Monitoring resistance of Helicoverpa armigera to different insecticides used in cotton in Spain

Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD50's were estimated by probit analysis and resistance factors (RF) were calculated at the LD50 level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discusse

Population studies of arthropods on Melia azedarach in Seville (Spain), with special reference to Eutetranychus orientalis (Acari: Tetranychidae) and its natural enemies

Eutetranychus orientalis has become an important pest of the ornamental tree Melia 8 azedarach in the city of Seville (Spain). Trees suffer total defoliation at the end of summer. 9 Studies were conducted in a regular plantation of this tree in the Miraflores Park in 2008 and 10 2009, to determine the arthropod faunal composition, with particular interest in the possible 11 natural enemies of E. orientalis. Eutetranychus orientalis accounted for 98.3% of the 12 arthropods found on the leaflets. Two species of phytoseiids were found, Euseius scutalis and 13 Euseius stipulatus, but they only represented 0.2% of the arthropods. The most abundant 14 insect was the predator thrips Scolothrips longicornis, which accounted for 0.9% of the 15 arthropods found. The population of E. orientalis reached two peaks in 2008, with 325 16 individuals per leaflet in August, and 100 individuals per leaflet in November. Scolothrips 17 longicornis densities closely followed E. orientalis, and predation was observed on various 18 mite instars. Phytoseiids did not show such a response to the E. orientalis densities. 19 Eutetranychus orientalis was more abundant in the exterior part of the plantation. No 20 differences of arthropod densities were found between the various orientations in the 21 plantation (north vs. south, east vs. west), although E. orientalis densities were different 22 between rows. Distribution of E. orientalis population was highly aggregative, that of S. 23 longicornis population was less aggregative, whereas the phytoseiid population showed a 24 random distribution

Side effects of different pesticides used in citrus on the adult stage of the parasitoid Aphytis melinus DeBach (Hymenoptera Aphelinidae) and its progeny

Twelve pesticides commonly used in citrus in Spain were tested on adults of Aphytis melinus DeBach to determine their effects on parasitoid survival and fecundity, and the duration of the residue of each pesticide. Six of these pesticides were found to be harmless to moderately harmful to this parasitoid in a laboratory assay in closed Petri dishes: spinosad (bait formulation), azadirachtin, fenbutatin, fosetyl-Al, copper oxichloride, and mancozeb, with their scores on the reduction of beneficial capacity (RBC) index being between 21.4 and 94.6% after one week. The other six pesticides classified as harmful were tested on citrus plants to study their persistence over time under greenhouse conditions: Pirimicarb, pyriproxifen, paraffinic oil, abamectin, chlorpyrifos, and lambda-cyhalothrin. Most of these products reduced their negative effect on adults of A. melinus between one and six weeks after treatment, although lambdacyhalothrin was still harmful to parasitoids 11 weeks after application. This information can help growers and consultants to make decisions about pesticide selection and application timing in citrus in order to support IPM implementation when A. melinus is present

Effects of Bacillus thuringiensis Cry Toxins on Developmental and Reproductive Characteristics of the Predator Orius albidipennis (Hemiptera: Anthocoridae) Under Laboratory Conditions

The effects of Cry toxins from Bacillus thuringiensis (Berliner) (Bt) on the anthocorid Orius albidipennis Reuter were studied under laboratory conditions. Tritrophic experiments were performed, in which Orius nymphs were fed Helicoverpa armigera (Hu¨bner) larvae reared on a diet with Cry1Ac, Cry1Ab, or Cry2Ab toxins at different concentrations (0, 1, and 10 g/ml), when supplemented with Ephestia kuehniella Zeller eggs. In complementary experiments, the Bt Cry1Ac toxin was directly fed to Orius nymphs at a very high concentration (1 mg/ml). No effects on prey consumption, developmental time, nymph survival, fecundity, and egg hatching of O. albidipennis were found in either experiment. It can be concluded that the toxins tested do not seem to pose a risk for the anthocorid O. albidipennis, especially when it is exposed through the pre

Improving the knowledge of Aphytis melinus biology to optimize its mass production: influence of food source, host and parasitoid densities

The purpose of this work is to study the influence of several factors on fecundity and proportion of female parasitoids in the mass rearing of Aphytis melinus DeBach (Hymenoptera Aphelinidae). Its mass-rearing can be influenced by both host and parasitoid densities and by the available food source. In this study, host density did not influence the number of observed offspring per female per day (1.14 ± 0.15) or the sex ratio (0.32 ± 0.07 ♂) of A. melinus. Parasitoid density, on the other hand, did influence offspring production, with the higher parasitoid densities resulting in the lowest number of offspring (0.41 ± 0.07 per female per day). Medium and low parasitoid densities, meanwhile, produced similar numbers of offspring (0.83 ± 0.18 and 0.77 ± 0.13 per female per day, respectively). Sex ratio (0.43 ± 0.03 ♂) was not influenced by parasitoid density. The highest survival for A. melinus was achieved with honey (14.1 ± 1.2 days), but no statistical difference was observed with 10% honey. A mixture of honey, sugar and agar was not as good food source (only 3.0 ± 0.6 days of survival). Observed parasitoid host feeding was not continuous in the honey and 10% honey treatments, occurring only during 11.9 and 20.4% of the life-span, respectively. Maximum efficiency in offspring production per female was achieved when the host/parasitoid ratio was 5 to 10 hosts per female parasitoid per day. To maintain the lowest male bias of the offspring, female parasitoids should be in contact with the host for a period of no more than 3-4 days

