The nature of the effects of the aphids Sitobion avenae and Metopolophium dirhodum on the growth of wheat

Field-caged, post-anthesis populations of the aphids Sitobion avenae and Metopolophium dirhodum reduced grain weight of wheat by 14 and 7% respectively and induced changes in the senescence of the flag leaf. Spikelet number and grain number were unaffected as they are normally determined by pre-anthesis factors. Percentage grain protein was significantly reduced by both aphid species. The pattern of grain weight reduction within the ear was consistent with known limitations on the distribution of flag leaf assimilates among the grains. The relative effects of the two aphid species apparently resulted from the degree of nutrient drain imposed at particular feeding sites and the reduction in the leaf area duration of the flag leaf.     

Duration of cereal aphid populations and the effects on wheat yield and breadmaking quality

Field-caged and open-plot populations of the aphid Sitobion avenae on winter wheat (cv. Maris Widgeon) were sampled approximately twice-weekly in the summer of 1978. Cage populations began at growth stage 10.2 (Feekes scale) (Zadoks, G. S. 52); they were removed by spraying with pirimicarb at growth stages 10.54 (71), 11.1–11.2 (77) and 11.2–11.3 (85) respectively. All cage populations reduced mean weight per grain but the effect per aphid unit was lowest in the population of longest duration. Although the aphid index in the open plots was higher than that in the early cage treatment, yield was unaffected. Cage infestations affected the breadmaking quality of the grain: percentage flour extraction was reduced and there was an increase in colour, nicotinic acid content and thiamine (vitamin B₁) content of the flour; percentage nitrogen in the flour was unaffected but there was a reduction in baking value and in the high molecular weight glutenin content; infestation also reduced α-amylase activity. Different aspects of grain quality did not change in parallel with one another or with yield changes and thus damage thresholds will vary according to the yield/quality measure under consideration.     

Performance and prospects of Rag genes for management of soybean aphid

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an invasive insect pest of soybean [Glycine max (L.) Merr. (Fabaceae)] in North America, and it has led to extensive insecticide use in northern soybean‐growing regions there. Host plant resistance is one potential alternative strategy for managing soybean aphid. Several Rag genes that show antibiosis and antixenosis to soybean aphid have been recently identified in soybean, and field‐testing and commercial release of resistant soybean lines have followed. In this article, we review results of field tests with soybean lines containing Rag genes in North America, then present results from a coordinated regional test across several field sites in the north‐central USA, and finally discuss prospects for use of Rag genes to manage soybean aphids. Field tests conducted independently at multiple sites showed that soybean aphid populations peaked in late summer on lines with Rag1 or Rag2 and reached economically injurious levels on susceptible lines, whereas lines with a pyramid of Rag1 + Rag2 held soybean aphid populations below economic levels. In the regional test, aphid populations were generally suppressed by lines containing one of the Rag genes. Aphids reached putative economic levels on Rag1 lines for some site years, but yield loss was moderated, indicating that Rag1 may confer tolerance to soybean aphid in addition to antibiosis and antixenosis. Moreover, no yield penalty has been found for lines with Rag1, Rag2, or pyramids. Results suggest that use of aphid‐resistant soybean lines with Rag genes may be viable for managing soybean aphids. However, virulent biotypes of soybean aphid were identified before release of aphid‐resistant soybean, and thus a strategy for optimal deployment of aphid‐resistant soybean is needed to ensure sustainability of this technology.     

Suppressing spread of alfalfa mosaic virus in grazed legume pasture swards using insecticides and admixture with grass, and effects of insecticides on numbers of aphids and three other pasture pests

