Feeding behavior of a potential insect pest, Lygus hesperus, on four new industrial crops for the arid southwestern USA

Camelina (Camelina sativa), guayule (Parthenium argentatum), lesquerella (Physaria fendleri), and vernonia (Centrapalus pauciflorus [formerly Vernonia galamensis]) are either under limited commercial production or being developed for production in the southwestern USA. Insect pests are a potential economic threat to all these new crops, with Lygus hesperus, the western tarnished plant bug, among the most prominent due to its regional abundance and propensity to feed on reproductive plant tissue. The objectives of this study were to establish baseline data on the feeding behavior and potential impact of L. hesperus on camelina, guayule, lesquerella and vernonia. Behavioral observations of adult females and males, and nymphs of this insect were made in the laboratory. Insects spent ≈35% of their time either probing (=tasting) or feeding on various reproductive and vegetative tissues of guayule, lesquerella or vernonia, but only 20% on camelina. When insects did probe and feed they preferred reproductive tissues, primarily flowers and siliques/achenes, and there were differences in these behaviors relative to crop but not generally to insect stage or sex. Insects probed and fed more on flower tissue of guayule and vernonia compared with camelina and lesquerella, and more on siliques of lesquerella compared with achenes of vernonia. When probing and feeding on vegetative tissue, there was generally a preference for stems compared with leaves in all crops except guayule. Results show that L. hesperus will readily feed on the economically important tissues of all crops, and although research has shown that this feeding did not consistently affect lesquerella yield, further work will be needed to determine if such feeding poses a risk to commercial production of camelina, guayule or vernonia.     

Genotype by environment interaction of seed and oil yield in vernonia (Vernonia galamensis variety ethiopica)

Vernonia (Vernonia galamensis variety ethiopica) is a potentially novel renewable source of natural epoxy oil. The objective of this study was to determine the genotype by environment interaction and to identify superior and stable genotypes of vernonia with high seed and oil yield. Field experiments were conducted during 2006, 2007 and 2008 at two localities namely, Gabaza and Syferkuil. Ten selected genotypes of vernonia were evaluated for seed yield, oil content and oil yield using the randomized complete block design with three replications. Significant interactions (P ≤ 0.05) were detected among genotype by location for seed yield, oil content, oil yield and genotype by year for seed and oil yield. Genotype Vge-18 had the highest seed yield ranging between 3095 and 3337 kg/ha followed by Vge-17 yielding 3006-3137 kg/ha at Gabaza. These genotypes were also the best performers at Syferkuil where Vge-17 yielded 2915-3217 kg/ha followed by Vge-18 with 2819-3152 kg/ha. The superiority statistics allocated Vge-17 and Vge-18 as best yielding and stable genotypes. In both locations Vge-4 had increased seed oil contents at 43% (Gabaza) and 35% (Syferkuil). Other promising genotypes with high seed oil content were Vge-33 at Gabaza (40-43%) and Vge-3 at Syferkuil (34-35%). Genotypes with the highest oil yields were found to be Vge-18 (1117-1370 kg/ha) at Gabaza and Vge-4 with yields of 885-922 kg/ha at Syferkuil. Overall, Vge-17 and Vge-18 were identified as having the highest seed yield, while Vge-4 and Vge-3 yielded the highest seed oil content with average stability. These genotypes could be used for direct large scale production or strategic breeding of vernonia in these or similar environments.     

A methodology to assess the profitability of Bt-cotton: case study results from the state of Karnataka, India

Bt-cotton varieties can control lepidopterous pests, hence offering the possibility to reduce chemical pesticide use. India, with the largest cotton-growing area globally, gave commercial approval for Bt cotton in 2002 and a rapid adoption of the technology is expected. This paper uses a stochastic partial budgeting approach that captures the key pest control properties of Bt cotton taking into account uncertainty of pest pressure, control effectiveness and prices to assess the profitability effects of Bt varieties and hence complements previous studies that generally excluded such issues. Results of the simulation model reveal that under the current price situation a prophylactic chemical control strategy dominates the use of Bt varieties in both, irrigated and non-irrigated cotton. The effect of a higher cotton price is assessed in a second scenario that depicts a Bt cotton variety with improved fiber quality than varieties currently approved for commercial planting. Under this assumption, the Bt strategy would be slightly better than the prophylactic use of chemical pesticides. The model can be extended to include pests other than the bollworm and correlations among variables, e.g. prices and yield, provided sufficient evidence for such correlation exists. Results of this analysis show the impact of uncertainty in the main variables that influence the profitability of Bt cotton and alternative crop protection methods.     

