV-12. There was reduced occurrence of E waveforms, which represent stylet activity in plant vascular tissues. Also, prior exposure of test aphids to plants of one cultivar did not significantly influence the expected stylet penetration activities on plants of the other cultivar. Overall, ICV-12 exhibited high levels of resistance against A. craccivora.

Movement of cyantraniliprole in plants after foliar applications and its impact on the control of sucking and chewing insects

BACKGROUND Given the physical properties of insecticides, there is often some movement of these compounds within crop plants following foliar application. In this context, movement of two formulations of cyantraniliprole, an anthranilic diamide, was characterized for translocation to new growth, distribution within a leaf and penetration through the leaf cuticle. RESULTS Upward movement of cyantraniliprole to new plant growth via the xylem was confirmed using (14) C-radiolabeled cyantraniliprole and from Helicoverpa zea mortality on tomato leaves that had not been directly treated. Within a leaf there was significant acropetal movement (base to apex) of cyantraniliprole, but no significant basipetal movement (apex to base). Translaminar movement, the ability of a compound to penetrate the leaf cuticle, was demonstrated in a variety of plants, both with and without the use of adjuvants, by treating only the adaxial surface of the leaf and measuring control of diamondback moth (Plutella xylostella), green peach aphid (Myzus persicae) and sweetpotato whitefly (Bemisia tabaci) exposed in clip cages to the untreated abaxial surface. CONCLUSION The plant mobility and plant protection of cyantraniliprole is discussed with implications for use in insect resistance management and integrated pest management programs.

Effects of treatments for electrical penetration graph recordings on behaviour and biology of Aphis craccivora (Aphididae)

Abstract. Two laboratory studies were conducted to investigate effects of treatments for direct “current electrical penetration graph (DC‐EPG) recordings or ‘tether effect’, on behaviour and reproductive performance of cowpea aphid Aphis craccivora Koch. The experiments constituted a control study in application of DC‐EPGs to analyse cowpea aphid feeding behaviour and host plant resistance mechanisms. Resistant (ICV‐12) and susceptible (ICV‐1) cultivars of cowpea Vigna unguiculata (L.) Walp were used. EPG treatments included two groups of aphids: tethered aphids that were exposed to DC electricity via an attachment of a thin, flexible gold wire on their dorsum using a droplet of adhesive silver paint, and ‘free’ (untethered) aphids with a dorsal spot of silver paint only. EPGs of the tethered aphids were recorded continuously for c.! h, whereas from the ‘free’ aphids recordings were done only for brief periods of 2–5 min, by temporarily contacting a gold wire to the spot of silver paint. Waveform signals generated from resistance fluctuations and electromotive forces, and representing aphid stylet penetration behaviour were recorded. A separate experiment was conducted to investigate effects of EPG treatments on aphid survivorship and population growth. Overall, EPG treatments did not significantly affect aphid stylet penetration behaviour or life‐table parameters. However, effects of crop cultivar on those characteristics were significant. Waveform E2, which denotes aphid ingestion in phloem sieve elements, and non‐penetration behaviour were important indicators of aphid resistance in ICV‐12. Also, apart from the number of aphid generations, other life‐table parameters were useful indicators of ICV‐12 resistance. Thus, DC‐EPGs provided a reliable technique for studying aphid stylet behaviour, and investigation of aphid resistance in cowpeas.