Field experiments were sown with alfalfa mosaic virus (AMV)‐infected or healthy seed of burr medic (Medicago polymorpha) and grazed by sheep. Seed‐infected plants acted as primary sources for virus spread by naturally occurring aphids. Admixture with annual ryegrass (Lolium rigidum), a non‐host of AMV, and different insecticides were used in attempts to suppress virus spread. Sowing swards to provide the ratios 1 : 4 and 1 : 13 of medic:ryegrass plants diminished AMV spread in medic plants by 23% and 45% respectively. Applications of organophosphorus (demeton‐s‐methyl), carbamate (pirimicarb) and newer generation synthetic pyrethroid (alpha‐cypermethrin) insecticides, all significantly decreased final AMV incidence. Alpha‐cypermethrin was the most effective, suppressing AMV incidence by 87% (two sprays), 79% (one late spray) and 65% (one early spray). Two sprays of demeton‐s‐methyl decreased incidence by only 36%, while two and 2 weekly applications of pirimicarb diminished it by 29–65% and 35–70% respectively. AMV infection of medic seed harvested decreased by up to 76% in sprayed plots. Insecticide treatment did not prevent winged aphids from landing but numbers of wingless Acyrthosiphon kondoi colonising swards were suppressed by up to 92% by spraying with pirimicarb and up to 96% by alpha‐cypermethrin. A. kondoi were much slower to recover with alpha‐cypermethrin than with pirimicarb, the former still significantly diminishing its numbers 35 days after spraying. Alpha‐cypermethrin was also very effective at suppressing Halotydeus destructor and Penthaleus major but not Sminthurus viridis. Greater effectiveness of insecticides in controlling spread of AMV in pasture than has been found previously with non‐persistently aphid‐transmitted viruses in annual crops seems due to the key role played by wingless aphids as virus vectors.     

Does the presence of grassy strips and landscape grain affect the spatial distribution of aphids and their carabid predators?

• 1 We investigated, over the course of 2 years, the spatial distribution and abundance of two species of aphid, Metopolophium dirhodum and Sitobion avenae, and predatory species of carabid. This was undertaken in 24 wheat fields in ‘coarse‐grain’ and ‘fine‐grain’ landscapes in western France. A greater percentage of the latter landscape was covered by hedgerows and grassland and the total area covered by fields and the average size of the fields were smaller.
• 2 The effects on aphid abundance of the distance from field margins, the presence of grassy strips and carabid abundance were determined in both landscapes.
• 3 Both aphid species were more abundant in the ‘fine‐grain’ landscape, which may have been a result of the higher density of semi‐natural elements. In both types of landscape, the total numbers of aphids were negatively correlated with the distance from the field margin. This may have been because aphids were dispersing from overwintering sites in field margins. The abundance of M. dirhodum was strongly negatively correlated with the presence of grassy strips in the ‘coarse‐grain’ landscape, although there were no such significant correlations for either of the aphid species in the ‘fine‐grain’ landscape.
• 4 Aphid and carabid abundances were negatively correlated in the ‘fine‐grain’ and positively in ‘coarse‐grain’ landscape.
• 5 The results obtained in the present study emphasize the importance of semi‐natural areas in agricultural landscapes in shaping the spatial distribution of aphids and carabid beetles, their natural enemies, at different spatial scales.

     

Glutathione S-transferase detoxification as a potential pyrethroid resistance mechanism in the maize weevil, Sitophilus zeamais

Insecticide resistance patterns among 16 Brazilian populations of the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), were recognized by surveying resistance to three organophosphates (chlorpyrifos‐methyl, malathion, and pirimiphos‐methyl) and three pyrethroids (cypermethrin, deltamethrin, and permethrin). Two population clusters were obtained: one with three populations (Bragança Paulista, Cristalina, and Nova Andradina) showing low frequency of cypermethrin resistance (13–36%) and negligible frequency of deltamethrin resistance (2–9%); and another with six populations (Campos dos Goytacazes, Ivinhema, Patos de Minas, Penápolis, Uberlândia, and Venda Nova) showing low to negligible levels of pyrethroid resistance (0–23%). The remaining seven populations, including a susceptible, and a DDT‐ and pyrethroid‐resistant reference populations (Sete Lagoas and Jacarezinho, respectively), were significantly different from each other and from the two recognized clusters. In contrast with pyrethroid resistance, organophosphate resistance was negligible except for chlorpyrifos‐methyl in two populations (Fátima do Sul and Penápolis). There was no correlation between geographic distance and the Mahalanobis distance estimated from the resistance pattern ordination of the populations by canonical variate analysis, suggesting local selection and/or broad dispersal of resistant populations by grain trade. The results of biochemical in vitro studies measuring the activity of detoxification enzymes (esterases and glutathion S‐transferases) in conjunction with canonical correlation analysis suggest a major involvement of enhanced conjugation by glutathione S‐transferases (> 2‐fold increase) in pyrethroid resistance and, in the case of cypermethrin resistance, enhanced phosphotriesterase activity.     