Aggregation and Association of NDVI,Boll Injury,and Stink Bugs in North Carolina Cotton

Sampling of herbivorous stink bugs in southeastern U.S. cotton remains problematic. Remote sensing was explored to improve sampling of these pests and associated boll injury. Two adjacent 14.5-ha cotton fields were grid sampled in 2011 and 2012 by collecting stink bug adults and bolls every week during the third, fourth, and fifth weeks of bloom. Satellite remote sensing data were collected during the third week of bloom during both years, and normalized difference vegetation index (NDVI) values were calculated. Stink bugs were spatially aggregated on the third week of bloom in 2011. Boll injury from stink bugs was spatially aggregated during the fourth week of bloom in 2012. The NDVI values were aggregated during both years. There was a positive association and correlation between stink bug numbers and NDVI values, as well as injured bolls and NDVI values, during the third week of bloom in 2011. During the third week of bloom in 2012, NDVI values were negatively correlated with stink bug numbers. During the fourth week of bloom in 2011, stink bug numbers and boll injury were both positively associated and correlated with NDVI values. During the fourth week of bloom in 2012, stink bugs were negatively correlated with NDVI values, and boll injury was negatively associated and correlated with NDVI values. This study suggests the potential of remote sensing as a tool to assist with sampling stink bugs in cotton, although more research is needed using NDVI and other plant measurements to predict stink bug injury.     

Threshold-based interventions for cotton pest control in West Africa: What's up 10 years later?

In the late 1980s, after a long period during which insecticides were sprayed at preset dates to control cotton (Gossypium hirsutum L.) pests and their damage, some French-speaking countries in sub-Saharan areas decided to disseminate a special form of crop protection approach among smallholders, i.e. targeted staggered control (LEC, for Lutte étagée ciblée). According to this approach, decisions on some insecticide applications were made on the basis of infestation levels or the extent of crop injury caused by major pests: Aphis gossypii Glover aphids, Haritalodes (=Syllepte) derogata F., leaf-eating caterpillars, and more generally Helicoverpa armigera (Hübner), Diparopsis watersi Rothschild, Earias insulana (Boisduval) and Earias biplaga (Walker) bollworms. Polyphagotarsonemus latus (Banks) mites were sometimes included on this list. Today, the calendar-based or conventional program is still widely implemented with some changes in insecticides applied due to the development of pyrethroid resistance in H. armigera. Depending on the country, protection programs based on pest monitoring have been preserved or replaced by programs still using thresholds (staggered or true). In Benin, there are two forms of LEC tailored to two regions delineated according to the extent of damage caused by of bollworms that live inside cotton bolls, i.e. Thaumatotibia (=Cryptophlebia) leucotreta (Meyrick). The logical follow-up to LEC, involving true thresholds, was developed in Mali, Cameroon and, recently, Senegal. Cameroon opted for a sequential plan for individual decision program or LOIC (for Lutte après observation individuelle des chenilles), based on control after sequential sampling of bollworms. A calendar program with additional applications of insecticides based on a particular scouting of H. armigera was developed in Togo. In Ivory Coast, the use of true thresholds is limited to the beginning of the cotton crop cycle whereas in Burkina Faso true thresholds are used after the first two calendar sprayings. The present article describes the diversity of these cotton protection programs, sampling methods and associated intervention thresholds based on pests or injury levels in addition to the advantages and constraints associated with their adoption.     

