Pristionchus uniformis,should I stay or should I go? Recent host range expansion in a European nematode

Pristionchus pacificus has been developed as a model system in evolutionary developmental biology, evolutionary ecology, and population genetics. This species has a well-known ecological association with scarab beetles. Generally, Pristionchus nematodes have a necromenic association with their beetle hosts. Arrested dauer larvae invade the insect and wait for the host's death to resume development. Only one Pristionchus species is known to frequently associate with a non-scarab beetle. Pristionchus uniformis has been isolated from the chrysomelid Leptinotarsa decemlineata, also known as the Colorado potato beetle, in Europe and North America, but is also found on scarab beetles. This unusual pattern of association with two unrelated groups of beetles on two continents requires the involvement of geographical and host range expansion events. Here, we characterized a collection of 81 P. uniformis isolates from North America and Europe and from both scarab beetles and L. decemlineata. We used population genetic and phylogenetic analyses of the mitochondrial gene nd2 to reconstruct the genetic history of P. uniformis and its beetle association. Olfactory tests on beetles chemical extracts showed that P. uniformis has a unique chemoattractive profile toward its beetle hosts. Our results provide evidence for host range expansion through host-switching events in Europe where P. uniformis was originally associated with scarab beetles and the nematode's subsequent invasion of North America.     

Resistance potential of colorado potato beetle (Coleoptera: Chrysomelidae) to novaluron

Novaluron (Rimon 10 EC), a novel insect growth regulator, could play an important role in future management programs for Colorado potato beetle, Leptinotarsa decemlineata (Say). Studies were conducted to determine the potential of Colorado potato beetle to develop resistance to novaluron before its widespread use in Colorado potato beetle management. Second instars of an imidacloprid-resistant Colorado potato beetle strain exhibited reduced susceptibility (2.5-fold) to novaluron. The toxicity of novaluron to this strain was synergized by S,S,S-tributyl phosphorotrithioate (DEF) but not by piperonyl butoxide (PBO), suggesting that esterase-based detoxification mechanisms were responsible for novaluron resistance. Bioassays with treated potato foliage found that a single low- or medium-rate novaluron application was highly persistent under field conditions, resulting in up to 85% mortality of second instars 5 wk after treatment. Thus, intense selection pressure for novaluron-resistant Colorado potato beetle may continue long after population densities have been reduced below an economic threshold level. In a national survey, the susceptibility of second instars to a novaluron diagnostic dose was determined for 27 different field populations collected from six Canadian provinces in summer 2003. Despite no previous exposure to novaluron, mortalities at the diagnostic dose ranged from 55 to 100%. Although novaluron has several characteristics that should delay resistance development in insect pests, these results highlight the need for judicious use of the compound in management of Colorado potato beetle.     

Insecticidal activity of avidin combined with genetically engineered and traditional host plant resistance against Colorado potato beetle (Coleoptera: Chrysomelidae) larvae

Colorado potato beetle, Leptinotarsa decemlineata (Say), is a destructive pest of potato, Solanum tuberosum (L.), in North America. It is renowned for adapting to insecticides. With the arsenal of effective insecticides decreasing, it is important to consider alternative forms of control. Biotin is an essential coenzyme for insect growth and development. Avidin is a protein found in chicken egg that sequesters biotin and has shown insecticidal properties against a range of insect. We assessed the effectiveness of avidin against the Colorado potato beetle neonates in a no-choice detached leaf bioassay at 0, 17, 34, 51, 102, and 204 microg avidin/ml over 12 d. The LC50 was 136 microg avidin/ml (108-188 95% CL). The combined effects of avidin (136 microg avidin/ml) with Bt-Cry3A or leptines were evaluated with neonates and third instars over 12 and 6 d, respectively. Three potato lines were used: susceptible line, a line engineered to express Cry3A from Bacillus thuringiensis, and a line expressing the natural resistance factor leptines. The addition of avidin at the LC50 concentration significantly reduced consumption by neonates, but it did not affect consumption by third instars feeding on the susceptible line and the leptine line. Survival of neonates feeding on the susceptible line with avidin was significantly reduced compared with the susceptible line. Survival of third instars on the Bt-Cry3A with avidin was significantly reduced after 3 d compared with survival on the Bt-Cry3A, suggesting the addition of avidin may increase susceptibility to Bt-Cry3A.     

