Spatial and temporal patterns of onion maggot adult activity and oviposition within onion fields that vary in bordering habitat

In New York, onion [ Allium cepa L. (Alliaceae)] fields often border woods or other vegetable fields. Because onion maggot adults, Delia antiqua (Meigen) (Diptera: Anthomyiidae), spend a significant portion of their time outside of onion fields, surrounding habitat may affect patterns of fly activity and oviposition within onion fields. To better understand these patterns throughout the onion-growing season, first-, second-, and third-flights maggot adult (male and female) activity was monitored using yellow sticky cards. Half of the monitored fields bordered woods, whereas the other half bordered other onion or vegetable fields. Within all fields, yellow sticky cards were placed at five distances along a transect beginning at the onion field edge extending into the field center. First-flight male and female adult activity was greatest along onion field edges and was especially high along edges bordering woods. This pattern diminished during the second flight and was absent during the third. To determine if spatial patterns of onion maggot oviposition by first-flight onion maggots were similar to first-flight adult activity patterns, potted onion plants were placed in onion fields that bordered or did not border woods in late May and early June 2003. The number of eggs laid in the soil at the base of each plant was recorded. Unlike spatial patterns of first-flight adult activity, oviposition patterns were not affected by bordering habitat or distance from the field edge. Based on the activity of onion maggot adults in onion fields, future and existing control strategies should consider targeting first-flight adults along field edges rather than across entire fields, especially in fields that border woods. In contrast, based on spatial patterns of oviposition within onion fields, controls targeting onion maggot larvae should be applied on a fieldwide basis.     

Impacts of elevated CO2 on Bemisia tabaci infesting Bt cotton and its parasitoid Encarsia formosa

Atmospheric carbon dioxide concentration is expected to rise in the coming decades. Rising atmospheric CO₂ levels may alter plant‐insect‐parasitoid associations due to the indirect effects of CO₂ enrichment on phytochemicals important for herbivore and parasitoid nutrition. Tritrophic effects of elevated CO₂ on Bt cotton (GK‐12) and non‐transgenic (Simian‐3, or S3) cotton [Gossypium hirsutum L. (Malvaceae)], Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae), and its parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae), were examined in open‐top chambers. Significantly, longer egg‐adult developmental duration and higher mortality of nymphs were observed under elevated CO₂ concentrations on both cotton cultivars during three successive generations. However, no significant differences were found in adult longevity, offspring sex ratio, and the number of eggs laid per female adult of B. tabaci fed on transgenic (GK‐12) or non‐transgenic cotton (S3) grown under elevated CO₂. Abundance of B. tabaci adults increased from 10 to 120 per plant and then decreased to 40 per plant through the growing season, but no significant differences in density occurred between CO₂ treatments and between cultivar treatments. Similarly, no significant differences were found in the developmental duration, parasitization rate, and adult emergence rate of E. formosa after parasitizing B. tabaci for three successive generations. Our results showed that the effects of transgenic Bt cotton did not significantly affect the development, survivorship, life span, or fecundity of B. tabaci and its parasitoids. Moreover, interactions between B. tabaci and E. formosa were not significantly affected by elevated CO₂. These results suggest that the biological control of B. tabaci by E. formosa would not be influenced by transgenic Bt cotton and/or elevated CO₂, indicating that the current risk management strategy regarding B. tabaci outbreaks and biocontrol by E. formosa will remain effective if the atmospheric CO₂ level continues to rise.     