Influence of the Color,Shape, and Size of the Clay Model on Arthropod Interactions in Turfgrass

Many predatory arthropods occur naturally in turfgrass, and they provide adequate control of lepidopteran pests, such as fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), and black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae). Recording predation is challenging under field conditions because predators rarely leave any evidence. Clay models were successfully employed for studying predation, and this technique is underutilized in turfgrass. Little is known about whether the characteristics of clay models, such as color, shape, and size, influence arthropod interactions in turfgrass. To improve the utility of clay models in turfgrass, the influence of the color, shape, and size of clay models on arthropod interactions was studied by exposing clay models during daytime and nighttime in a turfgrass field. The results showed that arthropods interacted with clay models, and various types of impressions were recorded, including paired marks, scratches, cuts, and pricks. Although the color of the clay model had no significant effects on arthropod interactions during the night, significantly greater numbers of impressions were noticed on the blue and green models than on the yellow models during the daytime. The caterpillar-shaped models captured significantly greater densities of impressions than the beetle-shaped models. Additionally, the number of impressions significantly increased with an increase in the size of the model regardless of shape.     

Impact of area-wide malathion on predatory arthropods and secondary pests in cotton during boll weevil eradication in Texas

The boll weevil, Anthonomus grandis grandis, has been eradicated from much of the cotton producing region of the US and to-date eradication efforts continue in Texas. While providing long-term economic and environmental benefits, area-wide applications of malathion used by the eradication program have been implicated in the disruption of biological control of some cotton pests. This study evaluated the impact of the area-wide boll weevil eradication on abundance of predatory arthropods and key pests of cotton during four years in central Texas. Multiple applications of malathion ULV significantly reduced seasonal mean densities of spiders, predatory bugs (Orius spp. Pseudatomoscelis seriatus, Nabis spp., Geocoris spp.), Chrysopidae larvae and red imported fire ant, Solenopsis invicta, collected from the cotton canopy. In contrast, densities of beet armyworm, Spodoptera exigua, heliothine and other lepidopteron larvae, cotton aphid, Aphis gossypii, and adult and larval convergent lady beetle, Hippodamia convergens, often increased in cotton fields under boll weevil eradication. The density of total predators measured during the mid-season (period of blooming and early boll development) was significantly and negatively correlated with density of beet armyworm larvae during the late-season (boll maturation period). Results suggest that the community of predatory arthropods in the cotton canopy, rather than one or several key predators, is important in suppressing outbreaks of S. exigua and other lepidopteran pests in cotton. Furthermore, the potential to use densities of generalist predators in mid-season to anticipate late-season outbreaks of beet armyworm during boll weevil eradication is discussed.     

Spatial and Temporal Dynamics of Stink Bugs in Southeastern Farmscapes

A 3-yr study (2009–2011) was conducted to examine the spatial and temporal dynamics of stink bugs in three commercial farmscapes. Study locations were replicated in South Carolina and Georgia, in an agriculturally diverse region known as the southeastern coastal plain. Crops included wheat, Triticum aestivum (L.), corn, Zea mays (L.), soybean, Glycine max (L.), cotton, Gossypium hirsutum (L.), and peanut, Arachis hypogaea (L.). Farmscapes were sampled weekly using whole-plant examinations for corn, with all other crops sampled using sweep nets. The predominant pest species of phytophagous stink bugs were the brown stink bug, Euschistus servus (Say), the green stink bug, Chinavia hilaris (Say), and the southern green stink bug, Nezara viridula (L.). Chi-square tests indicated a departure from a normal distribution in 77% of analyses of the variance to mean ratio, with 37% of slopes of Taylor’s power law and 30% of coefficient β of Iwao’s patchiness regression significantly greater than one, indicating aggregated distributions. Spatial Analyses by Distance IndicEs (SADIE) indicated aggregated patterns of stink bugs in 18% of year-end totals and 42% of weekly counts, with 80% of adults and nymphs positively associated using the SADIE association tool. Maximum stink bug densities in each crop occurred when the plants were producing fruit. Stink bugs exhibited greater densities in crops adjacent to soybean in Barnwell and Lee Counties compared with crops adjacent to corn or fallow areas. The diversity of crops and relatively small size of fields in the Southeast leads to colonization of patches within a farmscape. The ecological and management implications of the spatial and temporal distribution of stink bugs within farmscapes are discussed.     