The voyage of an invasive species across continents: genetic diversity of North American and European Colorado potato beetle populations

The paradox of successful invading species is that they are likely to be genetically depauperate compared to their source population. This study on Colorado potato beetles is one of the few studies of the genetic consequences of continent-scale invasion in an insect pest. Understanding gene flow, population structure and the potential for rapid evolution in native and invasive populations offers insights both into the dynamics of small populations that become successful invaders and for their management as pests. We used this approach to investigate the invasion of the Colorado potato beetle (Leptinotarsa decemlineata) from North America to Europe. The beetles invaded Europe at the beginning of the 20th century and expanded almost throughout the continent in about 30 years. From the analysis of mitochondrial DNA (mtDNA) and amplified fragment length polymorphism (AFLP) markers, we found the highest genetic diversity in beetle populations from the central United States. The European populations clearly contained only a fraction of the genetic variability observed in North American populations. European populations show a significant reduction at nuclear markers (AFLPs) and are fixed for one mitochondrial haplotype, suggesting a single successful founder event. Despite the high vagility of the species and the reduction of genetic diversity in Europe, we found a similar, high level of population structure and low gene flow among populations on both continents. Founder events during range expansion, agricultural management with crop rotation, and selection due to insecticide applications are most likely the causes partitioning genetic diversity in this species.     

Immunocytochemical localization of peptidergic neurons and neurosecretory cells in the neuro-endocrine system of the Colorado potato beetle with antisera to vertebrate regulatory peptides

A large number of antisera to regulatory vertebrate peptides was tested immunocytochemically on the nervous system of the Colorado potato beetle to further characterize the peptidergic cells of the neuro-endocrine system and to reveal cells participating in endocrine control mechanisms. Neurons, neurosecretory cells, axons and axon terminals were revealed by antisera to ACTH, gastrin, CCK, alpha-endorphin, beta-endorphin, gamma 1-MSH, insulin, motilin, human calcitonin, growth hormone, somatostatin, CRF, ovine prolactin and rat prolactin. Together with previously described results these findings demonstrate that at least 19 different peptidergic cell types are present in the Colorado potato beetle. Several of these cell types are identical with the known neurosecretory cells, while others have not been identified before. The functions of the immunoreactive neurons are as yet unclear, although in two cases the localization of these cells gives some clues. Thus the lateral neurosecretory cells, which are immunoreactive with antisera to beta-endorphin and ovine prolactin, may regulate corpus allatum activity, whereas a CRF immunoreactive substance seems to be used as neurotransmitter by antennal receptors. These immunocytochemical findings do not imply that the immunoreactive substances are evolutionarily related to the vertebrate peptides to which the antisera were raised. It is postulated that if the part of the substance recognized by a certain antiserum is functionally important for the insect, which should be so if the insect peptide is evolutionarily related to its vertebrate homologue, the antiserum should reveal homologous cells in different insect species. The consequence of this hypothesis is, that if an antiserum does not reveal homologous neurons in different insect species, the immunologically demonstrated substance is probably of little physiological importance, and will not be related evolutionarily to the vertebrate analogue. The positive immunocytochemical results in the Colorado potato beetle are discussed in relation to these considerations.     

A hybrid Bacillus thuringiensis delta-endotoxin gives resistance against a coleopteran and a lepidopteran pest in transgenic potato

Expression of Bacillus thuringiensis delta-endotoxins has proven to be a successful strategy for obtaining insect resistance in transgenic plants. Drawbacks of expression of a single resistance gene are the limited target spectrum and the potential for rapid adaptation of the pest. Hybrid toxins with a wider target spectrum in combination with existing toxins may be used as tool to mitigate these problems. In this study, Desiree potato plants were genetically modified to resist attack by insect species belonging to the orders Coleoptera and Lepidoptera, through the insertion of such a hybrid gene, SN19. Transgenic plants were shown to be resistant against Colorado potato beetle larvae and adults, potato tuber moth larvae, and European corn borer larvae. These are the first transgenic plants resistant to pests belonging to two different insect orders. In addition, the target receptor recognition of this hybrid protein is expected to be different from Cry proteins currently in use for these pests. This makes it a useful tool for resistance management strategies.     

