ScreeningSolanum germplasm for resistance to Colorado potato beetle

TuberousSolanum accessions were screened for resistance to Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say), in terms of CPB-caused defoliation in field trials with natural infestations of CPB. Cluster and multivariate discriminant analyses were used to distinguish among species and accessions. Several highly CPB-resistant and relatively homogeneous accessions were identified.     

Susceptibility of Idaho populations of Colorado potato beetle to four classes of insecticides

A laboratory study was conducted in 1984 to establish base-line data on insecticide tolerance and to detect incipient resistance to representative insecticides within the four major classes of insecticides that are used to control Colorado potato beetles in Idaho. Insecticides tested were aldicarb (a carbamate), endosulfan and DDT (chlorinated hydrocarbons), azinphosmethyl and disulfoton (organophosphates) and fenvalerate (a pyrethroid). Compared with results obtained elsewhere, Idaho populations of Colorado potato beetle proved relatively susceptible to the insecticides tested. However, significant differences were detected among sample populations indicating the potential for insecticide resistance exists.     

Colorado potato beetle resistance management strategies for transgenic potatoes

NewLeaf potatoes could provide substantial ecological and economic benefits to potato growers. A concern with NewLeaf potatoes, however, is that Colorado potato beetle may develop resistance to the Bt endotoxin because of the intense selection pressure imposed by its constant presence in the transgenic crop. Before these cultivars were released, however, entomologists throughout North America conducted biological research needed for a strategy to prevent or delay resistance in Colorado potato beetle. This paper describes the considerations and research behind the proposed strategy. Because NewLeaf potatoes express a relatively constant and high concentration of Bt endotoxin throughout the foliage of each plant, reducing selection for resistance must come from planting standard potatoes as a refuge for susceptible beetles. Avoiding resistance through random mixtures of NewLeaf and standard potatoes was evaluated in laboratory and field studies. The conclusion from this research was that the seed mixture would not provide an effective refuge. The most effective alternative refuge was judged to be a block of standard potatoes planted in the same field as the NewLeaf potatoes. By allowing susceptible beetles to survive in their fields, potato growers might sustain the benefits of very effective controls.     

Field selection for esfenvalerate resistance by the Colorado potato beetle

Five insecticide application regimes were evaluated for two years to determine their influence on the development of esfenvalerate resistance by the Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say). These included sequential applications of esfenvalerate; two alternated uses of esfenvalerate, azinphosmethyl, endosulfan, oxamyl, andBacillus thuringiensis or cryolite; an IPM program; and one early season esfenvalerate application. Both CPB adults and first instars were tested for esfenvalerate resistance before and after insecticide applications. The LC₅₀’s in the early 1992 season were correlated with values in the late 1991 season. However, over the winter, esfenvalerate resistance of CPB adults decreased, but was relatively stable for first instars. Esfenvalerate LC₅₀’s late in the season were generally higher than values early in the season. Increases in esfenvalerate LC₅₀’s were correlated with the number of esfenvalerate applications made in these fields during the growing season, with the greatest increase found in the sequential esfenvalerate treatment.     

Fine screeningSolanum (potato) germplasm accessions for resistance to Colorado potato beetle

This study was conducted to investigate the utility of systematic screening at the genotype level withinSolanum accessions highly resistant to the Colorado potato beetle. Evaluations of clonally replicated genotypes showed that most accessions reported to be uniform when screened as populations contained small but significant variation among genotypes for resistance to oviposition, larvae, and defoliation, differences for numbers of larvae being most common. Adult counts and percentage defoliation were not as useful in evaluating among-genotype variability in beetle resistance. Genotypes ofS. pinnatisectum WRF 343 andS. tarijense PI 473227 were the most uniformly and highly resistant to Colorado potato beetle. Genotypes of S.berthaultii PI 473331,S. chacoense PI 473405, andS. tarijense PI 473336 were moderately to highly resistant, and genotypes ofS. bukasovii PI 473494 andS. canasense PI 230511 were uniformly susceptible to Colorado potato beetle. Nonparametric correlation analyses indicated that number of egg masses, small larvae, large larvae, and defoliation scores were positively correlated, negatively correlated, or not correlated, depending on the species. One generation of selection attempting to segregate resistance and susceptibility in nearly uniform and highly resistantS. pinnatisectum WRF 343 resulted in “divergent” populations that could not be distinguished from each other or the base population. Thus, through genotype (“fine”) screening and selection, we showed that some existing populations are virtually pure for extreme resistance. Use of individuals from such families would make screening breeding populations more efficient, and reduce the risk of losing resistance genes that have non-dominant effects. Fine screening, recurrent selection, and maintenance of such elite populations is recommended as an extension of population-based evaluation usually done by genebanks.     