Seasonal changes of resistance to fenvalerate and cypermethrin in the larval parasitoid Cotesia plutellae （Hymenoptera： Braconidae）

The seasonal changes of insecticide resistance and stability in hymenopteran Cotesia plutellae, collected from Jianxin, Fuzhou-City, and Shangjie, Minhou-County, Fujian, China, were assessed by using a dry residual film method. The resistance to two insecticides in the field populations of C. plutellae was not stable under insecticide-free conditions in the insectarium. Compared with susceptible F11 progeny of C. plutellae in the insectarium, the resistance ratios （RR） in F0 parents were 18.4 for fenvalerate and 11.4 for cypermethrin based on LC50 at 9 hours, and 32.8 for fenvalerate and 28.5 for cypermethrin based on LC50 at 24 hours when the parasitoids were left in contact with the insecticides for 1 hour and mortalities were recorded at 9 and 24 hours, respectively. However, the RR in a field population of C. plutellae were 9.2 for fenvalerate and 12.7 for cypermethrin, if the parasitoids were left in contact with the insecticides for 24 hours. The resistances to the two pyrethroids in other field populations collected from Jianxin and Shangjie from November 2000 and July 2004 were also determined. Significant seasonal variations of resistance to the two insecticides in the field populations of C. plutellae were found. The RR were 3.0-18.4 for fenvalerate and 4.8-20.6 for cypermethrin in Jianxin populations from November 2000 to April 2002 based on LC50 at 9 h, and 2.3-13.6 for fenvalerate and 3.6-16.0 for cypermethrin in Shangjie populations from May 2002 to July 2004 based on LC50 at 24 hours. The resistance levels were high in spring and autumn and decreased sharply in summer. In addition, significant recovery from the knocked-down caused by the insecticides was found in the F0 and field populations of C. plutellae which were resistant to fenvalerate and cypermethrin if the parasitoids were left in contact with the pyrethroids for 1 hour. However, no recovery was found in susceptible F11 progeny.     

Introduced ants reduce interaction diversity in a multi‐species,ant–aphid mutualism

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence.     

The development of an action threshold for cabbage aphid (Brevicoryne brassicae) in oilseed rape in the UK

Replicated small plot field experiments were done at two sites growing winter oilseed rape (ADAS Boxworth, Cambridgeshire and ADAS High Mowthorpe, North Yorkshire) and two sites growing spring oilseed rape (ADAS Bridgets, Hampshire and ADAS Rosemaund, Herefordshire) to investigate the effect of cabbage aphid (Brevicoryne brassicae) on crop yield and quality. All four sites were included in the first 2 yr of the experiment in 1994 and 1995 but only those with winter oilseed rape were continued into the final year in 1996. Plots were artificially inoculated with cabbage aphids at either five aphid 4 m^-2 or 5 aphids 16 m^-2 or left uninoculated to become naturally infested. In 1995 and 1996 the naturally infested treatment was omitted. Sprays of the aphicide pirimicarb at GS 3.3, 3.7, 4.5, 4.9 and 5.5 were used to manipulate aphid populations. Once a plot had been treated at a target growth stage it was sprayed on all subsequent occasions to prevent recolonisation. Aphid numbers were assessed prior to each spray date and their effect on the crop measured in terms of yield of seed and oil and glucosinolate content. Artificial inoculation of aphids was often successful in establishing different populations of the pest at a range of growth stages. Results showed that cabbage aphid sometimes reduced both crop yield and quality. Yield responses to insecticide treatment tended to be larger in spring oilseed rape than in winter oilseed rape mainly because it became more heavily infested at an early growth stage. Tentative thresholds are proposed for control of the pest in both winter and spring oilseed rape. It is stressed that cabbage aphid is a sporadic pest and rarely likely to reach these threshold levels in field crops.     

Farm‐scale assessment of movement patterns and colonization dynamics of the grain aphid in arable crops and hedgerows

1 Integrated management of crop pests requires the identification of the appropriate spatial scale at which colonization processes occurs. We assessed, by coupling demographic and genetic methods, the relative contribution of local and transient migrants of the grain aphid Sitobion avenae to wheat field colonization in spring. 2 We examined, during two consecutive years, the daily colonization of wheat by aphid migrants and compared this with daily aphid flight monitored by a local 12.2‐m suction trap. The genetic profiles of aphids landing on crops were compared with those of both flying aphids caught by the suction trap and local populations from arable crops and hedgerows. 3 In the first year, we observed: (i) a strong correlation between aphids colonizing the crop and those moving within the crop and a close genetic similarity between aphids from these samples and (ii) a high level of genetic differentiation between these aphids and populations from local cereals and field margins. In the second year, the number of migrants recorded on the wheat was three‐fold higher than in the previous year, and less correlated with that recorded by the suction trap. This was associated with a lack of genetic differentiation between all samples. 4 This variation in the colonization processes resulted mainly in an abrupt increase in abundance of genotypes from local over‐wintering sites in 2004. This suggests that, despite the long range dispersal potential of the grain aphid, outbreak risks could be mainly determined at a local scale, encouraging the design of relatively small management units.     