Contrasting Demographic Structure of Short‐ and Long‐lived Pioneer Tree Species on Amazonian Forest Edges

Although tropical forests have been rapidly converted into human‐modified landscapes, tree species response to forest edges remains poorly examined. In this study, we addressed four pioneer tree species to document demographic shifts experienced by this key ecological group and make inferences about pioneer response to forest edges. All individuals with dbh ≥ 1 cm of two short‐lived (Bellucia grossularioides and Cecropia sciadophylla) and two long‐lived species (Goupia glabra and Laetia procera) were sampled in 20 1‐ha forest edge plots and 20 1‐ha forest interior plots in Oiapoque and Manaus, Northeast and Central Amazon, respectively. As expected, pioneer stem density with dbh ≥ 1 cm increased by around 10–17‐fold along forest edges regardless of species, lifespan, and study site. Edge populations of long‐lived pioneers presented 84–94 percent of their individuals in sapling/subadult size classes, whereas edge populations of short‐lived pioneers showed 56–97 percent of their individuals in adult size classes. These demographic biases were associated with negative and positive net adult recruitment of long‐ and short‐lived pioneers, respectively. Our population‐level analyses support three general statements: (1) native pioneer tree species proliferate along forest edges (i.e., increased density), at least in terms of non‐reproductive individuals; (2) pioneer response to edge establishment is not homogeneous as species differ in terms of demographic structure and net adult recruitment; and (3) some pioneer species, particularly long‐lived ones, may experience population decline due to adult sensitivity to edge‐affected habitats.     

Effects of Tomato chlorosis virus on the performance of its key vector,Bemisia tabaci,in China

Tomato chlorosis virus (ToCV), which is a newly emerged and rapidly spreading plant virus in China, has seriously reduced tomato production and quality over the past several years. In this study, the effect of ToCV on the demography of the whitefly, Bemisia tabaci biotype Q (Hemiptera: Aleyrodidae), fed on infected and healthy tomato plants was evaluated using the age‐stage, two‐sex life table. When reared on ToCV‐infected tomato plants, the fecundity, length of oviposition period and female adult longevity of B. tabaci biotype Q decreased significantly, while the pre‐adult duration significantly increased compared to controls reared on healthy tomatoes. Consequently, the intrinsic rate of increase (r) and finite of increase (λ) of B. tabaci biotype Q on ToCV‐infected tomato plants significantly decreased compared to those on healthy tomatoes. Population projection predicted that a population of B. tabaci biotype Q fed on ToCV‐infected tomatoes increases slower than on healthy plants. These findings demonstrated that ToCV infection decreased the performance of B. tabaci biotype Q on tomato plants.     

Colonization of potato fields in eastern North Carolina by Colorado potato beetle

Rotated and non-rotated commercial potato fields were sampled intensively to follow Colorado potato beetle,Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), colonization and subsequent oviposition patterns in the spring of 1990 and 1991. Maximum densities of colonizing adults ranged from 0 to 14,891/ha and maximum egg mass densities ranged from 0 to 48,451/ha. Crop rotation generally resulted in lower potato beetle populations. Regardless of crop rotation management practices, colonization of fields planted in potatoes began at field edges and progressed inward in all fields for both years. Management of potato beetles is discussed in light of these findings.     

Distribution and activity of Drosophila suzukii in cultivated raspberry and surrounding vegetation

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), may utilize wild ‘Himalaya’ blackberry (HB) Rubus armeniacus Focke or other non‐crop plants as refugia and possibly exploit adjacent field margins before colonizing cultivated fruiting crops. Studies were conducted to determine the role of field margins containing HB and their effect on D. suzukii activity, density and distribution in an adjacent commercial red raspberry crop. One‐ha plots adjacent to field margins containing HB or known non‐host (NH) grass crops were established in 2011 and 2012 and replicated three times. Each plot contained two transects with monitoring traps for D. suzukii in the field margin (0 m) and spaced approximately 10 (crop boundary), 40, 70 and 100 m into the adjacent crop (n = 10 traps/plot). Field margin vegetation was treated with a 10% chicken egg white mark solution weekly from pre‐harvest until the end of harvest using a cannon sprayer. Adult D. suzukii were collected from traps weekly and analysed for the presence of the egg white mark using an egg white‐specific enzyme‐linked immunosorbent assay (ELISA). During both years, marked flies and total flies were captured in higher numbers in HB field margins, whereas virtually no flies were captured in field margins containing no known alternative host. Similarly, more flies were captured in the crop near HB than near NH. Spatial Analysis by Distance IndicEs (SADIE) and mean D. suzukii trap captures additionally displayed significantly higher fly densities in the raspberry field near HB than near NH. These results suggest that HB may contribute to elevated D. suzukii populations and pest pressure in comparison with field margins containing no known alternate host vegetation for D. suzukii. Having closely adjacent non‐crop alternate host landscapes may result in increased D. suzukii pest pressure.     

