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.     

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.     

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.     

Survey of Colorado potato beetle insecticide resistance in Idaho

Colorado potato beetle populations from Idaho were surveyed for resistance to carbofuran, endosulfan, esfenvalerate, and phosmet in a discriminating concentation bioassay of spring emergent and first generation adults. No carbofuran or endosulfan resistance was detected in 29 populations surveyed. Esfenvalerate and phosmet resistance was detected in all potato growing areas of the state. For the same populations, spring adults were more sensitive to phosmet than were first generation adults. Susceptible populations were found in the same regions as resistant populations.     

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.     

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.     

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.     

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.     

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.     

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).     

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.     

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.     

A plastic-lining trenching device for the control of Colorado potato beetle: Beetle Excluder

An apparatus was developed to dig a trench and line it with plastic as a means of controlling the Colorado potato beetle. The apparatus was based on the concept of a plastic mulch laying device used by the market garden industry. The plastic lined trenches were “V” shaped in configuration with an average width at the top of 740 ±17 mm and a depth of 223±12 mm. Controlled experiments under field conditions demonstrated that trenches produced by the “Beetle Excluder” retained 95% of the beetles trapped. The trenches survived the weathering of a full season without requiring any maintenance.     

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.     

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.     

Progress report: Resistance to the Colorado potato beetle and potato leafhopper inSolanum tuberosum subsp.andigena

An extensive collection of 1527 clones ofS. tuberosum subsp.andigena was screened in 1973 in unreplicated plots to test for resistance to the Colorado potato beetle and potato leafhopper. All clones were susceptible to the beetle. Of 17 clones selected in the 1973 tests for resistance to the potato leafhopper, 7 selections were significantly more resistant than the control (Katahdin) in a replicated experiment in 1974.