Glycoalkaloids and resistance to the Colorado potato beetle inSolanum chacoense Bitter

Resistance of 20 F₂ Solarium chacoense Bitter clones to the Colorado potato beetle,Leptinotarsa decemlineata (Say), was measured in a field test. Levels of total glycoalkaloids (TGA) and composición of the glycoalkaloid mixtures in foliage of the clones were also determined. Clones with either commersonine or dehydrocommersonine as the major foliar glycoalkaloid were significantly more resistant (lower damage ratings, fewer larvae and adult insects) than clones with solanine and chaconine. Damage ratings were negatively correlated (r = -0.67, p = 0.01) with foliar TGA levels. The results indicate that the types of glycoalkaloids present in the foliage ofS. chacoense may be as important as the level of TGA in limiting damage and numbers of insects.     

Suspension velocity of the Colorado potato beetle in free fall

The suspension velocity of the Colorado potato beetle was determined for four stages of its life cycle. Suspension velocities measured using an experimental video technique agreed reasonably well with theoretical values. Suspension velocities for the adults, fourth, third, and second instars were 9.4, 9.5, 7.3, and 5.9 m/sec, respectively. Recent experimental results suggest that a large percentage of adults and large larvae of the Colorado potato beetle are missed during a single pass of commercial field scale vacuum insect collectors. The relatively low suspension velocity of free falling small larvae explain, at least in part, why only 3% of the small larvae fell to the ground.     

Control of the Colorado potato beetle by treatment of potato seed pieces

Dusting or soaking freshly cut potato seed pieces in systemic insecticides controlled the first generation larvae of the Colorado potato beetle at Yakima, Washington in 1970. The most promising materials were tested again in a larger experiment in 1971. Fifty days after treatment, Bay 37344 (4-(methylthio)-3,5,xylyl methylcarbamate), Dasanit^® (O,O-diethyl-O-[p-(methylsulfinyl) phenyl] phosphorothioate), Shell SD 17250 (N-(methylcarbamoyl)oxy]thioacetimidic acid ester with 3-mercaptopropionitrile) and Plant Protection PP062 (dimethylamino)-4,5,6-dimethyl pyrimidinyl dimethylcarbamate) all gave significantly better control of the larvae than methomyl, azinphosmethyl and menazon.     

Control of the Colorado potato beetle withBacillus thuringiensis varietyThuringiensis

Field tests were conducted to determine the effectiveness of an experimental preparation ofBacillus thuringiensis var.thuringiensis against Colorado potato beetle infestations on potatoes and tomatoes. Applications were made weekly with a tractor-towed commercial sprayer at the rates of either 473, 946, or 2,838 ml. ofB.t.t. in 378.41 of water per 0.4 hectare. Significant reductions were observed in treated plots of all stages of the beetle. All untreated plants were completely defoliated by the end of the test due to beetle feeding. No significant differences were observed among the different treatment levels.     

ND2858-1: A useful source of resistance to the Colorado potato beetle

This paper describes a new source of host-plant resistance to the Colorado Potato Beetle (CPB;Leptinotarsa decemlineata (Say)) in a tetraploid potato (Solanum tuberosum L.) selection, ND2858-1. This hybrid was recorded as a cross betweenS. fendleri ssp.fendleri (A. Gray) and NDSU selection ND1215-1. Field defoliation of this and progeny clones from a subsequent cross to an cultivar was reduced by 50% to 90% in open-choice field screening plots. Progeny of ND2858-1 are vigorous, with high yield potential, and some clones have tuber glycoalkaloid content equivalent to commercial cultivars. These clones are male and female fertile and may be useful to other potato breeding programs. Further characterization of this resistance source is in progress.     

