Genetic Structure of Populations of the Colorado Potato Beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The genetic structure of a Colorado potato beetle population from Kiev oblast was examined by cluster analysis of individual RAPD patterns. The obtained clustering indicates that the population is structured. This may be explained by adaptation to pyrethroid insecticides used for controlling the population size of this pest. Microevolutionary factors affecting the genetic structure of local populations of Colorado potato beetle are discussed.     

Potato field colonization by low-density populations of Colorado potato beetle as a function of crop rotation distance

Monitoring of 10 and 12 commercial potato, Solanum tuberosum L., fields in 2004 and 2005, respectively, confirmed for a low-density population of Colorado potato beetle, Leptinotarsa decemlineata (Say), that potato fields nearest to the previous year's potato fields are significantly more colonized by this beetle than more distant fields. This pattern is partially explained by the presence of a reservoir of colonizers estimated at 35% of the season-long colonizing population in 2004 and 2005. These beetles, which emerged before potato plants broke the ground, were ready to establish themselves on nearby potato plants. The colonizing Colorado potato beetles dispersed within the maximum range of 1.5 km over a season, and the colonization risk for the new crop decreased with distance from the previous year's crop. There was no evidence that rotation distance delayed colonization. In terms of pest management, although the findings confirm that only long 1.5-km rotations can prevent Colorado potato beetle colonization, they also demonstrate that short rotations of 100 m or more can make substantial contributions to pest management programs for low-density beetle populations.     

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.     

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.     

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.     

Differential predation by Coleomegilla maculata on Colorado potato beetle strains that vary in growth on tomato

This study tests the hypothesis that the generalist predator Coleomegilla maculata DeGeer causes differential mortality of Colorado potato beetle, Leptinotarsa decemlineata (Say), larvae differing in their degree of genetic adaptation to tomato (Lycopersicon esculentum Mill.) as a host plant. Results of a series of laboratory experiments demonstrate that adult C. maculata can cause higher mortality to nonadapted than adapted Colorado potato beetle larvae. The extent of differential mortality caused by C. maculata depended on age of potato beetle larvae; presence of potato beetle eggs; whether or not the predator had a choice among prey items; and, in choice situations, the ratio of adapted to nonadapted potato beetle larvae. Although adult C. maculata have the potential to prey differentially on tomato-adapted and nonadapted Colorado potato beetle larvae in mixed populations, the magnitude of differential predation in a natural setting could be highly variable.     

Characterization of intra-population genetic polymorphism of the Colorado potato beetle using ISSR-markers and phenotypes

The level of genetic diversity was estimated in a local population of Colorado potato beetle using ISSR-markers and specific pronotum patterns. In contrast to the unchanged level of diversity in ISSR, Shannon's diversity index calculated on the base of pronotum pattern variants was decreasing during summer testifying adaptivity of that sign. The results also show the difference in the level of genetic diversity of females comparing to males.     

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.     

非寄主植物间套作对马铃薯甲虫种群及其天敌的影响

农田作物布局作为害虫生态调控的重要内容,一直是保护性生物防治的研究热点。为进一步明确马铃薯田块作物间套作种植模式对马铃薯甲虫种群动态的影响,探索马铃薯甲虫可持续防控的新思路与新方法,本研究在马铃薯甲虫发生期对马铃薯-玉米、马铃薯-向日葵、马铃薯单作3种作物间套作模式进行田间种群数量调查,分析比较不同种植模式下的马铃薯甲虫种群动态差异。结果表明：在马铃薯甲虫发生期,马铃薯单作第二代幼虫为害高峰期出现晚于两种间套作模式,第一代成虫为害高峰期早于两种间套作模式。第二代幼虫为害低峰期（8月26日-9月7日）时,马铃薯-玉米间套作幼虫量显著低于马铃薯单作（P<0.05）,马铃薯-玉米间套作幼虫量显著低于马铃薯-向日葵（P<0.05）,整个调查期间,马铃薯单作虫量要大于两种间套作。此外,天敌昆虫群落调查表明：间套作玉米异色瓢虫量显著高于马铃薯单作（P<0.05）,间套作向日葵的草蛉、食蚜蝇虫量高于马铃薯单作。间套作向日葵或玉米对越冬代马铃薯甲虫的扩散有影响,马铃薯播种初期间套作向日葵或玉米能在一定程度上阻隔马铃薯甲虫的定殖扩散。     

Local variation in susceptibility of Colorado potato beetle (Coleoptera: Chrysomelidae) to insecticide