Interactions between green spruce aphid (Elatobium abietinum (Walker)) and Norway and Sitka spruce under high and low nutrient conditions

1 Green spruce aphid (Elatobium abietinum) is a serious pest of spruce (Picea spp.) in north‐west Europe, causing defoliation of one‐year‐old and older needles. 2 Relationships between population development of E. abietinum, needle loss and tree growth were compared for five pure genotypes of Sitka spruce and mixed‐genotype material of Sitka and Norway spruce, grown under high and low nutrient conditions. 3 Despite wide differences in flushing date between spruce genotypes, E. abietinum populations peaked on the same date on each genotype and on the mixed‐genotype material, irrespective of nutrient supply. 4 Larger aphid populations developed on trees grown under high nutrient conditions than under low nutrients. However, more needles were lost per aphid in the low nutrient treatment and overall defoliation rates in the two nutrient treatments were similar. 5 Total aphid numbers differed significantly between Sitka spruce genotypes within nutrient treatments, but not in relation to bud‐burst or needle terpene content. Reductions in height growth caused by infestation were greater (15–44%), and related to mean aphid densities and defoliation, in the low nutrient treatment, but were smaller (11–27%) and not related to aphid density and defoliation in the high nutrient treatment. 6 Development of E. abietinum populations was similar on Norway and Sitka spruce, but Norway spruce lost fewer needles. However, the effects of infestation on tree growth were more closely related to aphid density and were similar for Norway and Sitka spruce. 7 Infestation caused a decrease in total root dry weight of Norway and Sitka spruce in proportion to the reductions observed in above‐ground growth.     

Abscisic acid deficiency increases defence responses against Myzus persicae in Arabidopsis

Comparison of Arabidopsis thaliana (Arabidopsis) gene expression induced by Myzus persicae (green peach aphid) feeding, aphid saliva infiltration and abscisic acid (ABA) treatment showed a significant positive correlation. In particular, ABA‐regulated genes are over‐represented among genes that are induced by M. persicae saliva infiltration into Arabidopsis leaves. This suggests that the induction of ABA‐related gene expression could be an important component of the Arabidopsis–aphid interaction. Consistent with this hypothesis, M. persicae populations induced ABA production in wild‐type plants. Furthermore, aphid populations were smaller on Arabidopsis aba1‐1 mutants, which cannot synthesize ABA, and showed a significant preference for wild‐type plants compared with the mutant. Total free amino acids, which play an important role in aphid nutrition, were not altered in the aba1‐1 mutant line, but the levels of isoleucine (Ile) and tryptophan (Trp) were differentially affected by aphids in wild‐type and mutant plants. Recently, indole glucosinolates have been shown to promote aphid resistance in Arabidopsis. In this study, 4‐methoxyindol‐3‐ylmethylglucosinolate was more abundant in the aba1‐1 mutant than in wild‐type Arabidopsis, suggesting that the induction of ABA signals that decrease the accumulation of defence compounds may be beneficial for aphids.     

Seasonal changes in the distribution of green spruce aphid Elatobium abietinum (Walker) (Homoptera: Aphididae) in the canopy of Sitka spruce

