Is attract‐and‐kill technology potent against insecticide‐resistant Lepidoptera?

Attract-and-kill techniques, associating an attractant and a contact insecticide in a sticky formulation, are a new way of controlling Lepidopteran pests. Insecticide resistance may, however, limit the effectiveness and even the attractiveness of such formulations where resistance pleiotropic effects influence pheromone perception. We have tested this hypothesis on resistant codling moths Cydia pomonella (L) using a commercial formulation containing (E,E)-8,10-dodecadien-1-ol (codlemone), the major component of the sex pheromone, as an attractant and permethrin as toxicant. We first compared the attractiveness of codlemone in a wind tunnel and the contact toxicity of pyrethroids on males of one susceptible and of three strains selected for resistance to diflubenzuron, deltamethrin and azinphos-methyl. The dose-response relationships of males of susceptible and resistant strains to codlemone did not differ significantly. The deltamethrin-selected strain was the most resistant to pyrethroids, exhibiting 138-, 25- and 18-fold resistance ratios to deltamethrin, cypermethrin and permethrin, respectively. The efficiency of the attracticide formulation, applied successively on filter paper support, glass support and wood support, was estimated by recording the mortality delay of males after natural contact with the formulation in the wind tunnel. The deltamethrin- and diflubenzuron-resistant strains were significantly less affected than the susceptible strain by contact with the attracticide on the wooden support, exhibiting 58- and 2.3-fold greater LT50 ratios, respectively. Mortality of deltamethrin-resistant moths did not exceed 40% after 48 h. The LT50 value was significantly greater on filter paper support than on the two other supports. Surprisingly, the LT50 ratio of the deltamethrin-resistant strain was markedly higher on filter paper support (1021-fold), which was more absorbent, than on the glass support (31-fold). No sublethal effects in terms of pheromone response, mating or fecundity occurred in moths surviving contact with the attracticide. Choice of insecticides in attracticide formulations will be influenced by the resistance background of the target pests. Principles of insecticide resistance management may also be applied to attract-and-kill technology by alternating with other insecticides or control methods.     

Can the parasitic weeds Striga asiatica and Rhamphicarpa fistulosa co‐occur in rain‐fed rice?

Striga asiatica and Rhamphicarpa fistulosa are important parasitic weeds of rain‐fed rice, partly distributed in similar regions in sub‐Saharan Africa (SSA). It is not evident whether their ecologies are mutually exclusive or partially overlapping. In Kyela, a rice‐growing area in south Tanzania where both parasites are present, three transects of about 3 km each across the upland–lowland continuum were surveyed in June 2012 and 2013. A total of 36 fields were categorised according to their position on the upland–lowland continuum as High, Middle or Low and soil samples were taken. In each field, parasitic and non‐parasitic weed species were identified in three quadrats. Additionally, in two pot experiments with four different moisture levels ranging from wilting point to saturation, influence of soil moisture on emergence and growth of parasites was investigated. Striga asiatica was observed in higher lying drier fields, while R. fistulosa was observed in the lower lying wetter fields. Furthermore, non‐parasitic weed species that were exclusive to S. asiatica‐infested fields are adapted to open well‐drained soils, while species that were exclusive to R. fistulosa fields are typical for wet soils. The experiments confirmed that S. asiatica is favoured by free‐draining soils and R. fistulosa by waterlogged soils. These results imply that changes in climate, specifically moisture regimes, will be crucial for future prevalence of these parasitic weeds. The non‐overlapping ecological range between their habitats suggests that their distribution and associated problems might remain separate. Thus, management strategies can be focused independently on either species.     

Are herbicide‐resistant crops the answer to controlling Cuscuta?

BACKGROUND: Herbicide‐resistant crop technology could provide new management strategies for the control of parasitic plants. Three herbicide‐resistant oilseed rape (Brassica napus L.) genotypes were used to examine the response of attached Cuscuta campestris Yuncker to glyphosate, imazamox and glufosinate. Cuscata campestris was allowed to establish on all oilseed rape genotypes before herbicides were applied. RESULTS: Unattached seedlings of C. campestris, C. subinclusa Durand & Hilg. and C. gronovii Willd. were resistant to imazamox and glyphosate and sensitive to glufosinate, indicating that resistance initially discovered in C. campestris is universal to all Cuscuta species. Glufosinate applied to C. campestris attached to glufosinate‐resistant oilseed rape had little impact on the parasite, while imazamox completely inhibited C. campestris growth on the imidazolinone‐resistant host. The growth of C. campestris on glyphosate‐resistant host was initially inhibited by glyphosate, but the parasite recovered and resumed growth within 3–4 weeks. CONCLUSION: The ability of C. campestris to recover was related to the quality of interaction between the host and parasite and to the resistance mechanism of the host. The parasite was less likely to recover when it had low compatibility with the host, indicating that parasite‐resistant crops coupled with herbicide resistance could be highly effective in controlling Cuscuta. Published 2009 by John Wiley & Sons, Ltd.     