NewLeaf Plus® Russet Burbank potatoes: replicase-mediated resistance to potato leafroll virus

Potato leafroll poleovirus and the Colorado potato beetle (Leptinotarsa decemlineata (Say)) are major pests of potato in the USA. The US Department of Agriculture estimates that over 50% of annual insecticide use on potato is applied to control the Colorado potato beetle and aphids that transmit potato leafroll virus (PLRV). To address this issue, Russet Burbank potatoes have been genetically modified for a high level of resistance to infection and the resulting disease symptoms caused by PLRV and to feeding damage caused by the Colorado potato beetle. This resistance was achieved by the expression of the unmodified full-length replicase gene of PLRV and the cry3A insect control protein gene from Bacillus thuringiensis var. tenebrionis. Plant expression constructs containing various modifications of the PLRV replicase gene were produced during the development of this product. The genes in these constructs were a full-length unmodified replicase (open reading frame 2a/2b), an antisense orientation of the full-length cDNA, an open reading frame 1 translation of the full-length gene, and a gene truncation containing the 3 sense coding portion of the replicase gene. Growth chamber experiments demonstrated that transformation of plants with the full-length and 3 sense coding constructs substantially protected these potato plants from infection and disease symptoms caused by PLRV. The Russet Burbank potato expressing the full-length PLV replicase gene and the cry3A gene is a new potato product from NatureMark called NewLeaf Plus®.     

Evaluation of natural and engineered resistance mechanisms in potato against Colorado potato beetle in a no-choice field study

The Colorado potato beetle, Leptinotarsa decemlineata Say, is the major insect pest of potato, Solanum tuberosum L., in eastern North America and is renowned for resistance development, currently resistant to >40 insecticides worldwide. Host plant resistance may assist in delaying in resistance development to insecticides. We evaluated natural host plant resistance mechanisms (glandular trichomes and Solanum chacoense Bitter-derived resistance) and engineered resistance mechanisms (Bacillus thuringiensis [Bt] Berliner cry3A and cry1Ia1) in a no-choice cage study. Six different potato lines representing four host plant resistance mechanisms were evaluated over 2 yr. Egg masses were placed in each cage (one egg mass per plant). Almost no feeding was observed in the Bt-cry3A lines, and only minor feeding was observed in the Bt-cry1Ia1 lines in either year. On the S. chacoense-derived line, there was significantly less defoliation than on either the susceptible line or the glandular trichome line in 2003. In 2004, there was significantly higher defoliation on the S. chacoense-derived line than on the susceptible line or glandular trichome line. The defoliation of the Solanum chacoense-derived line was largely due to larvae clipping the petioles, rather than consumption of the leaves. Defoliation on the glandular trichome line did not differ significantly from the defoliation of the susceptible line, suggesting glandular trichomes may not be effective in controlling larvae and preventing defoliation. This study suggested that Bt can provide high levels of resistance, but the natural resistance mechanisms tested here are variable for control of Colorado potato beetle larvae in no-choice situations.     

In vitro rearing of Edovum puttleri,an egg parasitoid of the Colorado potato beetle,on artificial diets: Effects of insect cell line‐conditioned medium

Effects of conditioned media prepared from cell lines derived from 11 insect species (six families, three orders) on the in vitro growth and development of the egg parasitoid Edovum puttleri were investigated. The parasitoid exhibited significantly different responses to the various insect cell line‐conditioned media that were incorporated into the artificial diets. When cell lines were derived from embryos, higher percentages of 3rd instars and prepupae were observed than when cell lines were derived from fat body or ovaries. Medium conditioned with cell line IPLB‐CPB2 derived from the embryos of the Colorado potato beetle produced the best result. Preconditioning time was important. In general, 5 days of preconditioning appeared to be optimal. The growth‐ and development‐promoting effect may have resulted from growth factors or growth‐supporting factors produced/ released by the insect cell lines into the culture medium. Upon storage at 0–4°C for 7–14 days, the ability of cell line‐conditioned medium to promote development beyond the second instar was greatly reduced (approximately 10–55%). Our studies demonstrated that to support the in vitro growth and development of E. puttleri, insect hemolymph could be successfully replaced with insect cell line‐conditioned medium. These findings should facilitate the development of a cost‐effective mass‐rearing system for E. puttleri and/or other parasitoids. Arch. Insect Biochem. Physiol. 40:173–182, 1999. Published 1999 Wiley‐Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