1 Seasonal changes in the distribution of green spruce aphid Elatobium abietinum (Walker) within the canopy of 20–25‐year‐old Sitka spruce are described based on data from two low‐altitude sites (310–420 m above sea‐level), two mid‐altitude sites (500–550 m a.s.l) and one high‐altitude site (610 m a.s.l). 2 Aphids were counted throughout the canopy on shoots representative of all needle age‐classes present at each whorl of branches. Counts were made during the middle week of each month from September to July for 4 years (1999–2003), and mean E. abietinum densities at each canopy position were calculated separately for each month and for the low‐, mid‐ and high‐altitude sites. 3 During September to November, the highest densities of E. abietinum occurred on 3–4‐year‐old needles on branches low in the canopy. Over the winter and spring, the centre of the aphid’s distribution shifted outward and upward, so that by June of the next year the highest aphid densities occurred on current and 1‐year‐old needles on branches near the top of the tree. 4 The aphid distribution was re‐set each year during July, at the time when the nutrient quality of the host was in decline and E. abietinum populations were decreasing. Aphid densities decreased less on 3–4‐year‐old needles than on current and 1‐year‐old needles, suggesting that older needles were a superior food resource at this time of year and in the autumn. However, other factors, such as higher temperatures in the upper canopy during the summer or differential mortality caused by natural enemies, could also have contributed to the change in distribution. 5 The outward and upward shift in the aphid distribution over the winter period provided no evidence that aphids at positions lower and deeper in the canopy were better insulated from freezing temperatures and had higher over‐winter survival rates. Mean air temperatures at the top and bottom of the canopy during the winter were also found to differ by only 0.1–0.2 °C. 6 The percentage of the total aphids per tree that occurred on current or 1‐year‐old needles varied widely between seasons and between sites. Consequently, sampling programmes designed to estimate total population numbers of E. abietinum have little option but to sample needles throughout the canopy, and at regular intervals during the period when the aphid is abundant.     

The effect of ant attendance on the success of rosy apple aphid populations, natural enemy abundance and apple damage in orchards

1 The rosy apple aphid, Dysaphis plantaginea, is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention. 2 An ant exclusion study was conducted in two distant orchards within the U.K. At both sites, ants were excluded from a subset of D. plantaginea infested trees at the beginning of the season and populations were monitored. The number of natural enemies observed on trees was also recorded and, before harvest, the percentage of apples damaged by D. plantaginea calculated. 3 Overall, the exclusion of ants reduced the growth and eventual size of D. plantaginea populations. On trees accessed by ants, greater numbers of natural enemies were recorded, presumably because aphid populations were often greater on such trees. However, this increased natural enemy presence was diluted by the larger aphid populations such that individual aphids on ant‐attended trees were subjected to a lower natural enemy pressure compared with those on ant‐excluded trees. 4 At harvest, apple trees that had been accessed by ants bore a greater proportion of apples damaged by D. plantaginea. There were also differences in cultivar susceptibility to D. plantaginea damage. 5 The present study highlights the importance of the ant–D. plantaginea relationship and it ia suggested that ant manipulation, whether physically or by semiochemicals that disrupt the relationship, should be considered as a more prominent component in the development of future integrated pest management strategies.     

Aphid suppression by natural enemies in mulched cereals

Large populations of natural enemies are the basis for natural pest control. Effects of mulch on predator–prey interactions in arable fields are poorly known, despite its potential to enhance ground‐dwelling predators and thereby reduce pest infestations. We studied the densities of predators and parasitoids, and their impact on cereal aphids in the presence and absence of mulch. Released populations of the bird cherry aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), and two naturally occurring aphid species, were monitored under experimentally reduced densities of: (i) ground‐dwelling predators, (ii) flying predators and parasitoids, and (iii) with straw mulch. The three treatments were applied in a 2 × 2 × 2 factorial design in a field of spring wheat (Triticum aestivum L.). The exclusion of ground‐dwelling predators increased aphid populations by 55% in June and 40% in July, respectively. Mulched plots had 25% lower aphid densities in June. This was presumably due to enhanced densities of spiders (Araneida) in mulched plots. The exclusion of flying predators and parasitoids led to 94% higher aphid populations in late July (109 vs. 56 individuals per 100 shoots), irrespective of mulch or ground predator manipulation. This was attributed to the larvae of gall midges Aphidoletes cf. aphidimyza (Rondani) (Diptera: Cecidomyiidae) and hoverflies (Diptera: Syrphidae). The results indicate that a scarcity of predators and a bare soil surface renders crops more susceptible to arthropod pests. Farming schemes should aim at enhancing both ground‐dwelling and flying predators for elevated levels of natural pest control.     

Models for spring migration of two aphid species Sitobion avenae (F.) and Rhopalosiphum padi (L.) infesting cereals in areas where they are entirely holocyclic