Evaluation of the effect of different insecticides on the survival and capacity of 2 Eretmocerus mundus Mercet to control Bemisia tabaci (Gennadius) populations

Two different experiments were carried out to evaluate three insecticides. In the 24 first one, the effect of two insecticides, methomyl and indoxacarb, on pupae and 25 adults of the whitefly Bemisia tabaci (Gennadius) parasitoid Eretmocerus mundus 26 Mercet was evaluated under laboratory and greenhouse conditions, using sweet 27 pepper (Capsicum annuum L.) plants. In the second experiment, oxamyl was 28 tested to study its effect on the ability of E. mundus to parasitize and control B. 29 tabaci in sweet pepper plants, using a greenhouse cage evaluation. Methomyl and 30 indoxacarb caused low mortality of E. mundus pupae (17.6 and 7.8% 31 respectively), although methomyl mortality was significantly higher. Methomyl 32 produced 100% mortality on E. mundus adults with fresh and 24 hour-old 33 residues on leaves, significantly higher than the mortality produced by indoxacarb 34 (values ranged from 43.9 to 34.4%). The harmful effect of methomyl persisted for 35 a long time (up to 60 days). The results of the experiment with oxamyl showed 36 that E. mundus controlled whitefly population, without significant interaction 37 between the presence of the parasitoid and insecticide on whitefly mortality. 38 Whitefly mortality in the presence of the parasitoid was 87.8%, significantly higher 39 than the mortality in the absence of E. mundus (59.3%). Oxamyl did not produce 40 a significant effect on the emergence of E. mundus adults. Application of the 41 products in IPM programs is discussed

Toxicity of several d-endotoxins of Bacillus thuringiensis against Helicoverpa armigera (Lepidoptera: Noctuidae) from Spain

Toxicity and larval growth inhibition of eleven insecticidal proteins of Bacillus thuringiensis were evaluated against neonate larvae of Helicoverpa armigera, a major pest of important crops in Spain and other countries, by a whole-diet contamination method. The most active toxins were Cry1Ac4 and Cry2Aa1, with LC50 values of 3.5 and 6.3 μg/ml, respectively. At the concentrations tested, Cry1Ac4, Cry2Aa1, Cry9Ca, Cry1Fa1, Cry1Ab3, Cry2Ab2, Cry1Da, and Cry1Ja1, produced a significant growth inhibition, whereas Cry1Aa3, Cry1Ca2, and Cry1Ea had no effect

Effect of Biofumigation on Typical Weeds of Strawberry Fields

This research was conducted to evaluate the effect of biofumigation using fresh organic matter on typical weeds present in strawberry fields of southern Spain. Field experiments consisted of biofumigation (BF) treatment over 45 days, at two locations, with hen droppings or horse manure at a dose of 3 kg m-2, alone or in combination with solarization (BF+S) in an experimental randomized block design. Results showed good control of the main weed species, Poa annua, Portulaca oleracea and Lolium rigidum, with comparative populations of the three species under BF/BF+S of 42/4/8, 18/9/12, and 15/0/1 plants m-2 respectively. In addition, 20 seeds each of several weeds were sown inside cloth bags and were submitted to the treatment. The efficiency of biofumigation combined with solarization in the control of P. oleracea, Cynodon dactilon and Echinochloa crus-galli was 77/0, 50/15, and 30/2, as a percentage of germination of control/BF+S. Laboratory experiments consisted of simulating field conditions using a mix of soil, water and different fresh organic matter in a plastic bag, into which different seeds were sown and kept under controlled conditions over 30 days at 27ºC. Fresh organic matter used was whole strawberry plants, horse manure, hen droppings, and combinations of these. Best results were obtained with hen droppings, which showed effective control of Malva parviflora, Medicago sp., E. crus-galli, Amaranthus retroflesuxus, Chenopodium album and P. oleracea, while strawberry residues and horse manure were not useful as herbicides, sometimes even less so than the solarization treatment. Biofumigation with fresh hen droppings and solarization showed promising results in preliminary experiments

La transmisión de virus no persistentes estudiada a través del comportamiento de prueba de pulgones

Cinco años de investigación sobre el comportamiento de prueba del pulgón Myzus persicae Sulzer con la ayuda de un monitor electrónico de comportamiento (técnica EPG) han permitido obtener un mejor conocimiento sobre el mecanismo de transmisión no persistente de virus vegetales, empleando como modelo el virus Y de la patata (PVY). Las breves picaduras intracelulares producidas por el pulgón al inicio de la prueba son registradas en el monitor electrónico como breves caídas de potencial (denominadas pds). La presencia y morfología de este patrón de onda pd ha resultado ser clave en el proceso de tranmisión de PVY. Se ha observado que la presencia de al menos una pd es necesaria para la adquisición del virus, y que una mayor frecuencia de pds aumenta la probabilidad de adquisición. Asimismo, se ha comprobado que el proceso de inoculación del virus también tiene lugar durante la pd, más en concreto en su fase inicial III, mientras que la adquisición es un proceso posterior (fase 113). Esta evidencia pone en duda el mecanismo mayoritariamente aceptado de ingestión-egestión, proponiéndose como hipótesis alternativa un mecanismo de ingestión-salivación. Asimismo, la presencia y morfología de la fase 113 de la pd ha proporcionado una explicación satisfactoria al conocido efecto del ayuno previo (que aumenta la eficiencia de transmisión) y a la distinta capacidad vectorial observada en diferentes especies de pulgone