Irrigated cotton in the tropical dry season. II: Biomass accumulation,partitioning and RUE

Growing cotton during the tropical dry season avoids many insect pests endemic in the wet season. The impact of low mid-season radiation and night temperature that characterise the dry season, on the conversion of radiation to biomass (RUE) and the partitioning of this biomass were measured as these were largely unknown. Over three seasons, two Gossypium hirsutum (upland) cultivars and a Gossypium barbadense cultivar were sown from March to June at the Ord River (15.5°S), Western Australia. For the highest yielding March and April sowings, final biomass was similar to high yielding temperate grown cotton (∼30° latitude) and was generally greater than May or June sowings. However, biomass was accumulated differently: maximum growth rate was 6–12 g/m²/day for 78–134 days compared with 15–25 g/m²/day for 25–60 days reported for temperate grown cotton. RUE changed significantly with ontogeny, peaking between squaring and early flowering. The range in RUE of 1.2–2.0 g/MJ throughout the crop lifecycle for the upland cultivars was similar to temperate climates where biomass was corrected to a glucose equivalent. The RUE of 1.2–2.3 g/MJ measured over the lifecycle of G. barbadense cultivar was the first reported for this species. From first square to first flower the variation in RUE could be explained by a linear decline (p < 0.05) with temperature, which may limit vegetative biomass in May and June sowings and in cooler than average seasons for March and April sowings. Due to favourable temperatures and water supply, sowing in March would have the greatest risk of rank growth. It was concluded the low temperature and radiation during flowering and boll growth combined to reduce crop growth rate but high yields were achieved when the crop boll filling phase was extended. Management must be tailored to ensure a high proportion of boll growth (60–80%) can occur after vegetative growth has terminated.     

Irrigated cotton in the tropical dry season. I: Yield,its components and crop development

Growing cotton during the dry (winter) season avoids many insect pests endemic in the wet season (summer) and could permit the reintroduction of cotton to the semi-arid tropics in Australia. This research addressed the questions: (1) what yield is possible given the lower mid-season radiation and temperature of the dry season, (2) the prediction and management of crop development using a range of sowing months to assess whether cotton can be grown and picked within the dry season. Over three seasons two Gossypium hirsutum L. (upland) cultivars and one Gossypium barbadense L. cultivar were sown from March, to June at the Ord River (15.5°S) in Western Australia. For the upland cultivars, lint yields of 1900–2300 kg/ha for March and April sowings were at the high end of Australian and International benchmarks. High lint yields were linearly correlated with a greater proportion of bolls that were located on outer sites on fruiting branches than for high yielding crops in temperate climates (∼30°lat.). The change in boll position increased the length of the growing season which was also linearly correlated with yield. Future research needs to confirm if low minimum temperatures early in flowering caused the change in boll position and to measure the impact of extreme temperature seasons on yield and time to maturity. The lint yield of the G. barbadense cultivar was highest at a March sowing, at least 87% of the upland cultivars, which is comparable with temperate climates. The frequency of temperatures >35 °C and <11 °C affected time to squaring, requiring modification of existing development models derived in temperate climates. It was concluded sowing during March to April should achieve the dual objectives of high yields and avoidance of rain at maturity. The wide temperature range observed in these experiments improved the prediction of boll period from mean temperature; this function should be applicable outside the semi-arid tropics.     

A Molecular Approach for Detecting Stage-Specific Predation on Lygus hesperus (Hemiptera: Miridae)