Inhibitor of apoptosis is an effective target gene for RNAi-mediated control of Colorado potato beetle,Leptinotarsa decemlineata

The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is one of the most notorious and difficult to control pests of potato and other solanaceous crops in North America. This insect has evolved a remarkable ability to detoxify both plant and synthetic toxins, allowing it to feed on solanaceous plants containing toxic alkaloids and to develop resistance to synthetic chemicals used for its control. RNA interference (RNAi) is a natural mechanism that evolved as an immune response to double-stranded RNA (dsRNA) viruses where dsRNA triggers silencing of target gene expression. RNAi is being developed as a method to control CPB. Here, we evaluated four CPB-specific genes to identify targets for RNAi-mediated control of this insect. Out of the four dsRNAs evaluated in CPB larvae and adults, dsIAP (dsRNA targeting inhibitor of apoptosis, iap gene) performed better than dsActin, dsHSP70, and dsDynamin in inducing larval mortality. However, in adults, the mortality induced by dsActin is significantly higher than the mortality induced by dsIAP, dsHSP70, and dsDynamin. Interestingly, a combination of dsIAP and dsActin performed better than either dsIAP or dsActin alone by inducing feeding inhibition in 24 hr and mortality in 48 hr in larvae. When the dsIAP and dsActin were expressed in the Escherichia coli HT115 strain and applied as a heat-killed bacterial spray on potato plants, it protected the plants from CPB damage. These studies show that the combination of dsIAP and dsActin shows promise as an insecticide to control CPB.     

Colorado potato beetle larvae on potato plants expressing a locust proteinase inhibitor

The natural defence system of plants often involves inhibitors of digestive enzymes of their pests. Modem and environmental-friendly methods try to increase this plant resistance by expressing heterologous protease inhibitors in crops. Here we report the effects of expressing a gene from desert locust (Schistocerca gregaria) encoding two serine protease inhibitors in potato on Colorado potato beetle (Leptinotarsa decemlineata) larvae. The gene encoding both peptides on a single chain was used for Agrobacterium-mediated transformation of potato plants. The presence of the active inhibitor protein in the leaves was verified. The feeding bioassays in the laboratory showed that despite the low level of the peptide in leaves, CPB larvae on transgenic plants have grown slightly but significantly more slowly than those on control potato plants. The results support the notion that expression of multifunctional proteinase inhibitors of insect origin in plants might be a good strategy to improve insect resistance.     

危害茄科蔬菜的外来入侵害虫——马铃薯甲虫

马铃薯甲虫是世界著名的入侵害虫,是我国的重要检疫性有害生物,主要危害马铃薯、茄子和西红柿等茄科蔬菜。该甲虫目前分布于美洲、欧洲和亚洲等30多个国家和地区,于1993年入侵我国新疆,到2010年扩散到36个县市,最前沿为木垒县。该文介绍了马铃薯甲虫的扩散历史、危害情况、发生规律以及防治措施,指出我国在西北方向遭受新疆马铃薯甲虫入侵内地威胁的同时,也在东北方向遭受俄罗斯滨海边区马铃薯甲虫对黑龙江及东北地区入侵的严重威胁,应加强防范。     

Pymetrozine causes a nontarget pest, the Colorado potato beetle (Coleoptera: Chrysomelidae), to leave potato plants

Pymetrozine is a selective insecticide that targets aphids. Published assessments of the effects of pymetrozine on nontarget organisms focus mainly on predatory insects, and they rarely indicate toxicity. In a laboratory bioassay, survival of Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), larvae was not affected by pymetrozine exposure. We subsequently used pymetrozine to implement low-aphid-density treatments in a field experiment that involved separate manipulations of Colorado potato beetle density. Unexpectedly, the addition of Colorado potato beetle adults and eggs did not increase the densities of Colorado potato beetle larvae in plots that were sprayed with pymetrozine (applied with water and an adjuvant). In control plots sprayed with water and adjuvant (without pymetrozine), addition of Colorado potato beetles increased densities of their larvae. Data collected on a smaller scale suggest that a behavioral mechanism underlies the population-level pattern: Colorado potato beetle larvae become more active and are less likely to remain on a host plant after exposure to pymetrozine. Thus, potato, Solanum tuberosum L., growers who use pymetrozine against aphids also might benefit in terms of Colorado potato beetle control.     