Influence of duration of infestation by cowpea aphid (Aphididae) on growth and yield of resistant and susceptible cowpeas

Abstract The influence of duration of infestation by cowpea aphid Aphis craccivora Koch on aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cultivars of cowpea Vigna unguiculata (L.) Walp, were compared to uninfested controls. Five apterous adult aphids of similar age were infested on seedling plants for five durations of infestation: 3, 7, 14, 21 and 28 days, respectively. Treatments were removed after stipulated durations and extended leaf heights of plants (cm), counts of aphids per plant and samples for final estimates of crop growth rate (g/dm 2 land surface area/day) and relative leaf area growth rate (dm 2 /dm 2 / day), were recorded. After harvest, the pods per plant and seeds per pod were recorded as plant yields. ANOVA indicated significant ( P ⩽ 0.05) interactions between cultivar and duration of infestation, and between treatment and durations, for plant yields. Extended leaf heights of ICV-1 plants were significantly reduced after 7 days duration. Aphid counts were significantly higher on ICV-1 than on ICV-12 for all durations of infestation. Compared to ICV-12 plants, pods produced by ICV-1 plants were significantly reduced at all durations, while seeds per pod were significantly reduced by infestations of 7 days or longer. Time-based action thresholds within which Aphis craccivora infestations significantly reduced the growth and yield of the susceptible ICV-1 cultivar were 7–14 days for crop growth in biomass accumulation and leaf expansion, and 3–7 days for economic yields and extended leaf heights.

Effects of infestation by cowpea aphid (Homoptera: Aphididae) on different growth stages of resistant and susceptible cowpea cultivars

Field studies were conducted to characterise the effects of infestations by adult and nymphal stages of cowpea aphid, Aphis craccivora Koch, on the growth and yield of cowpea, Vigna unguiculata (L.) Walp. Seedling, flowering, and podding stage plants of aphid-resistant (cv. ICV-12) and aphid-susceptible (cv. ICV-1) cowpea cultivars were used in the studies. Four treatments (consisting of infestations with adult and nymphal aphids, caged controls and uncaged controls) were administered on plants for 22 days post-treatment. Eight parameters of crop success were measured: extended leaf heights (ELH); plant mortality; incidence of sooty mould; incidence and abundance of natural enemy species; crop growth parameters (net assimilation rate, [NAR] in g/dm2/day, and crop growth rate [CGR] in g/dm2 land surface/day); and plant yields (seeds per pod, weight per seed). Data were analysed using analysis of variance (ANOVA), orthogonal contrasts and 95% confidence intervals (C.I.). There were no significant (P > 0.05) differences between adult and nymphal infestations or between caged and uncaged controls, so the respective sets of data were combined for comparisons of aphid infestations with control treatments. Infestations caused severe plant stunting and other growth deformities, drastic yield reductions, higher plant mortality, greater incidence of natural enemies and abundance of Cheilomenes spp. on cv. ICV-1 than on cv. ICV-12, and on infested and uninfested plants. Aphid infestations did not significantly affect the incidence of sooty mould on plants of cv. ICV-12 or cv. ICV-1.RésuméDes études furent menées sur terrain pour caractériser les effets des infestations des stades adults et nymphal de l’aphide du niébé, Aphis craccivora Koch, sur la croissance et le rendement du niébé, Vigna unguiculata (L.) Walp. Les plantes aux stades de plantule, de floraison et de gousse d’une variété résistante de niébé (cv. IC V-12) et une autre susceptible (cv. ICV-1) ont été utilisées dans cette étude. Quatre traitements (consistant à infester les aphides adultes, les nymphes, les témoins configés en cage et les témoins non encagés) ont été administrés sur des plantes 22 jours aprés traitement. Huit paramétres pour caractériser le développement réussi de la plante ont été mesurés: accroissement de la hauteur des feuilles; mortalité de plantes; incidence du dépôt de suie; incidence et abondance d’ennemis naturels; paramétres de croissance de la plante (taux net d’assimilation [TNA] en g/dm2/jr et taux de croissance de la plante [TCP] en g/ dm2/surface de terre/jr); et rendements de la plante (nombre de graines par gousse, poids par graine). Les données ont été analysées à l’aide de l’analyse de variance (ANOVA), suivie de contrastes orthogonaux pour 95% d’intervalle de confiance. Il n’y a pas eu de difference significative (P > 0.05) entre témoins en cage et ceux libres; par conséquent, les données ont été groupées ensemble pour comparer les infestations d ‘aphides avec les témoins. Les infestations ont causé un sévére rabougrissement de la plante et d’autres malformations de croissance, des réductions drastiques de rendement, une mortalité, une incidence d’ennemis naturels et une abondance de Cheilomenes spp. sur cv. ICV-1 plus éléves que sur cv. ICV-12 ainsi que sur des plantes infestées et non infestées. On en a conclu que les infestations des nymphes et adultes de l’aphide du niébé ont causé des effets adverses significatifs sur la performance du niébé et que les réactions de la plante ont varié en fonction des variétés et de différents stages de croissance au sein d’une même variété.