A molecular gut analysis technique is described to identify predators of Lygus hesperus (Knight), a significant pest of many crops. The technique is unique because it can pinpoint which life stage of the pest was consumed. Sentinel egg masses designed to mimic the endophytic egg-laying behavior of L. hesperus were marked with rabbit serum, while third instar and adult L. hesperus were marked with chicken and rat sera, respectively. Then, the variously labeled L. hesperus life stages were introduced into field cages that enclosed the native arthropod population inhabiting an individual cotton plant. After a 6-h exposure period, the predator assemblage, including the introduced and native L. hesperus population, in each cage were counted and had their gut contents examined for the presence of the variously marked L. hesperus life stages by a suite of serum-specific enzyme-linked immunosorbent assays (ELISA). The whole-plant sampling scheme revealed that Geocoris punticpes (Say) and Geocoris pallens Stal (Hemiptera: Geocoridae) and members of the spider complex were the numerically dominant predator taxa in the cotton field. The gut content analyses also showed that these two taxa appeared to be the most prolific predators of the L. hesperus nymph stage. Other key findings include that Collops vittatus (Say) (Coleoptera: Melyridae) and Solenopsis xyloni McCook (Hymenoptera: Formicidae) appear to be adept at finding and feeding on the cryptic L. hesperus egg stage, and that L. hesperus, albeit at low frequencies, engaged in cannibalism. The methods described here could be adapted for studying life stage-specific feeding preferences for a wide variety of arthropod taxa.     

Population dynamics of arthropods associated with early-season tomato plants as influenced by soil surface microenvironment

Two field studies were conducted in the San Joaquin Valley (SJV) of California in order to describe the association of arthropods and possible virus diseases with the plant canopy of early-season, bush-trained, fresh-market tomato (Lycopersicon esculentum L. cv. Shady Lady) over three soil surface microenvironments. The experimental treatments were based on alterations to planting bed surfaces, as follow: 1) soil covered with silver metalized, light-reflective plastic mulch; 2) soil covered with biological mulch consisting of killed, chopped, cool-season cover crop residues [mixture of triticale (X Triticosecale Wittm.), rye (Secale cereale L. cv. Merced), and common vetch (Vicia sativa L.)]; or 3) bare soil (not covered) – the SJV standard tomato production practice. In both studies, the predominant arthropods encountered in all treatments were the aphid species Aphis craccivora Koch, Macrosiphum euphorbiae Thomas, and Myzus persicae Sulzer; the western flower thrips (Frankliniella occidentalis Pergande), and the false chinch bug (Nysius raphanus Howard). These are all considered to be pests of cultivated tomato plants. Spiders were the most prevalent arthropod predator group recovered from foliage samples. All monitored arthropods, except spiders, were most abundant in tomato plants grown over the conventional, bare soil surface, and least abundant (P < 0.05) in plants grown over the silver plastic mulch. Spider numbers were highest in plant foliage over the biological mulch. Other arthropods commonly found on tomato plants in the SJV, including leafhoppers, whiteflies, various caterpillars, and predaceous taxa, were not commonly nor consistently encountered. This was likely due to the early-season timeframe of these studies. Similarly, foliar virus disease symptoms, which were originally targeted for monitoring, were virtually nonexistent. The only arthropod pest species encountered which consistently caused economically important damage to tomato fruit was N. raphanus. In both experiments, tomato fruits grown over the reflective plastic mulch had significantly less (69.5% and 39.7%, respectively) damage due to this pest than those over bare soil. The biological mulch gave inconsistent, intermediate damage reductions. Results from these two field studies showed that reflective plastic bed mulch suppressed populations of a variety of tomato canopy-associated arthropod taxa in early-season plantings, as compared to conventional, bare-soil beds. The biological bed mulch results were more inconsistent, but gave indications that killed cover crop residues, as well as the light-reflective plastic, may be of value in integrated pest management programs for fresh-market tomato production.     

Rodent abundance,stone bund density and its effects on crop damage in the Tigray highlands,Ethiopia

In areas of subsistence agriculture, a variety of soil conservation methods have been implemented in the last few decades to improve crop yields, however these can have unintended consequences such as providing habitat for rodent pests. We studied rodent population dynamics and estimated crop damage in high and low stone bund density fields for four cropping seasons in Tigray highlands, northern Ethiopia. Stone bunds are physical structures for soil and water conservation, and potentially habitat for rodents. We used a general model to relate the proportion of crop damage to rodent abundance, stone bund density and crop stages. Generally, rodent abundance remained relatively low during the study period, except during the fourth quarter of the 2010 cropping season. We found a positive correlation between rodent abundance and crop damage, and significant variation in rodent abundance and crop damage between high and low stone bund density fields. Furthermore, crop damage also varied significantly between crop stages. We concluded that Mastomys awashensis (Lavrenchenko, Likhnova and Baskevich, 1998) and Arvicanthis dembeensis (Ruppel, 1842) were the two most important crop pests in Tigray highlands causing significant damage. Fields with high stone bund density (∼10 m average distance apart) harbor more rodents and endure a significantly higher proportion of crop damage compared to fields with lower stone bund density (∼15 m average distance apart). The fact that rodent abundances peaked during the reproductive stage of the crop and around harvest implies the need for management intervention before these crop stages are attained.     