1 Cereals can be attacked severely by the grain aphid, Sitobion avenae (F.), and the bird cherry‐oat aphid, Rhopalosiphum padi (L.). The time of migration from winter hosts in spring is important regarding input to decision support systems concerning insecticide treatment of aphids. 2 The present study aimed to construct two separate migration models, which could be used immediately for advisors and farmers but also be part of a decision support system for the chemical control of aphids in winter wheat and spring barley. 3 Winter wheat (Triticum sativum Lam.) and spring barley (Hordeum vulgare L.) fields were monitored from 1991–2005 for the occurrence of grain aphids and bird cherry‐oat aphids, and the data were used to construct migration models. 4 The models were constructed based on all 9 years data and subsequently validated by using all 9 years data, excluding 1 year at a time. 5 The migration model for the grain aphid producing the best forecast was obtained with migration date M (number of days from 1 June), degree‐days (DD) of April (T_a) and DD of May (T_m), with the model being M= 265.0 ? 10.2 log_e(T_a) ? 35.1 log_e(T_m). 6 The migration model for the bird cherry‐oat aphid producing the best forecast was obtained with migration date M (number of days from 15 May), DD of April (T_a) and DD from 1–15 May (T_m1), with the model being M= 294.4 ? 34.7 log_e(T_a) ? 22.5 log_e(T_m1). 7 The models only worked well in areas where the grain aphid and the bird cherry‐oat aphid are entirely holocyclic.     

Efficacy of Three Strategies Based on Insecticide,Oil and Elicitor Treatments in Controlling Aphid Populations and Potato virus Y Epidemics in Potato Fields

Potato virus Y (PVY), the potato virus with the highest economic impact in Europe, is transmitted by aphids in a non‐persistent manner. A two‐year field experiment was conducted in Switzerland to evaluate the efficacy of three strategies for controlling aphid populations and the spread of PVY, consisting of treatment with one insecticide (Karate Zeon^®), one elicitor (Bion^®) and one oil (Telmion^®), respectively. The elicitor strategy proved to be ineffective for controlling aphid populations and inadequate for controlling PVY spread. The insecticide strategy gave incomplete protection from aphid infestations, owing to the selection of aphid‐resistant clones. The insecticide gave too little protection against PVY spread for it to be considered a suitable candidate for the purpose. The oil strategy had no effect on aphid populations, but was the best option to reduce PVY spread.     

First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose–mortality regressions, 50% lethal concentrations (LC₅₀), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter‐population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀: 1.0–13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter‐population variation in the phenotypic level of resistance was evident (RRs at LC₅₀: 1.0–104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.     

Comparative population structure of Chinese sumac aphid <Emphasis Type="Italic">Schlechtendalia chinensis</Emphasis> and its primary host-plant <Emphasis Type="Italic">Rhus chinensis</Emphasis>

Most of our current understanding of comparative population structure has been come from studies of parasite–host systems, whereas the genetic comparison of gallnut-aphids and their host-plants remain poorly documented. Here, we examined the population genetic structure of the Chinese sumac aphid Schlechtendalia chinensis and its unique primary host-plant Rhus chinensis in a mountainous province in western China using inter-simple sequence repeat (ISSR) markers. Despite being sampled from a mountainous geographic range, analysis of molecular variance (AMOVA) showed that the majority of genetic variation occurred among individuals within populations of both the aphid and its host. The aphid populations were found to be structured similarly to their primary host populations (F _ST values were 0.239 for the aphid and 0.209 for its host), suggesting that there are similar patterns of gene flow between the populations of the aphid and between populations of its host-plant. The genetic distances (F _ST/1 − F _ST) between the aphid populations and between its host-plant populations were uncorrelated, indicating that sites with genetically similar host-plant populations may not always have genetically similar aphid populations. The lack of relationships between genetic and geographical distance matrices suggested that isolation by distance (IBD) played a negligible role at this level. This may be mainly attributed to the founder effect, genetic drift and the relative small spatial scale between populations. Zhumei Ren and Bin Zhu contributed equally to this work.     

Suction‐trap catches partially predict infestations of the grain aphid Sitobion avenae in winter wheat fields

Effective pest monitoring programmes are needed for providing reliable advice on when pest populations require active management. We studied whether suction‐trap catches of the grain aphid Sitobion avenae during the period 1989–2009 can be used to predict field infestations of this aphid in Swedish winter wheat fields. We found that suction‐trap catches of S. avenae until the time of crop heading (GS51) were significantly related to both number of aphids per tiller (R² = 0.69 at GS 59 and R² = 0.27 at GS 69) and proportion of fields with infestations above economic threshold (R² = 0.49 at GS 59 and R² = 0.40 at GS 69). This effect was consistent across Swedish regions and years. This information could be used by advisory services and farmers to decide whether field inspection to estimate the profitability of insecticide treatment at heading is needed. To improve the predictive ability further, suction‐trap catches could be combined with weather data and information about biological control potential in different landscapes.