Is the current state of the art of weed monitoring suitable for site‐specific weed management in arable crops?

Weed monitoring is the first step in any site‐specific weed management programme. A relatively large variety of platforms, cameras, sensors and image analysis procedures are available to detect and map weed presence/abundance at various times and spatial scales. Remote sensing from satellites or aircraft can provide accurate weed maps when the images are obtained at late weed phenological stages. Cameras located on unmanned aerial vehicles (UAVs) have been shown to be adequate for early‐season weed detection in a variety of wide‐row crops, providing images with relatively high spatial resolutions. Alternatively, weed detection/mapping systems from ground‐based platforms can achieve even higher resolutions using a variety of non‐imaging and imaging technologies. These ground systems are suited, in some cases, for real‐time site‐specific weed management. Despite this rich arsenal of technologies, their commercial adoption is, apparently, low. In this study, we describe the state of the art of remotely sensed and ground‐based weed monitoring in arable crops and the current level of adoption of these technologies, exploring major constraints for adoption and trying to identify research gaps and bottlenecks.     

Can a chitin‐synthesis‐inhibiting turfgrass fungicide enhance black cutworm susceptibility to a baculovirus?

BACKGROUND: Developmental resistance, i.e. reduced virulence and speed of kill of late instars, is a limiting factor in the use of baculoviruses for caterpillar control. Agrotis ipsilon multicapsid nucleopolyhedrovirus (AgipMNPV) is highly infective to young black cutworms, Agrotis ipsilon, but too slow‐acting against late instars for effective curative control on golf courses or sports fields. Chitin‐synthesis‐inhibiting fungicides containing the active ingredient polyoxin‐d are used to control fungal diseases in turfgrass, and similar compounds have been shown in the laboratory to synergize baculoviruses by disrupting peritrophic membrane function. This study tested whether applying the virus together with such a fungicide can synergize AgipMNPV activity against A. ipsilon in turfgrass. RESULTS: The addition of a chitin synthesis inhibitor failed to increase AgipMNPV infectivity to A. ipsilon in the field. Rather, delayed and slightly reduced mortality from viral infection was seen when larvae fed on fungicide/virus‐treated grasses as opposed to virus‐only treatments. Choice tests revealed the fungicide residues to be a mild feeding deterrent. CONCLUSION: Because polyoxin‐d does not deactivate AgipMNPV, the two substances are compatible. However, combination applications of polyoxin‐d and Agip MNPV on turfgrass might interfere with larval ingestion of a lethal virus dose, resulting in prolonged larval feeding in the field. Copyright © 2011 Society of Chemical Industry     

Does Fusarium‐caused seed mortality contribute to Bromus tectorum stand failure in the Great Basin?

Bromus tectorum (cheatgrass, downy brome) is an important invader in western North America, dominating millions of hectares of former semi‐arid shrubland. Stand failure or ‘die‐off’ is relatively common in monocultures of this annual grass. The study reported here investigated whether soil‐borne pathogens could be causal agents in die‐offs. Soils from two die‐off areas and adjacent B. tectorum stands were used in a glasshouse experiment with sterilised and non‐sterilised treatments. Soil sterilisation did not increase emergence, which averaged 80% in both die‐off and non‐die‐off soils. Seedling biomass was higher in die‐off soils, probably due to increased nitrogen availability. Fusarium was isolated from 80% of killed seeds in non‐sterilised soil treatments. In pathogenicity tests with 16 Fusarium isolates, host seeds incubated under water stress (?1.5MPa for 1 week prior to transfer to free water) suffered over twice the mortality of seeds incubated directly in free water (25–83% with water stress vs. 5–43% without water stress). These results suggest that soil‐borne Fusarium could play a role in B. tectorum stand failure in the field, but that low water stress conditions in the glasshouse experiment were not conducive to high levels of disease. Pathogenic Fusarium isolates were obtained from seeds planted in both die‐off and non‐die‐off soils, suggesting that microenvironmental factors that affect levels of water stress might be as important as relative abundance of soil‐borne pathogens in mediating spatial patterns of disease incidence in the field.     