An on-farm insecticide resistance test kit for colorado potato beetle (Coleoptera: chrysomelidae)

Test kits were developed to enable growers to assess insecticide resistance in Colorado potato beetle populations. Kits included tests for resistance to: carbofuran (Furadan® 4F), phosmet (Imidan® 50WP), esfenvalerate (Asana® 1.9EC), and a combination of esfenvalerate & piperonyl butoxide (Butacide® 8EC). Tests were petri dishes containing filter paper treated with a discriminating concentration of insecticide (i.e., kills susceptible beetles but not resistant beetles). Discriminating concentrations were determined by testing susceptible and resistant strains of beetle across a range of insecticide concentration. About 200 test kits were distributed during the summer of 1988. Results received indicate: 1) Michigan beetle populations were either susceptible or highly resistant to carbofuran, 2) phosmet resistance was more widespread than previously thought, 3) many populations showed moderate to high levels of resistance to esfenvalerate, and 4) adding piperonyl butoxide reduced resistance to esfenvalerate, in many, but not all populations. Resistance kits help growers determine if insecticide resistance is present in beetle populations (either prior to or after an insecticide application), and also generate data useful to research and extension personnel in documenting the extent and distribution of resistance.     

Influence of Colorado potato beetle sample counts and plant defoliation on potato tuber production

Field experiments were designed to subject Superior potato plants to various levels of defoliation by the Colorado potato beetle (CPB)Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae. Defoliation occurred during each of five consecutive plant growth periods and CPB population, plant leaf area, and tuber weight data were recorded for each period. A visual defoliation rating scheme provided an accurate estimate of actual potato plant leaf area of defoliated plants. Data generated from regression analysis demonstrated a significant dependence of leaf area on CPB numbers per plant during some plant growth periods, but numbers of CPB accounted for very little of the total variation in tuber weight. Plant leaf area was the most important independent variable in the tuber weight regression model.     

Management of the Colorado potato beetle using the entomogenous fungusBeauveria bassiana

Small field plots of Katahdin potatoes on Long Island, NY were treated 6 times in 1980 for control of Colorado potato beetle (CPB)Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae, using either the entomogenous fungusBeauveria bassiana (Balsamo) Vuill. (Bb) at 5x 10¹³ colony forming units/ha or fenvalerate at 0.227 kg active ingredient/ha. No significant differences were found between Bb and fenvalerate treatments in egg mass size and viability or in the total foliage consumed by first generation CPBs. First generation CPB larval populations were significantly higher in Bb plots. Oviposition by first generation adults and second generation beetle populations were higher in fenvalerate plots. Average yield was 29.4 metric tons/ha in fenvalerate plots and 24.6 metric tons/ha in Bb plots (a 16% reduction), but nearby untreated plots were completely defoliated by July 24 and yielded <7 metric tons/ha (> 60% reduction).     

Assessing fungicide resistance in populations of Alternaria in Idaho potato fields