Novel Bacillus thuringiensis insecticidal crystal protein with a silent activity against coleopteran larvae.

A novel Bacillus thuringiensis crystal protein with a silent activity against the Colorado potato beetle is described. The crystal proteins are produced as bipyramidal crystals. These crystals contain a protein of 129 kDa with a trypsin-resistant core fragment of 72 kDa. Neither a spore-crystal mixture nor in vitro-solubilized crystals are toxic to any of several Lepidoptera and Coleoptera species tested. In contrast, a trypsin-treated solution containing the 72-kDa tryptic core fragment of the protoxin is highly toxic to Colorado potato beetle larvae. The crystal protein-encoding gene was cloned and sequenced. The inferred amino acid sequence of the putative toxic fragment has 37, 32, and 33% homology to the CryIIIA, CryIIIB, and CryIIID toxins, respectively. Interestingly, the 501 C-terminal amino acids show 41 to 48% amino acid identity with corresponding C-terminal amino acid sequences of other crystal proteins. Because of the toxicity of the fragment to the Colorado potato beetle and because of the distinct similarities of the toxic fragment with the other CryIII proteins, this gene was given a new subclass name (cryIIIC) within the CryIII class of coleopteran-active crystal proteins. CryIIIC represents the first example of a crystal protein with a silent activity towards coleopteran insect larvae. Natural CryIIIC crystals are not toxic. Toxicity is revealed only after an in vitro solubilization and activation step.     

基于GIS的马铃薯甲虫扩散与河流关系研究——以新疆沙湾县为例

马铃薯甲虫是一种重要的外来入侵害虫,自1993年传入我国新疆北部地区以来,迅速扩散传播,对我国马铃薯等茄科作物生产造成严重威胁。为明确马铃薯甲虫传播扩散与河流等生态因子之间的关系,结合马铃薯甲虫虫情调查,利用地理信息系统(GIS)的空间分析功能,对新疆沙湾县马铃薯甲虫发生与河流的关系进行研究。结果表明:在沙湾县内,马铃薯甲虫扩散方向与河流流向基本一致,均呈由南向北方向;不同缓冲区内,马铃薯甲虫危害级别差异极显著,缓冲区危害级别从大到小依次:缓冲区2(1-2 km)>缓冲区4(3-4 km)>缓冲区5(4-5 km)>缓冲区1(0-1 km)>缓冲区3(2-3 km);不同河流流域内马铃薯甲虫危害级别也差异极显著,危害级别排序依次是:金沟河>安集海河>玛纳斯河>西岸大渠。     

Effect of crop rotation distance on populations of Colorado potato beetle (Coleoptera: Chrysomelidae): development of areawide Colorado potato beetle pest management strategies

The Colorado potato beetle, Leptinotarsa decemlineata (Say), overwinters adjacent to field edges and infests nearby fields in the spring, primarily by walking. Crop rotation is known to be an effective cultural control against Colorado potato beetle populations limiting spring infestations. Spatial separation is an important consideration in optimizing the rotational effect because long-distance rotations have been shown to reduce Colorado potato beetle infestations. To determine the effect of long-distance rotations on Colorado potato beetle populations in commercial Wisconsin potato production, a geographic area of >18,200 ha (>45,000) acres in southern Portage County, Wisconsin, was selected as an experimental area for areawide pest management of the Colorado potato beetle. From 1997 to 1999, beetle populations at edges within each potato field in this region were determined by spring and fall field sampling. The rotational distance between current and previous potato fields was measured and analysis was run between the distance and Colorado potato beetle populations. Long-distance rotations of >400 m were an effective cultural control management strategy to limit adult beetle infestations in the spring. This strategy can be optimized when collaborating growers are able to maximize their rotational distances by coordinating their rotational schemes within large areawide, geographic locations. Deploying long-distance rotations within a geographic area over many years would limit Colorado potato beetle populations and could result in a significantly reduced Colorado potato beetle populations entering fields in the spring.     