Virulence structure of the <Emphasis Type="Italic">Blumeria graminis</Emphasis> DC.f. sp. <Emphasis Type="Italic">avenae</Emphasis> populations occurring in Poland across 2010–2013

The aim of the present study was to determine the virulence structure of powdery mildew of oats (Blumeria graminis DC.f. sp. avena) in Poland in the years 2010–2013. For this purpose, powdery mildew isolates were collected from three experimental stations in Poland. To assess the virulence of the isolates, eight oat varieties with different responses to the pathogen were used. The results showed that a significant proportion of powdery mildew isolates found in Poland overcame the resistance genes of varieties Bruno (Pm6), Jumbo (Pm1) and Mostyn (Pm3). In contrast, lines Av1860 (Pm4), Am27 (Pm5) and Cc3678 (Pm2) were completely resistant to all pathogen isolates involved in the experiment. Changes constantly occurring in the powdery mildew population perfectly reflect diversity indexes, which were the smallest in the first year of observation, where in the following years these parameters were significantly higher. It is worth noting that the presence of powdery mildew is seasonal and local, which is reflected in the prevalence of the disease in a defined area of the country.     

Are road verges corridors for weed invasion? Insights from the fine‐scale spatial genetic structure of Raphanus raphanistrum

Raphanus raphanistrum (Brassicaceae) is considered amongst the world's worst agricultural weeds. We address critical issues in its management by studying the pathway of colonisation at local scales. For this, we assessed the small‐scale spatial genetic structure of 231 samples collected from three different sites across the Cape Floristic Region, South Africa, using 11 nuclear microsatellite markers. Although natural pollen and seed dispersal were expected to be restricted, we found no significant relationship between genetic and geographical distance within sites. Instead, our results suggest that R. raphanistrum had colonised new habitats via jump dispersal, rather than through natural diffusive dispersal at local scales. We did not find evidence for road verges as dispersal corridors, as evidenced by a lack of isolation‐by‐distance at local scales. Instead, the absence of spatial genetic structure suggests that R. raphanistrum had rapidly spread throughout its current range, possibly facilitated by human‐mediated actions. Management plans addressing containment or suppression of the weedy species R. raphanistrum (and possibly other weedy species) should take the high degree of connectivity between distant geographical localities into account.     

Regulated non‐quarantine pests: fact or fiction?

A new category of officially regulated pests has been introduced during the past decade. The aim of this new categorization is to protect plant health and, in particular, farmers’ and growers’ crops against the introduction of pests via propagation material. The phytosanitary term ‘regulated non‐quarantine pests’ (RNQPs) is relatively new. It was introduced in 1997 as part of the new revised text of the International Plant Protection Convention. These RNQPs differ from the common category of quarantine pests in that they can be widespread within the territory of concern. Unlike quarantine pests, a level of tolerance could be applied for RNQPs infesting certain plants for planting. Some certification systems for the production of propagation material may specify certain tolerance levels, however, these systems are usually not regulated by national plant protection organizations and the tolerance levels are usually not based on scientific evidence. To date, only a few countries have applied the concept of RNQPs: notably Uruguay and Brazil. To apply the concept and, in particular, to determine specific tolerance levels presents many challenges. The concept may be embraced in the coming years by the European Community as part of the revision of the EU Council Directive 2000/29/EC.     

Transgenic citrus expressing the antimicrobial gene <Emphasis Type="Italic">Attacin E</Emphasis> (<Emphasis Type="Italic">attE</Emphasis>) reduces the susceptibility of ‘Duncan’ grapefruit to the citrus scab caused by <Emphasis Type="Italic">Elsinoë fawcettii</Emphasis>

Citrus scab, caused by Elsinoë fawcettii (anamorph Sphaceloma fawcettii), is a common foliar fungal disease affecting many citrus cultivars, including grapefruit. No commercial grapefruit cultivar is resistant to scab, and the disease results in severely blemished fruit which reduces its marketability. Transgenic ‘Duncan’ grapefruit trees expressing the antimicrobial attE gene were produced via Agrobacterium-mediated transformation. In in vitro leaf and greenhouse assays, several transgenic-lines had significantly lower susceptibility to E. fawcettii compared to the non-transformed control (P?P?P?attE mRNA was inversely related to the number of copies detected by Southern blot. The least susceptible line had a single inserted copy of the attE transgene whereas more susceptible lines had multiple copies. Since the attacin mode of action was thought to be specific to Gram-negative bacteria, it was unexpected to find that there was a significant activity against E. fawcettii.     