Influence of the surrounding landscape on crop colonization by a polyphagous insect pest

Landscape composition plays an important, but poorly understood, role in the population dynamics of agricultural pest species with broad host ranges including both crops and weeds. One such pest, the generalist plant bug Lygus hesperus Knight (Hemiptera: Miridae), is a key cotton pest that feeds on various hosts differing in quality in California's San Joaquin Valley (USA). We investigated the effects of 15 common crops and uncultivated agricultural land on L. hesperus populations, by correlating the densities of L. hesperus in focal cotton fields with the areas of the 16 crops in surrounding rings. Insect counts were provided by private pest‐control advisors, and spatial data were obtained from Kern County records. We first calculated Spearman's partial correlation coefficients on an annual basis for each crop separately, and then performed a meta‐analysis of these correlations across years to describe the overall effect of a particular crop on L. hesperus after the effects of the 15 other crops are removed. Consistent with studies conducted in other areas, L. hesperus density was positively correlated with safflower, and negatively with cotton. Lygus hesperus density was also correlated with several other crops that are often not considered in pest management, including grape, oat, and onion (positive correlations), and almond, pistachio, and potato (negative correlations). Lygus hesperus density was also found to be negatively correlated with alfalfa and positively correlated with uncultivated habitats, a relationship that receives mixed support in the literature. Several other crops tested were not significantly correlated with L. hesperus densities in focal cotton fields, suggesting a neutral role for them in L. hesperus dynamics. The improved understanding of the effects of a greater variety of crops on L. hesperus population dynamics will be useful in the design of agricultural landscapes for enhanced management of this important polyphagous pest.     

Annual flower strips support pollinators and potentially enhance red clover seed yield

Ecological intensification provides opportunity to increase agricultural productivity while minimizing negative environmental impacts, by supporting ecosystem services such as crop pollination and biological pest control. For this we need to develop targeted management solutions that provide critical resources to service‐providing organisms at the right time and place. We tested whether annual strips of early flowering phacelia Phacelia tanacetifolia support pollinators and natural enemies of seed weevils Protapion spp., by attracting and offering nectar and pollen before the crop flowers. This was expected to increase yield of red clover Trifolium pratense seed. We monitored insect pollinators, pests, natural enemies and seed yields in a total of 50 clover fields along a landscape heterogeneity gradient, over 2 years and across two regions in southern Sweden. About half of the fields were sown with flower strips of 125–2,000 m². The clover fields were pollinated by 60% bumble bees Bombus spp. and 40% honey bees Apis mellifera. The clover seed yield was negatively associated with weevil density, but was unrelated to bee species richness and density. Flower strips enhanced bumble bees species richness in the clover fields, with the strongest influence in heterogeneous landscapes. There were few detectable differences between crop fields with and without flower strips. However, long‐tongued bumble bees were redistributed toward field interiors and during phacelia bloom honey bees toward field edges. Clover seed yield also increased with increasing size of the flower strip. We conclude that annual flower strips of early flower resources can support bumble bee species richness and, if sufficiently large, possibly also increase crop yields. However, clover seed yield was mainly limited by weevil infestation, which was not influenced by the annual flower strips. A future goal should be to design targeted measures for pest control.     