Predation on Colorado Potato Beetle Eggs by Generalist Predators in Research and Commercial Potato Plantings

Field studies quantified predation on Colorado potato beetle [Leptinotarsa decemlineata(Say)] eggs and determined the relationship between predation and egg mass abundance in research and commercial potato plantings in eastern North Carolina. Predator exclusion experiments were conducted weekly in research plantings. In addition, egg mass density and predation on egg masses were monitored throughout the season in research plots and commercial potato fields. Predation was an important source of mortality for Colorado potato beetle eggs. Survivorship of eggs exposed to predators was consistently, significantly lower than survivorship of eggs protected from predation. Averaged over 2 years, the mean survivorship of eggs protected from predation was 69%, compared with 26% survivorship of eggs exposed to predation. Regression analysis failed to detect any relationship between egg mortality due to predation and egg abundance. These results imply that efforts to reduce Colorado potato beetle populations selectively will not be offset by an according decline in abundance of natural enemies and therefore should be fully compatible with naturally occurring biological control.     

马铃薯甲虫防治技术及其抗药性研究进展

马铃薯甲虫Leptinotarsa decemlineata(Say)是世界上重要的毁灭性检疫害虫。国内外针对马铃薯甲虫的防治技术包括农业及物理防治(与非寄主作物合理倒茬轮作,诱集捕杀等)、生物防治(利用微生物农药和植物活性提取物防治,引进天敌控制)以及化学防治(使用有机磷、氨基甲酸酯、拟除虫菊酯类及其他新型杀虫剂防治)等。马铃薯甲虫对杀虫剂的抗性主要与体内代谢酶系、尤其是多功能氧化酶系活性升高有关;抗性遗传方式多为常染色体控制的不完全隐性遗传。抗性检测技术包括传统生物测定法和基因检测法,后者主要包括固相微型测序、单链构象多态性、双向等位特异PCR扩增等,这些新技术在抗药性监测中将发挥越来越重要的作用。     

Inhibition of insect acetylcholinesterase by the potato glycoalkaloid alpha-chaconine.

Homogenates from several insect species were assayed for inhibition of acetylcholinesterase by the potato glycoalkaloid alpha-chaconine. Colorado potato beetle acetylcholinesterase was up to 150-fold less sensitive than other species tested. Acetylcholinesterase from an insecticide-resistant strain of Colorado potato beetles was more sensitive to inhibition than the susceptible strain. Most insect species tested had inhibitory concentrations causing a 50% reduction in activity in the 5 to 40 microM range. Sensitive insect acetylcholinesterases were similar to mammalian cholinesterases in their response to alpha-chaconine. The results indicate that pesticides and host plant resistance factors may interact at the same target. Changes in the target due to selection pressure from either pesticides or host plant resistance factors could affect the efficacy of both control strategies.     

Flight take-off performance of Colorado potato beetle in relation to potato phenology

The flight take-off frequency of adult Colorado potato beetles, Leptinotarsa decemlineata (Say), from potato plants, Solanum tuberosum L. 'Red Pontiac' at the bloom stage of development was 2.2-2.5-fold that of Colorado potato beetle from plants at the vegetative stage. Tests were conducted in a flight chamber over a period of 3 h. Prefeeding Colorado potato beetles for 48 h on potato plants at the bloom or at the vegetative stage before placing them into the flight chamber resulted in the same significantly higher flight take-off frequency from potato plants at the bloom stage than from plants at the vegetative stage. These results demonstrate that the factor in potato plants in bloom that stimulates the flight take-off of the Colorado potato beetle is independent of the feeding history of the beetles and begins acting only when the beetles are in the presence of the plant. According to these results, the dispersal of adult Colorado potato beetles from potato fields in bloom to younger potato fields with plants at the vegetative stage, previously reported in the literature, is at least partly explained by the effect of plant phenology on the frequency of flight take-off. Results confirm the value of planting potato fields of similar phenology over as wide an area as possible to reduce Colorado potato beetle dispersal between fields. Results also imply that staggering the planting dates of conventional potato refuge areas near Colorado potato beetle transgenic or conventionally resistant potato fields is a sound management practice, because it promotes the movement of wild beetles over to the adjacent younger resistant crops.