Spatiotemporal Distribution of Chinavia hilaris (Hemiptera: Pentatomidae) in Peanut-Cotton Farmscapes

The green stink bug, Chinavia hilaris (Say) (Hemiptera: Pentatomidae), is a pest of cotton in the southeastern United States, but little is known concerning its spatiotemporal distribution in agricultural farmscapes. Therefore, spatiotemporal distribution of C. hilaris in farmscapes where cotton fields adjoined peanut was examined weekly. Spatial patterns of C. hilaris counts were analyzed using SADIE (Spatial Analysis by Distance Indices) methodology. Interpolated maps of C. hilaris density were used to visualize abundance and distribution of C. hilaris in crops. For the six peanut-cotton farmscapes studied, the frequency of C. hilaris in cotton (94.8%) was significantly higher than in peanut (5.2%), and nymphs were rarely detected in peanut, indicating that peanut was not a source of C. hilaris into cotton. Significantly, aggregated spatial distributions were detected in cotton. Maps of local clustering indices depicted patches of C. hilaris in cotton, mainly at field edges including the peanut-to-cotton interface. Black cherry (Prunus serotina Ehrh.) and elderberry (Sambucus nigra subsp. canadensis [L.] R. Bolli) grew in habitats adjacent to crops, C. hilaris were captured in pheromone-baited stink bug traps in these habitats, and in most instances, C. hilaris were observed feeding on black cherry and elderberry in these habitats before colonization of cotton. Spatial distribution of C. hilaris in these farmscapes revealed that C. hilaris colonized cotton field edges near these two noncrop hosts. Altogether, these findings suggest that black cherry and elderberry were sources of C. hilaris into cotton. Factors affecting the spatiotemporal dynamics of C. hilaris in peanut-cotton farmscapes are discussed.     

Spatiotemporal Distribution of Chinavia hilaris (Hemiptera: Pentatomidae) in Corn Farmscapes

The green stink bug, Chinavia hilaris (Say) (Hemiptera: Pentatomidae), is a pest of cotton in the southeastern United States but little is known concerning its spatiotemporal distribution in corn cropping systems. Therefore, the spatiotemporal distribution of C. hilaris in farmscapes, when corn was adjacent to cotton, peanut, or both, was examined weekly. The spatial patterns of C. hilaris counts were analyzed using Spatial Analysis by Distance Indices methodology. Interpolated maps of C. hilaris density were used to visualize abundance and distribution of C. hilaris in crops in corn–peanut–cotton farmscapes. This stink bug was detected in six of seven corn–cotton farmscapes, four of six corn–peanut farmscapes, and in both corn–peanut–cotton farmscapes. The frequency of C. hilaris in cotton (89.47%) was significantly higher than in peanut (7.02%) or corn (3.51%). This stink bug fed on noncrop hosts that grew in field borders adjacent to crops. The spatial distribution of C. hilaris in crops and the capture of C. hilaris adults and nymphs in pheromone-baited traps near noncrop hosts indicated that these hosts were sources of this stink bug dispersing into crops, primarily cotton. Significant aggregated spatial distributions were detected in cotton on some dates within corn–peanut–cotton farmscapes. Maps of local clustering indices depicted small patches of C. hilaris in cotton or cotton–sorghum at the peanut–cotton interface. Factors affecting the spatiotemporal dynamics of C. hilaris in corn farmscapes are discussed.     