Responses of Thrips tabaci to odours of herbivore‐induced cotton seedlings

Herbivore‐induced changes in plants have been widely viewed as defensive responses against further insect attack. However, changes in plants as a consequence of herbivore feeding can elicit various responses in herbivores; these are variable, context dependent, and often unpredictable. In this laboratory study, the responses of Thrips tabaci Lindeman (Thysanoptera: Thripidae) to volatiles emitted by intact and herbivore‐damaged or mechanically damaged cotton seedlings [Gossypium hirsutum L. (Malvaceae)] were investigated in dual‐choice olfactometer assays. Thrips tabaci showed increased attraction to seedlings subject to foliar mechanical damage and those with foliar damage inflicted by conspecifics or Tetranychus urticae Koch (Acari: Tetranychidae), upon which it preys. However, T. tabaci did not discriminate between intact seedlings and those with foliar damage inflicted by Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), two other species of thrips, Frankliniella schultzei Trybom and Frankliniella occidentalis Pergrande (Thysanoptera: Thripidae), or those with root damage inflicted by Tenebrio molitor L. (Coleoptera: Tenebrionidae). Attraction of T. tabaci was also affected by herbivore density on damaged plants. That is, seedlings damaged by higher densities of T. urticae or T. tabaci were more attractive than seedlings damaged by lower densities of the corresponding arthropod. Although attracted to plants damaged by conspecifics or T. urticae, T. tabaci showed greater attraction to seedlings damaged by T. urticae than to seedlings damaged by conspecifics. Results are discussed in the context of the responses of F. schultzei and F. occidentalis to herbivore‐induced cotton seedlings, highlighting the complexity, variability, and unpredictability of the responses of even closely related species of insects to plants under herbivore attack.     

Within‐field spatial distribution patterns of corn planthopper,Peregrinus maidis,and severity of hopperburn and Maize mosaic virus symptoms as influenced by sunn hemp intercropping

Habitat management (e.g., intercropping) may alter within‐field spatial distribution patterns of herbivores, from a typical pattern as observed in a monoculture, and may influence patterns of crop injury. Field trials were conducted to study the effect of intercropping maize, Zea mays L. (Poaceae), with sunn hemp, Crotalaria juncea L. (Fabaceae) strips on within‐field spatial distribution patterns of corn planthopper, Peregrinus maidis (Ashmead) (Hemiptera: Delphacidae), and combined severity of hopperburn and Maize mosaic virus (MMV) (Rhabdoviridae: Nucleorhabdovirus) symptoms. In each field trial, spatially explicit data on P. maidis counts and ratings of severity of symptoms were obtained by sampling maize plants at weekly intervals. These data were used to examine the spatial patterns of P. maidis and severity of symptoms in maize‐intercropped and monoculture plots with Spatial Analysis for Distance IndicEs (SADIE) methodology. Spatial aggregation patterns of P. maidis in each treatment plot were not consistent among the field trials and tended to be mediated by their population densities. Interpolation of local cluster indices showed that P. maidis were more often aggregated at the field edges, irrespective of treatment. At times of MMV incidence in field trials (fall 2010 and spring 2011), the patch clusters of P. maidis and symptomatic plants were located at the field edges, but were spatially unassociated in both treatment plots. The results provided an approximation of the unpredictability of P. maidis spatial patterns at different population densities and their association with severity of symptoms in two maize‐cropping systems. However, the gap clusters of symptomatic plants were primarily located at the field interiors and were larger in intercropped than in monoculture plots. Such spatial pattern of symptomatic plants resulted in the reduced incidence of MMV in the intercropped plot compared with the monoculture plot, suggesting intercropping sunn hemp can be a useful tool in the management of MMV in maize fields.     