Early blight, caused by the fungus Alternaria solani and brown leaf spot, caused by Alternaria alternata, are important diseases of potato crops in Idaho. In recent years growers have reported a reduction in efficacy of fungicides traditionally used in the past decade to control early blight. In 2009, a collection of A. solani 39 isolates were screened for resistance to azoxystrobin, pyraclostrobin, boscalid and famoxadone. Fungicide sensitivity testing was done using spiral plate dilution gradients. Results showed that of 39 isolates screened, all were resistant to azoxystrobin and three were resistant to boscalid. None were resistant to pyraclostrobin or famoxadone. In summer 2010, more isolates were collected (9 A. alternata and 26 A. solani) and the survey was expanded to include more fungicides with four different modes of action that targeted succinate dehydrogenase (SDH), methionine biosynthesis, mitochondrial respiration and multi-site contact activity. New isolates of A. solani and A. alternata were also collected from two additional sites. The results showed that 57% of the isolates were resistant to boscalid as well as an average of 63% of the isolates being resistant to the strobilurin fungicides. Seven and 15% of isolates were resistant to penthiopyrad (an SDH inhibitor), and pyrimethanil (a methionine biosynthesis inhibitor), respectively. However, none of the isolates were resistant to fluopyram (an SDH inhibitor) or a mixture of fluopyram and pyrimethanil. Although there appears to be cross resistance developing in Alternaria spp. to some of the new SDH inhibitors like penthiopyrad, others such as fluopyram are still showing limited to no resistance development in Alternaria spp. in Idaho.     

The effect of light intensity on Colorado potato beetle resistance and foliar glycoalkaloid concentration of fourSolanum chacoense clones

Controlled environment experiments were used to determine the effect of light intensity on levels of glycoalkaloids and resistance to the Colorado potato beetle (CPB),Leptinotarsa decemlineata Say, inSolanum chacoense Bitter clones that synthesized acetylated glycoalkaloids, the leptines. Plants were grown under two light intensities, 50 or 250 ?mol m^-2S^-1, and bioassayed for CPB resistance by placing neonate larvae on excised foliage. Larval development stage and mortality were recorded after four days. The leptine-synthesizing clones responded to the increase in light intensity with a 2–4 fold increase in level of foliar leptines. Larval development rate on foliage from plants grown under high light intensity was reduced and larval mortality increased. Results showed a significant (p>0.05) effect of light on glycoalkaloid synthesis and CPB resistance.     

The germplasm release of NYL 235–4, a clone with resistance to the Colorado potato beetle

Clones selected from the wild diploid species,Solanum berthaultii, have been shown to possess valuable levels of resistance to the Colorado potato beetle (Leptinotarsa decemlineata), as well as to insects such as aphids, flea beetles, leafhoppers and the potato tuber moth. Resistance is associated with the presence of glandular trichomes on the foliage ofS. berthaultii (2). Six generations after producing a hybrid between the diploid species and a tetraploid variety, a clone with good beetle and leafhopper resistance, as well as reasonable agronomic characteristics has been produced.     

Bacillus thuringiensis a potential control agent for the Colorado potato beetle

In laboratory tests conducted to determine the effectiveness of the exotoxin ofBacillus thuringiensis against the Colorado potato beetle,Leptinotarsa decemlineata (Say), applications sprayed on tomato foliage at dilutions ranging from 10^?1 through 10^?4 killed 90% of the 1st and 2nd stage beetle larvae. As the dosage decreased, the time to achieve this level of mortality increased from 4 to 9 days. Adult beetles were not killed by these treatments; however they did cease feeding. In field tests, the highest dosages ofB. t. sprayed on either tomato or potato plants provided adequate or nearly complete protection when applied weekly. Young larvae that ingested sub-lethal doses developed into adults with atrophied mouthparts and antennae, transformations of the paired parts of the labial palps into an unpaired part, the appearance of a tarsal-like claw on a palp, and malformation of the cranial sclerities.     

The flowering tobacco as a new alternative host for the Colorado potato beetle

The potential of the flowering tobacco,Nicotiana alata, to sustain the survival and the development of the Colorado potato beetle (CPB) was assessed. We made food preference, larval development and rearing tests in relation with other plant species, specially with potato. In spite of a clear preference of the CPB for potato, the insects could complete a full life cycle on the flowering tobacco. In comparison with CPBs on potato, those on the flowering tobacco had a slight delay of two days in their development, beginning when larvae reached their tenth day. CPBs on the flowering tobacco had a much lower survival rate (14.0% against 66.7%) and adults were smaller (100.9 mg against 133.0 mg). Nevertheless, the flowering tobacco is the firstNicotiana species which is an acceptable alternative host for the CPB, and could facilitate the survival and the distribution of the insect.