Smart-use of fertilizers to manage spider mites (Acari: Tetrachynidae) and other arthropod pests

Fertilizers are utilized to increase productivity through improved crop growth and yield potential. However, steady declining availability of synthetic fertilizers is becoming a growing concern to the World’s food production industry. At the same time, there is increasing evidence that non-optimal (not applied at the right time and either at too high or too low dosages) applications of fertilizers may adversely affect the biochemical, physiological and morphological characteristics of crop plants, which in turn can adversely influence their resistance and/or increase their host suitability to pests. In this mini review, we discuss studies of spider mites (Acari: Tetranychidae) and their natural enemies to argue that, as part of a precision agriculture approach with temporally and spatially targeted applications, there is clear justification for more applied and basic research into smart-use of fertilizers as part of crop protection and research into “plant medicine”

Root-associated entomopathogenic fungi manipulate host plants to attract herbivorous insects

Root-associated entomopathogenic fungi (R-AEF) indirectly influence herbivorous insect performance. However, host plant-R-AEF interactions and R-AEF as biological control agents have been studied independently and without much attention to the potential synergy between these functional traits. In this study, we evaluated behavioral responses of cabbage root flies [Delia radicum L. (Diptera: Anthomyiidae)] to a host plant (white cabbage cabbage Brassica oleracea var. capitata f. alba cv. Castello L.) with and without the R-AEF Metarhizium brunneum (Petch). We performed experiments on leaf reflectance, phytohormonal composition and host plant location behavior (behavioral processes that contribute to locating and selecting an adequate host plant in the environment). Compared to control host plants, R-AEF inoculation caused, on one hand, a decrease in reflectance of host plant leaves in the near-infrared portion of the radiometric spectrum and, on the other, an increase in the production of jasmonic, (+)-7-iso-jasmonoyl-l-isoleucine and salicylic acid in certain parts of the host plant. Under both greenhouse and field settings, landing and oviposition by cabbage root fly females were positively affected by R-AEF inoculation of host plants. The fungal-induced change in leaf reflectance may have altered visual cues used by the cabbage root flies in their host plant selection. This is the first study providing evidence for the hypothesis that R-AEF manipulate the suitability of their host plant to attract herbivorous insects

Abiotic Factors Affecting Canola Establishment and Insect Pest Dynamics

Canola is grown mainly as an oil-seed crop, but recently the interest in canola has increased due to its potential as a biodiesel crop. The main objectives of this paper were to evaluate effects of abiotic factors and seed treatment on canola plant establishment and pest pressure in the Southern High Plains of Texas. Data was collected at two field locations during the first seven months of two field seasons. Based on multi-regression analysis, we demonstrated that precipitation was positively associated with ranked plant weight, daily minimum relative humidity and maximum temperature were negatively associated with plant weight, and that there may be specific optimal growth conditions regarding cumulative solar radiation and wind speed. The outlined multi-regression approach may be considered appropriate for ecological studies of canola establishment and pest communities elsewhere and therefore enable identification of suitable regions for successful canola production. We also demonstrated that aphids were about 35% more abundant on non-treated seeds than on treated seeds, but the sensitivity to seed treatment was only within four months after plant emergence. On the other hand, seed treatment had negligible effect on presence of thrips

Foraging on Individual Leaves by an Intracellular Feeding Insect Is Not Associated with Leaf Biomechanical Properties or Leaf Orientation

Nearly all herbivorous arthropods make foraging-decisions on individual leaves, yet systematic investigations of the adaptive significance and ecological factors structuring these decisions are rare with most attention given to chewing herbivores. This study investigated why an intracellular feeding herbivore, Western flower thrips (WFT) Frankliniella occidentalis Pergande, generally avoids feeding on the adaxial leaf surface of cotton cotyledons. WFT showed a significant aversion to adaxial-feeding even when excised-cotyledons were turned up-side (abaxial-side 'up'), suggesting that negative-phototaxis was not a primary cause of thrips foraging patterns. No-choice bioassays in which individual WFT females were confined to either the abaxial or adaxial leaf surface showed that 35% fewer offspring were produced when only adaxial feeding was allowed, which coincided with 32% less plant feeding on that surface. To test the hypothesis that leaf biomechanical properties inhibited thrips feeding on the adaxial surface, we used a penetrometer to measure two variables related to the 'toughness' of each leaf surface. Neither variable negatively co-varied with feeding. Thus, while avoiding the upper leaf surface was an adaptive foraging strategy, the proximate cause remains to be elucidated, but is likely due, in part, to certain leaf properties that inhibit feeding

Optimizing pesticide spray coverage using a novel web and smartphone tool, SnapCard

International audienceThe overuse of pesticides leads to contamination of water and food. Therefore, there is a need for tools and strategies to optimize pesticide application. Here we present SnapCard, a user-friendly and freely available decision support tool for farmers and agricultural consultants, available at snapcard.agric.wa.gov.au. SnapCard allows to predict, measure, and archive pesticide spray coverage quantified from water-sensitive spray cards. Variables include spray settings such as nozzle orifice size, sprayer speed, water carrier rate and adjuvant, and weather variables such as barometric pressure, relative humidity, temperature, and wind speed at ground level. We use separate regression models for four nozzles types. Our results showed that there are strong and positive correlations between water carrier rate and spray coverage for all four nozzle types. Moreover, sprayer speed is highly negatively correlated with obtained spray coverage. In addition, there is no consistent effect of either nozzle type or use of a particular adjuvant, across water carrier intervals. We conclude that varying combinations of spray settings and weather conditions caused marked ranges of spray coverages among the four nozzle types, thus highlighting the importance of selecting the right nozzle orifice size and type. We demonstrate that realistic scenarios of environmental conditions and spray settings can lead to predictions of very low spray coverage with at least one of the four nozzle types. We discuss how the novel and freely available smartphone app, SnapCard, can be used to optimize spray coverage, reduce spray drift, and minimize the risk of resistance development in target pest populations

The Search Behavior of Omnivorous Thrips Larvae is Influenced by Spider Mite Cues

The western flower thrips is an omnivorous insect that consumes both leaf tissue and spider mite eggs. For this reason, these thrips are often described as ‘opportunistic predators’ of spider mites. Several studies have shown that western flower thrips are often found in association with spider mites, and the development time of thrips decreases and their survivorship increases when they consume spider mite eggs. We tested the hypothesis that thrips larvae may respond to chemical cues from spider mites, and that they may modify their prey-searching behavior when these spider mite-induced cues are present. We prepared hexane extracts from: 1) webbing of spider mites isolated from maize leaves, 2) webbing produced by spider mites inside an empty glass tube to exclude any plant-derived cues from the extract, and 3) spider mite cuticle extracts. These three extracts were subsequently applied in droplets to one-half of filter papers, and hexane alone was applied in droplets to the other half. We showed that residence time of thrips larvae was higher on filter paper with spider mite webbing extract, especially when the extract originated from spider mites isolated in glass tubes. In the presence of webbing extracts, we also observed: 1) a decrease in velocity, 2) an increase of angular velocity and 3) an increase in time immobile. Extracts from spider mite cuticle only increased velocity and proportion of time immobile of the thrips larvae. Our results suggest that chemical cues from spider mite webbing induce an arrestment response and play an important role in the non-random search behavior of thrips larvae searching for eggs on spider mite infested plant leaves