Effect of a novel repellent,acetylated glyceride,on courtship behaviours and acoustic signals of Bemisia tabaci

The sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), attacks a wide range of vegetables and ornamental plants in the tropics and subtropics. This study involved observations of adult whitefly courtship behaviours to determine the impact of acetylated glyceride treatment, which is currently being developed as a repellent for adults, on their progeny. In addition, the effect of acetylated glyceride treatment on acoustic‐based communication was evaluated, as this type of communication is known to play a pivotal role in the search for mating partners on host‐plant leaves in adult whiteflies. Adults were able to land on grape tomato leaves a few days after treatment, when the residual repellency had dissipated. Almost no male courtship behaviour in terms of searching for sexually mature females was observed throughout the observation period (60 min) under conditions in which adults of both sexes remained on a treated leaf or those in which an adult of either sex remained on a non‐treated leaf. By contrast, these behaviours accounted for 26.5% of the observation time under conditions in which both sexes remained on a non‐treated leaf. In cross‐tests performed for 4 days using one non‐mated female and two non‐mated males, the sex ratio (male/female) of the newly emerged adults on treated leaves (2.4) was 63.6% lower than that of the non‐treated controls (0.9). During courtship, acoustic signals produced by both sexes were exchanged rhythmically on non‐treated leaves, whereas the signals on treated leaves were irregular. The frequency of the vibratory sound produced by males was 66–81% lower on the treated leaves than on the non‐treated leaves. A large reduction in the acoustic signals produced by males on treated leaves caused a decrease in courting pair formation, leading to a significant reduction in the number of female progeny due to arrhenotokous parthenogenesis in virgin B. tabaci females.     

A multiple PCR‐LDR assay for identification of two invasive cryptic species of whiteflies Bemisia tabaci

The MEAM1 and MED species of the cryptic species complex Bemisia tabaci are important invasive pests that cause tremendous crop losses worldwide. A rapid and highly reliable molecular technique is necessary to identify these species because they are morphologically indistinguishable. Therefore, a multiple polymerase chain reaction coupled with a ligase detection reaction (PCR‐LDR) that was based on polymorphisms in the mitochondrial cytochrome oxidase I (mtCOI) gene of B. tabaci was developed to distinguish the two cryptic species. An assessment of the method indicated that PCR‐LDR provided high specificity and sensitivity in discriminating MEAM1 (SHB) and MED (SHQ) whiteflies. In field tests, PCR‐LDR genotyping was performed in one 96‐well plate to identify 93 individuals collected from 8 districts in the suburbs of Shanghai. Complete concordance was observed between PCR‐LDR and sequencing methods. The method was used to confirm that MEAM1 and MED were found in two districts, but only the MED was found in the other six districts. PCR‐LDR, which is a transplantable platform, provides an alternative method for species identification of B. tabaci at low cost.     

Genetic diversity and geographic distribution of Bemisia tabaci and Trialeurodes vaporariorum in Costa Rica

The tobacco whitefly Bemisia tabaci (Gennadius) cryptic species complex and of the greenhouse whitefly Trialeurodes vaporariorum (Westwood) are extensively reported as destructive pests in vegetable crops worldwide. A survey was conducted in 2011 and 2012 to determine the occurrence and genetic diversity present in the populations of these whiteflies in the major vegetable production areas of Costa Rica. Insect samples were collected from sweet pepper (Capsicum annuum L.), tomato (Solanum lycopersicum L.), common bean (Phaseolus vulgaris L.) and weeds present in commercial crops either in open field or greenhouse conditions. PCR‐RFLP analysis of mitochondrial cytochrome c oxidase subunit 1 gene (mtCOI) sequences of 621 whitefly individuals confirmed the presence of the Mediterranean (MED) type of the B. tabaci and of T. vaporariorum in most sampled regions. Also, individuals of the Middle East‐Asia Minor 1 (MEAM1) type of the B. tabaci were observed in low numbers. Contingency analyses based on type of crop, geographical region, whitefly species, year of collection and production system confirmed that T. vaporariorum was the most frequent species in vegetable production areas in Costa Rica, both in greenhouses and in open fields. B. tabaci MED is likely spreading to new areas of the country, whereas B. tabaci MEAM1 was mostly absent or rarely found. Comparisons of mtCOI sequences from B. tabaci individuals revealed the presence of four B. tabaci sequence haplotypes (named MED‐i, MED‐ii, MEAM1‐i, MEAM1‐xviii) in Costa Rica, three of them identical to B. tabaci haplotypes previously reported in the Western Hemisphere and other parts of the world. Analysis of sequences of T. vaporariorum individuals revealed a more complex population with the presence of 11 haplotypes, two of which were identical to T. vaporariorum sequences reported from other countries.     