The susceptibility status of Colorado potato beetle, Leptinotarsa decemlineata (Say), adults to phosalone was determined by dip and glass jar assay techniques. Bioassay results indicated a narrow variation in Colorado potato beetle insecticide susceptibility among sample sites. LC50 values were generally highest from specimens collected in field that received frequent phosalone applications for seven consecutive growing seasons. In five populations tested, LC50 values ranged from 503.72 to 827.95 ppm in dip test method. In glass jar technique, resistance ratio value of 1.72 for LC50 was obtained. A significant linear relationship between LC50 values of individual populations across test methods was detected. Both bioassay techniques were suitable for monitoring resistance to insecticide in Colorado potato beetle adult populations. Glass jar technique, however, exhibited less variability in LC50 estimates and showed a higher degree of sensitivity than the dip method. Filter paper and leaf disk techniques for larvae were two bioassay methods used to determine phosalone susceptibility in L. decemlineata populations. Both bioassay techniques exhibited a similar level of susceptibility of the larvae to phosalone; however, the fiducial limit values from filter paper method were narrow than the leaf disk assay technique. A significant direct relationship between LC50 values of individual population across test methods was observed. Differences in LC50 ranking among fields between adults and larvae indicated a differential susceptibility to insecticide between life stages. Low LC50 values obtained from Colorado potato beetle in sample sites indicated that phosalone resistance was not severe in these fields. The glass jar and filter paper testing methods are simple and sensitive test techniques for measuring susceptibility of Colorado potato beetle adults and larvae to phosalone, respectively.     

不同寄主植物上马铃薯甲虫种群生长发育的比较研究

马铃薯甲虫Leptinotarsa decemlineata (Say)是马铃薯Solanum tuberosum等茄科作物上的一种毁灭性害虫。为了探明寄主植物对新疆马铃薯甲虫种群生长发育的影响, 本研究通过非选择性试验测定了马铃薯、 茄子Solanum melongena和番茄Lycopersicon esculentum 3种栽培寄主及野生寄主中亚天仙子Hyoscyamus pusillus对马铃薯甲虫种群生长发育、 存活、 繁殖及生命表参数的影响。结果表明： 马铃薯甲虫幼虫虽然能够取食番茄, 但幼虫的发育历期长、 存活率低且蛹不能羽化, 表明番茄不是新疆马铃薯甲虫种群的适宜寄主。马铃薯、 茄子、 中亚天仙子3种寄主植物对该虫卵、 幼虫、 蛹的存活率和发育历期及成虫产卵前期没有显著影响, 但对蛹重和繁殖力影响显著。取食不同寄主植物后, 该虫蛹重和繁殖力从大到小的次序为： 马铃薯＞茄子＞中亚天仙子; 种群的净增殖率(R₀)、 内禀增长率(r_m)和种群趋势指数(I)从大到小依次为： 马铃薯＞茄子＞中亚天仙子。因此马铃薯为新疆马铃薯甲虫种群的最适宜寄主, 其次为茄子和中亚天仙子, 而番茄为不适宜寄主。     

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.     

Enzymatic systems of insecticide detoxication in a population of Colorado beetles resistant to permethrin

The activity of enzymes providing for permetrin detoxication in the imago resistant natural population of the Colorado potato beetle Leptinotarsa decemlineata was studied with the view of elucidating the biochemical mechanisms of resistance to the insecticide. It was demonstrated that the activity of the main enzymes of insect detoxication, i.e., microsomal monooxygenases, nonspecific esterases and glutathione-S-transferases in the permetrin-resistant population of L-decemlineata is enhanced as compared with the permetrin-sensitive population. It was demonstrated that the inhibitors of microsomal monooxygenases, piperonyl butoxide, and of nonspecific esterases, butifos, significantly increase the sensitivity of the resistant population to permetrin. The experimental results suggest that the activity of microsomal monooxygenases and nonspecific esterases is the main factor which determines the resistance of the Colorado potato beetle to permetrin.     

Individual polymorphism by RAPD markers in spring generation of the Colorado beetle Leptinotarsa decemlineata (Say)]

Genetic diversity of Colorado potato beetle in a natural population from Fastovskii rayon, Kiev oblast was estimated using RAPD. The level of polymorphism for RAPD markers was far higher in the spring generation than in the sample obtained from the same locality in summer of the preceding year. The frequency of individual RAPD markers was found to differ in males and females of potato beetle.     

Individual Polymorphism for RAPD Markers in Spring Generation of Colorado Potato Beetle Leptinotarsa decemlineata(Say)

Genetic diversity of Colorado potato beetle in a natural population from Fastovskii rayon, Kiev oblast was estimated using RAPD. The level of polymorphism for RAPD markers was far higher in the spring generation than in the sample obtained from the same locality in summer of the preceding year. The frequency of individual RAPD markers was found to differ in males and females of potato beetle.     

A freeze-dried diet to test pathogens of Colorado potato beetle

The Colorado potato beetle is an important pest on potato, eggplant, and tomato. Because Colorado potato beetles develop resistance to insecticides quickly, new methods are needed for control. Bacillus thuringiensis is the only bacterium to successfully control Colorado potato beetle. Until recently, one of the drawbacks to testing bacteria against the Colorado potato beetle has been the lack of an artificial diet for screening. Previous artificial diets will only be consumed by Colorado potato beetle larvae when fresh. To improve storage, we developed a freeze-dried diet, based on a 96-well plate, suitable to feed larvae for the duration of a bioassay. Individual diet components were tested both for their effect on insect growth and on pathogen toxicity. When the preservatives, methylparaben and sorbic acid, were removed from the diet, the average weight of second instar larvae increased from 7.9 mg to greater than 9.8 mg. The preservatives inhibited the growth of two of the bacteria tested, Photorhabdus luminescens HM and Chromobacterium sp. PRAA. The removal of these preservatives also allowed for fungal growth and reduced survival from 94 to 38%. Removing diet preservatives, that inhibited the growth of Chromobacterium sp. PRAA, increased the total mortality of the larvae as well as reducing the time needed to kill 50% of the larvae. Compared to incorporation of bacteria into molten diet, the total mortality of Colorado potato beetle fed either P. luminescens HM or Chromobacterium sp. PRAA on freeze-dried diet doubled. Preparation of freeze-dried diet need not be synchronized with the insect or the pathogen. The freeze-dried diet gave consistent results as measured by low control mortality and pathogen toxicity over time.     