Impact of oilseed rape crop management systems on the spatial distribution of Brassicogethes aeneus (Fabricius 1775): Implications for integrated pest management

The pollen beetle is one of the most important oilseed rape pests wherever the crop is grown. If no control measures are applied, it can cause a greater than 50% reduction in yield. The over-use of insecticides (especially pyrethroids) to control the pollen beetle has led to the development of resistance. Thus, alternative control strategies are required. A field trial with three experimental fields with different contributions of turnip rape as a trap crop was established during the growth season of 2013–2014. A grid of GPS points was established on each field. Pollen beetle abundance was recorded at each GPS point by beating into trays, and damage was assessed by dissection of buds from terminal racemes. Data analysis was performed by two-way analysis of variance and the appearance of pollen beetle adults was processed in a geographic information system (GIS). Statistically significant differences were found in terms of the density of the pollen beetle population between trap crop plants and oilseed rape plants. Control thresholds on each oilseed rape field were not exceeded, whereas the density of the pollen beetle population on trap crop plants was greater by up to 40 fold, regardless of the contribution of trap crop plants. The data indicate that support systems should use sampling strategies that incorporate spatial information to model crop loss more accurately and that there may be the potential for spatially targeted applications of insecticides to optimize the influence of natural enemies in oilseed rape.     

Transovarial Effect of Novaluron on Tribolium castaneum (Coleoptera: Tenebrionidae) After Termination of Direct Contact

The insect growth regulator novaluron (Rimon 10 EC, Makhteshim-Agan Ltd, Israel) is used against many field pests on corn, vegetables, orchards, forests, and cotton plantations. Previously, we studied various effects of novaluron on stored grain pests. Termination in Tribolium castaneum (Herbst) eggs hatching after treating adults with novaluron and following restoration after adult transfer to untreated media was observed. The objective of this study was to investigate the restoration of T. castaneum egg hatch following transfer of adults from treated media to untreated favorable and unfavorable media. The time needed for hatching restoration of 50% of eggs laid by adults transferred from novaluron (1 ppm) treated flour to untreated flour (RT₅₀) was 2.7 d. RT₅₀ for those transferred to untreated wheat grain was 4.1 d. RT₉₀ in flour was 3.6 d, in grain—6.1 d. Varieties of RTs in grain and in flour with nonoverlapping confidence intervals indicate that RTs were significantly different. Delay of eggs hatching restoration for adults transferred from treated flour to unfavorable media (Petri dishes with limited amount of flour, lying of eggs not detected) was observed. RT₅₀ in flour was 2.1 d and RT₉₀—3.1 d, while RT₅₀ in the unfavorable media was 3.4 d and RT₉₀ 6.5 d. Delayed effect of egg hatching restoration after adult transfer to unfavorable media provides evidence of the significant role of insect physiological state in novaluron excretion and (or) degradation by T. castaneum females.     

Seasonal occurrence of Laodelphax striatellus in Spain: Effect on the incidence of Maize rough dwarf virus

Maize rough dwarf virus (MRDV) has emerged as a major constraint to maize crop production in Spain. The seasonal abundance of planthopper-vectored MRDV was studied during two consecutive years in trials located within the area with the highest incidence of MRDV. Insect density was estimated once every 15 days during the maize growing season using sticky and suction traps. Laodelphax striatellus Fallén was the sole planthopper present in these maize trials and 52% of the captured hoppers contained MRDV. The population of L. striatellus showed two peaks during the season; one in June and the other in September. Adults of L. striatellus were captured from mid-May to the beginning of October and viruliferous insects were captured from 18th May to the beginning of September. Levels of the incidence of MRDV were correlated with the first detection of planthoppers (whether carrying the virus or not) in maize fields during the early development stages of the crop, but not with the planthopper abundance. The data obtained in this study support that early sowing of maize could contribute to reduce the incidence of MRDV in the northeast of Spain.     

黄板对茶园末代绿盲蝽种群动态及空间分布型的影响

该文研究了黄板对茶园绿盲蝽种群动态及空间分布型的影响。在绿盲蝽高发期,黄板处理对绿盲蝽的发生量有着很好的控制作用,与对照处理差异显著;应用几种聚集度指标的计算公式和1wao、Taylor的回归方程式,分析和测定结果表明在绿盲蝽高发期,黄板处理改变了绿盲蝽的空间分布型,为均匀分布,对照处理为聚集分布。