Intercropping oilseed rape as a potential relay crop for enhancing the biological control of green peach aphids and aphid‐transmitted virus diseases

Tobacco viruses transmitted by green peach aphids, Myzus persicae (Sulzer) (Hemiptera: Aphididae), cause severe disease in flue‐cured tobacco, Nicotiana tabacum L. (Solanaceae), in China and throughout the world. Field experiments were conducted in 2016 and 2017 in Longyan City, Fujian Province, China, to determine whether M. persicae and aphid‐transmitted virus diseases are affected by intercropping of oilseed rape, Brassica napus L. (Brassicaceae), in tobacco fields. The results showed that, compared with those in monocultured fields, the densities of M. persicae and winged aphids in intercropped fields significantly decreased in both 2016 and 2017. In particular, the appearance of winged aphids was delayed by ca. 7 days. Moreover, the densities of Aphidius gifuensis Ashmead (Hymenoptera: Aphidiidae), a parasitoid of the aphid, significantly increased in 2016 and 2017. Accordingly, the incidence rates of aphid‐transmitted virus diseases (those caused by the cucumber mosaic virus, potato virus Y, and tobacco etch virus) significantly decreased in the intercropped fields in 2016 and 2017. Tobacco yields and monetary value significantly increased in 2016 (by 10–25 and 14–29%, respectively) and 2017 (by 17–22 and 22–34%, respectively). Consequently, our results suggest that intercropping oilseed rape in tobacco fields is a good approach to regulating and controlling aphids and tobacco mosaic viruses, for example potyvirus, and this intercropping can help control aphid‐transmitted virus diseases in tobacco.     

Regional assessment of Helicoverpa zea populations on cotton and non-cotton crop hosts

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.     

Mix‐planting pubescent and glabrous cassava affects abundance of Typhlodromalus aripo and its prey mite Mononychellus tanajoa

There is an increasing awareness that vegetation diversity can affect herbivore and natural enemy abundance and that plants can play a major role in directly manipulating natural enemy abundance for protection against herbivore attacks. Using data from cassava fields, we aimed at (i) testing the capacity of the predatory mite Typhlodromalus aripo to control the herbivorous mite Mononychellus tanajoa in a chemical exclusion trial; and (ii) testing, based on the differential preference by T. aripo for cassava cultivars, how combinations of two morphologically different cassava cultivars with differential suitability to the predator can improve its population densities on the non‐favourable cultivar, thereby reducing M. tanajoa densities with subsequent increases in cassava yield. The study was conducted in a cassava field in Benin, West Africa. The experiments confirmed that T. aripo effectively suppresses M. tanajoa populations on both cultivars and showed, in the no‐predator‐exclusion experiments, that cultivar combinations have significant effects on M. tanajoa and T. aripo densities. Indeed, T. aripo load on the non‐preferred cultivar was lowest in subplots where the proportion of T. aripo‐preferred cultivar was also low, while, and as expected, M. tanajoa load on the non‐preferred cultivar showed decreasing trends with increasing T. aripo densities. The possible mechanisms by which cultivar mixing could increase predator load on the non‐favourable cultivar were discussed. Our data showed that appropriate cultivar combinations effectively compensate for morphologically related differences in natural enemy abundance on a normally predator‐deficient cultivar, resulting in lower pest densities on the non‐favourable cultivar. In practical terms, this strategy could, in part, enhance adoption of cultivars that do not support sufficient levels of natural enemies for pest control.     