Two new bacterial pathogens of Colorado potato beetle Coleoptera: Chrysomelidae)

Other than Bacillus thuringiensis Berliner, few bacteria are lethal to the Colorado potato beetle (Leptinotarsa decemlineata [Say]), a major pest of potatoes and eggplant. Expanded use of biologicals for the control of Colorado potato beetle will improve resistance management, reduce pesticide use, and produce novel compounds for potential use in transgenic plants. Using freeze-dried, rehydrated artificial diet in pellet form to screen bacteria lethal to other insects, we determined that strains of Photorhabdus luminescens killed Colorado potato beetle larvae. The LC50 for second instar larvae of strain HM5-1 was 6.4 +/- 1.87 x 10(7) cells per diet pellet. In an attempt to find additional naturally occurring P. luminescens strains toxic to Colorado potato beetle larvae, we recovered, from soil, bacteria that produced a purple pigment. This bacterial strain, identified as Chromobacterium sp. by 16S ribosomal DNA sequencing, was also toxic to Colorado potato beetle larvae within 3 d. The LC50 for second instar larvae for these bacteria was 2.0 +/- 0.79 x 10(8) cells per diet pellet, while the LC50 was approximately 1 log lower for third instar larvae. P. luminescens appeared to kill by means of a protein toxin that may be similar to the described lepidopteran protein toxins. Based on the heat and acid stability, the toxin or toxins that Chromobacterium sp. produces, while not fully characterized, do not appear to be typical proteins. In both bacteria, the toxins are made after exponential growth ceases.     

Diverse enzymatic specificities of digestive proteases, 'intestains', enable Colorado potato beetle larvae to counteract the potato defence mechanism

In response to insect attack, high levels of proteinase inhibitors are synthesised in potato leaves. This can cause inefficient protein digestion in insects, leading to reduced growth, delayed development and lower fecundity. It has been suggested that Colorado potato beetle overcomes this defence mechanism by inducing the production of a set of cysteine proteases that are resistant to potato proteinase inhibitors. Experiments with gut extracts showed that these proteases have unusual inhibition profiles as they are not inhibited by most of the cystatins but are strongly inhibited by thyropins. In this study we have isolated three cysteine proteases from adapted guts of Colorado potato beetle larvae, named intestains 1, 2 and 3, the first cysteine proteases known to be involved in extracellular protein digestion. The N-terminal sequences suggest their classification into the papain family. Intestains differ in substrate specificities and inhibitory profiles. Their substrate specificities suggest that intestains 1 and 2 are general digestive enzymes, while intestain 3 has a more specific function. The inhibitory profile of intestain 1 is similar to that of proteases of the papain family. However, the Ki values for the interaction of intestain 2 with the same set of inhibitors are several hundred fold higher, which would enable the enzyme to circumvent the potato defence mechanism characterised by high concentrations of protease inhibitors in attacked potato leaves. A further, different strategy of the Colorado potato beetle to avoid potato defence is exhibited by intestain 3, which is able to cleave off the N-terminus of model cystatin and thus inactivate the inhibitor. These results suggest that the Colorado potato beetle combines different strategies to counteract plant defence mechanisms.     

Impact of Bacillus thuringiensis – insecticides on population dynamics and egg predation of the Colorado potato beetle in North Carolina potato plantings

Field studies to assess the impact of Bacillus thuringiensis var. tenebrionis (Btt)-insecticides on Colorado potato beetle populations, egg survivorship and levels of predation on egg masses were conducted in replicated field research plots during two years. Stage-specific abundance of the Colorado potato beetle and predation on egg masses were monitored in Btt-treated and untreated potato plots in both years. The Btt-treatments significantly reduced densities of large (third and fourth instar) Colorado potato beetle larvae. The densities of large larvae remained below 0.5 and 3 per plant in the Btt-treatment while peak densities of 4.5 and 21 large larvae per plant occurred in the untreated control in 1992 and 1993, respectively. Regular sampling of egg masses indicated that predation rates in Btt-treated and untreated plots did not differ significantly although, in 1993, predation rates of up to 100% were recorded, only in Btt-treated plots. In a predator exclusion study carried out in 1992, survivorship of protected eggs was consistently higher than of eggs exposed to predation. Seasonal survivorship of exposed eggs was significantly lower in the Btt-treated than in untreated plots. Btt insecticides for control of Colorado potato beetles provided direct protection of the crop and were compatible with naturally-occurring biological control of Colorado potato beetle eggs due to predation.