SUMMARYFatty acid derivatives are of central importance for plant immunity against insect herbivores; however, major regulatory genes and the signals that modulate these defense metabolites are vastly understudied, especially in important agro-economic monocot species. Here we show that products and signals derived from a single Zea mays (maize) lipoxygenase (LOX), ZmLOX10, are critical for both direct and indirect defenses to herbivory. We provide genetic evidence that two 13-LOXs, ZmLOX10 and ZmLOX8, specialize in providing substrate for the green leaf volatile (GLV) and jasmonate (JA) biosynthesis pathways, respectively. Supporting the specialization of these LOX isoforms, LOX8 and LOX10 are localized to two distinct cellular compartments, indicating that the JA and GLV biosynthesis pathways are physically separated in maize. Reduced expression of JA biosynthesis genes and diminished levels of JA in lox10 mutants indicate that LOX10-derived signaling is required for LOX8-mediated JA. The possible role of GLVs in JA signaling is supported by their ability to partially restore wound-induced JA levels in lox10 mutants. The impaired ability of lox10 mutants to produce GLVs and JA led to dramatic reductions in herbivore-induced plant volatiles (HIPVs) and attractiveness to parasitoid wasps. Because LOX10 is under circadian rhythm regulation, this study provides a mechanistic link to the diurnal regulation of GLVs and HIPVs. GLV-, JA-and HIPV-deficient lox10 mutants display compromised resistance to insect feeding, both under laboratory and field conditions, which is strong evidence that LOX10-dependent metabolites confer immunity against insect attack. Hence, this comprehensive gene to agro-ecosystem study reveals the broad implications of a single LOX isoform in herbivore defense.

The psyllid Bactericera cockerelli (Sulc) (Hemiptera: Psyllidae) is the vector of a bacterial pathogen causing zebra chip (ZC) disease in potato, Solanum tuberosum L. (Solanaceae). Recently, ZC has become important to potato growers and the potato chipping industry in the southwestern United States, Mexico, Central America, and New Zealand. In the current study, we evaluated the knockdown effect of 12 insecticides against adult B. cockerelli, and we examined the effects of treating potato leaves: top side only, bottom side only, or both sides. Within 48 h of exposure, abamectin showed the highest and most consistent rate of adult B. cockerelli mortality and a dosage response to three dosages within labeled field rates. Choice tests conducted in petri dishes, involving untreated potato leaves and leaves treated with abamectin, revealed that abamectin did not affect host preference of adult B. cockerelli. A residual test under field conditions revealed that, although highly effective immediately after application, abamectin-effect was nonsignificantly different from control treatments 24 and 48 h after field application. Higher adult B. cockerelli mortality was recorded from potato plants treated with ground application compared with aerial 48 h after application. Our results indicated that abamectin has a high knockdown effect on adult B. cockerelli and that it can be used effectively in insecticide rotation programs against adult B. cockerelli and ZC control in potatoes.

Approximately US $1.3 billion is spent each year on insecticide applications in major row crops. Despite this significant economic importance, there are currently no widely established decision-support tools available to assess suitability of spray application conditions or of the predicted quality or performance of a given commercial insecticide applications. We conducted a field study, involving 14 commercial spray applications with either fixed wing airplane (N=8) or ground rig (N=6), and we used environmental variables as regression fits to obtained spray deposition (coverage in percentage). We showed that (1) ground rig applications provided higher spray deposition than aerial applications, (2) spray deposition was lowest in the bottom portion of the canopy, (3) increase in plant height reduced spray deposition, (4) wind speed increased spray deposition, and (5) higher ambient temperatures and dew point increased spray deposition. Potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), mortality increased asymptotically to approximately 60% in response to abamectin spray depositions exceeding around 20%, whereas mortality of psyllid adults reached an asymptotic response approximately 40% when lambda-cyhalothrin/thiamethoxam spray deposition exceeded 30%. A spray deposition support tool was developed (http://pilcc.tamu.edu/) that may be used to make decisions regarding (1) when is the best time of day to conduct spray applications and (2) selecting which insecticide to spray based on expected spray deposition. The main conclusion from this analysis is that optimization of insecticide spray deposition should be considered a fundamental pillar of successful integrated pest management programs to increase efficiency of sprays (and therefore reduce production costs) and to reduce risk of resistance development in target pest populations.

Uniform and controlled applications of insecticides constitute a fundamental aspect of applied research on performance of insecticides. We describe and evaluate a spraying device made from an artist airbrush and a soda bottle, the "bottle sprayer," which can be used to apply insecticide formulations both under laboratory and field conditions. Using the bottle sprayer in conjunction with quantitative behavioral analysis, it was shown that (1) miticides can significantly affect movement patterns and (2) it is possible to quantify mite repellency to miticides. The combination of controlled sprays to portions of trial arenas and quantification of behavioral responses by individual spider mites may be used to address a wide range of applied questions related to spider mite ecology. We used the bottle sprayer to apply water on water-sensitive cards and used simple image analysis techniques to correlate average reflectance per pixels (quadratic reflectance in blue color band) with water dose applied. Consequently, we were able to propose a method to quantify dose applied based on average color on water-sensitive cards. The spray card analysis based on data generated with the bottle sprayer was used to interpret spray card data obtained from spray applications in a commercial potato, Solanum tuberosum L., field and to discuss the possibility of developing quality control procedures for insecticide applications in field crops.

No abstract