The influence of crop rotation on the onset of early blight (Alternaria solani)

Field experiments were carried out in 2016 and 2017 to determine the effect of crop rotation on the onset of early blight in three potato varieties in Denmark. Six and seven fields with different histories with potato (rotation‐fields) were used for the experiments in 2016 and 2017, respectively. The results showed that variety and the interaction between variety and rotation‐field had no significant effect on the onset of early blight. Rotation‐field, on the other hand, had a significant effect on the onset of early blight in both years of the study. Early blight occurred earlier in fields with <2 years between subsequent potato crops than in fields where potatoes have not been grown for at least 2 years. The onset of early blight was not different between the fields where there had not been potatoes for at least 2 years. For fields that were preceded by potatoes, early blight occurred earlier in fields in which the severity of early blight in the previous years was higher than that in the fields in which the severity of early blight in the previous years was low or moderate. In conclusion, the results of this study suggest that at least a 2‐year interval between subsequent potatoes in a rotation cycle is necessary to delay the onset of early blight. Moreover, the severity of early blight in the previous years can affect the onset of early blight.     

Bacillus thuringiensis plants expressing Cry1Ac,Cry2Ab and Cry1F are not toxic to the assassin bug,Zelus renardii

Cotton‐ and maize‐producing insecticidal crystal (Cry) proteins from the bacterium, Bacillus thuringiensis (Bt), have been commercialized since 1996. Bt plants are subjected to environmental risk assessments for non‐target organisms, including natural enemies that suppress pest populations. Here, we used Cry1F‐resistant Spodoptera frugiperda (J.E. Smith) and Cry1Ac and Cry2Ab‐resistant Trichoplusia ni (Hübner) as prey for the assassin bug, Zelus renardii (Kolenati), a common predator in maize and cotton fields. In tritrophic studies, we assessed several fitness parameters of Z. renardii when it fed on resistant S. frugiperda that had fed on Bt maize expressing Cry1F or on resistant T. ni that had fed on Bt cotton expressing Cry1Ac and Cry2Ab. Survival, nymphal duration, adult weight, adult longevity and female fecundity of Z. renardii were not different when they were fed resistant‐prey larvae (S. frugiperda or T. ni) reared on either a Bt crop or respective non‐Bt crops. ELISA tests demonstrated that the Cry proteins were present in the plant at the highest levels, at lower levels in the prey and at the lowest levels in the predator. While Z. renardii was exposed to Cry1F and Cry1Ac and Cry2Ab when it fed on hosts that consumed Bt‐transgenic plants, the proteins did not affect important fitness parameters in this common and important predator.     

Differences in host selection and performance between B and Q putative species of Bemisia tabaci on three host plants

B and Q are two putative species of the Bemisia tabaci complex (Hemiptera: Aleyrodidae), and are among the most invasive and destructive pests of crops and horticultural plants worldwide. In China, Q predominates and is displacing B. Although researchers have proposed that the higher capacity of Q to utilize host plants plays an important role in its replacement of B, there are few relevant field surveys and experimental studies. The difference in host assessment between B and Q in multiple‐choice rather than in no‐choice situations may be essential to understanding the displacement. Here, we compared settling and oviposition preferences, and adult and nymph performance, for the putative species B and Q of the B. tabaci complex on three common host species: poinsettia [Euphorbia pulcherrima Wild. ex Klotsch (Euphorbiaceae)], cotton [Gossypium hirsutum L. (Malvaceae)], and cabbage [Brassica oleracea L. (Brassicaceae)]. Although the preferred hosts for settling and oviposition were the same as those that supported maximum fitness (adult longevity, fecundity, and nymph survivorship), these hosts differed between B and Q. When given a choice, B preferred to settle and oviposit on cabbage over poinsettia and cotton, whereas Q preferred to settle and oviposit on poinsettia and cotton over cabbage. In a no‐choice experiment, adult longevity, fecundity, and nymphal survival for B were greater on cabbage than on poinsettia and cotton, but the opposite was true for Q.