Pattern and rate of within-field dispersal and bionomics of the cowpea aphid, Aphis craccivora (Aphididae), on selected cowpea cultivars

Comparative field studies were conducted during the rainy and dry seasons at the Mbita Point Field Station of ICIPE in southwestern Kenya, to investigate the pattern and rate of dispersal of Aphis craccivora on aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cowpea cultivars in relation to key weather factors. The effects of the dispersal trends on crop performance and aphid population dynamics were analysed. Treatments consisted of initial aphid releases at the north, south, west, east and centre of test plots and uninfested controls maintained on plants for 22 days. Parameters recorded included: pattern (direction of spread of aphids) and rate (number of aphid-infested plants at a given time) in test plots; crop growth and yields and associated factors such as incidence of sooty mould and plant mortality, and aphid density and associated factors, including the incidence of natural enemy species, particularly coccinellids. Dispersal was fastest when releases were made in the west, north and centre of plots, and resulted in adverse effects on ICV-1 growth and yields. Infestations of ICV-12 did not significantly affect crop performance. There was an apparent direct, positive relationship between wind direction and pattern of spread of aphid infestations, but this pattern was more apparent during the rainy season, when wind speeds were higher, than during the dry season. The incidence of natural enemy species correlated with the spread of aphid infestations, while the abundance of coccinellids correlated with aphid density.RésuméDes essais comparatifs en champs on été conduits en saison sèche et en saison pluvieuse à la Station Expérimentale de l’ICIPE, à Mbita-Point (Sud-Ouest du Kenya). Ceux-ci avaient pour objet d’étudier, en fonction des facteurs climatiques principaux, le mode de répartition et les taux de dispersion du puceron Aphis craccivora chez cultivars de niébé, dont le premier (ICV-12) résistant et le second (ICV-1) sensible. Les effets du mode de dispersion sur la performance de la culture et la dynamique de populations du puceron étaient analysés. Les traitements consistaient en lâchers initiaux de pucerons dans les points cardinaux (nord, sud, ouest, est, centre) des parcelles expérimentales et témoins. Les pucerons étaient maintenus sur les plantes pour une durée de 22 jours. Les paramètres étudiés étaient la direction de dispersion du puceron et le taux d’infestation des plantes, à l’intérieur des parcelles sous essais et à un temps donné; la croissance des plantes et les rendements. En plus de ces paramètres, étaient étudiés des facteurs associés comme l’incidence de miellat et la dépérissement de la plante; la densité du puceron et les facteurs associés dont: l’incidence des ennemis naturels et plus particulièrement les coccinelles. La dispersion des pucerons était plus rapide quand les lâchers étaient effectués dans les parties ouest, nord ou centre des parcelles. De tels lâchers avaient des effets néfastes sur la croissance et les rendements du cultivar ICV-1. Les infestations du cultivar ICV-12 n’ont pas significativement affecté la performance de la culture. Il y avait une relation directe et positive entre la direction du vent et la dispersion des infestations du puceron. Bien encore, cette dispersion était plus apparente pendant la saison pluvieuse quand la vitesse du vent était plus grande, plutôt qu’en saison sèche. L’ incidence des ennemis naturels collérait avec la dispersion des infestations de pucerons tandis que 1’ abondance de coccinelles collérait avec la densité du puceron.