Sex-specific probing behaviour of the carrot psyllid <Emphasis Type="Italic">Bactericera trigonica</Emphasis> and its implication in the transmission of ‘<Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter solanacearum’

‘Candidatus Liberibacter solanacearum (Lso)’ is a pathogen of Solanaceae but also causes serious physiological disorders in carrots and celery (Apiaceae). In carrots, this pathogen is transmitted by the psyllids Bactericera trigonica and Trioza apicalis. How vector sex influences Lso transmission has not been yet elucidated. Here we report the probing behaviours of male and female B. trigonica and their impact on Lso titre transmitted, percentage of transmission, and symptoms produced on carrots when Lso is transmitted by males or females of B. trigonica. Vector sex affected the inoculation of Lso; our results suggest that females might inoculate higher Lso titres than males. However, the percentage of transmission was not affected by vector sex at a density of one or eight psyllids per plant. The number of yellow leaves and root weight were not different when Lso was transmitted by males or females at either of the psyllid densities tested, except for groups of females whose Lso transmission resulted in a higher number of yellow leaves than did Lso transmitted by groups of males. Electrical penetration graphs (EPG) showed that the proportion of individuals who reached phloem tissues was similar for males and females. However, EPGs also showed that females probed more times, ingested longer from phloem sieve elements and reached phloem tissues more frequently than did males during an 8-h inoculation access period (IAP). Our study shows that differences in probing behaviours between males and females of B. trigonica could modulate how Lso is inoculated by psyllids. These results highlight the importance of taking sex into consideration in psyllid studies of probing behaviour and bacterial transmission.     

Recombination-like sequences in the upstream region of the phage-type DNA polymerase in ‘<Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter asiaticus’

We determined and compared nucleotide sequences in the upstream region of the bacteriophage-type DNA polymerase in 15 Asian isolates of the citrus-greening bacterium ‘Candidatus Liberibacter asiaticus’ using the genomic information of American isolate Psy62. Some isolates had nucleotide changes and a large 156-bp deletion, which were concentrated in the putative bacteriophage genes ORF3 and ORF4 and corresponding intergenic region. Eight partial recombination-like patterns were observed in this variable region. Most were confirmed to have occurred between the original types 1 and 2, but a fragment, only several dozen nucleotides long and possibly derived from a third type, was also identified.     

Can rice genetic diversity reduce Echinochloa crus‐galli infestation?

Pot and field experiments were conducted to test whether rice genetic diversity can reduce Echinochloa crus-galli infestation through rice variety mixed-plantings. Two weed-suppressive rice ( Oryza sativa ) varieties, Guodao No. 1 (GD) and PI312777 (PI), and three non-suppressive varieties, Xiushui No. 63 (XS), Zhongjian No. 2 (ZJ) and Chunjiang No. 016 (CJ) were used. Monocultures (GD, PI, XS, ZJ and CJ), two-variety mixtures (GD + XS, GD + ZJ, GD + CJ, PI + XS, PI + ZJ, PI + CJ) and three-variety mixtures (GD + PI + XS, GD + PI + ZJ and GD + PI + CJ) were tested. Effects of herbicide on rice grain yield of non-suppressive varieties were compared between monocultures and mixtures. Pot experiment showed that E. crus-galli germination rate in all mixed-planting except CJ + PI, and E. crus-galli biomass in mixed-planting with GD decreased compared with monocultures. In a field experiment, E. crus-galli density decreased in all mixed-planting models of XS and CJ and ZJ + GD. Echinochloa crus-galli biomass reduction was found in XS + GD, XS + GD + PI, ZJ + GD and CJ + GD. Rice grain yield increased in XS + GD, ZJ + GD, CJ + GD, CJ + PI and CJ + GD + PI. Rice grain yields of non-suppressive varieties under mixtures without herbicides were lower than that in monoculture with full herbicide, but were not significantly different from monocultures with half rate herbicide. Moreover, rice yields of ZJ and CJ under mixtures with half rate herbicides did not decrease compared with monocultures with full rates. The results suggested that rice genetic diversity could reduce E. crus-galli infestation and herbicide utilisation through rice variety mixed-planting.