Resistance to adult banded cucumber beetle (Coleoptera: Chrysomelidae) in romaine lettuce

Four cultivars of lettuce, Lactuca sativa L., were evaluated for their resistance to the adult banded cucumber beetle, Diabrotica balteata LeConte, under laboratory conditions. When paired with each of the other three cultivars, leaf consumption in all possible combinations of short-term (48 h) two-choice tests among the cultivars was significantly reduced only for 'Valmaine'. However, in a 48-h no-choice situation, beetles fed Valmaine or 'Short Guzmaine' had similarly low leaf consumption, followed by 'Parris White', with the greatest consumption occurring on 'Tall Guzmaine'. In longer term experiments, female beetles fed Valmaine for 10, 13, or 16 d generally had lower survival and the lowest body weights compared with beetles fed any of the other three cultivars. No mature eggs were found in the ovaries of females fed Valmaine, whereas from 14% (Short Guzmaine, day 10) to 100% (Tall Guzmaine, day 13) of females fed the other cultivars produced mature eggs. In a starvation test, most D. balteata of either sex did not survive after 7 d with access only to water. Moreover, starved females did not produce mature eggs. Thus, food consumption by adult D. balteata is very important to their survival and reproductive performance, and it is likely that females fed Valmaine failed to produce mature eggs because they did not consume a sufficient amount of this cultivar. However, because Valmaine-fed beetles maintained their body weight and lived significantly longer than starved beetles, it appears that they can obtain some nourishment from their limited feeding on this cultivar. Overall, these results suggest that Valmaine, and to a lesser extent short Guzmaine (a cultivar produced by crossing Valmaine with two other cultivars), exhibit antixenosis-based resistance against D. balteata.     

Male traits under cryptic female choice in the spotted cucumber beetle (Coleoptera: Chrysomelidae)

Males of the spotted cucumber beetle (Diabrotica undecimpunctata howardi) rhythmically stroke females with their antennae during copulation. Males that stroke quickly have a higher probabilityof being accepted as a mate. We determined (1) the mechanismby which females prevent unattractive males from passing spermatophores,(2) whether antennal stroking signals to females the likelihoodof receiving a nuptial gift, and (3) if other male traits inaddition to stroking are subjected to sexual selection fromfemale preference. Dissections of pairs flash-frozen in copuladuring and after antennal stroking showed musculature that,when contracted, folded the vaginal duct leading to the female'sbursa copulatrix in a way that prevented complete penetrationby the aedeagus. These muscles were always contracted whilemales were stroking and always relaxed after stroking had ceased.Males accepted as mates did not differ from males that failedto pass a spermatophore in either absolute or relative bodyweight, aedeagus length, or the amount of cucurbitacins (potentialnuptial gifts) sequestered in their spermatophores. Although99% of the beetles that came to cucurbitacin-rich Cucurbitafruits in the field were males, males that had sequestered cucurbitacins did not stroke females faster than males withno cucurbitacins, and fast-stroking males were not more likelyto find and sequester cucurbitacins than were males that strokedmore slowly. Males with a cucurbitacin slurry painted on theirantennae had no mating advantage over controls. We concludethat females discriminate among males after copulation hasbegun on the basis of antennal stroking displays (or some traitcorrelated with stroking speed) that males perform to enticefemales to relax their bursal sphincter.     

Potential resistance of crape myrtle cultivars to flea beetle (Coleoptera: Chrysomelidae) and Japanese beetle (Coleoptera: Scarabaeidae) damage

Field and laboratory studies were conducted to identify potential resistance among crape myrtles, Lagerstroemia spp., to Japanese beetle, Popillia japonica Newman and to flea beetles, Altica spp. Damage ratings revealed variation among cultivars in susceptibility to beetle feeding. Cultivars with Lagerstroemia fauriei Koehne in their parentage exhibited the least amount of damage in choice and no-choice experiments, with few exceptions. The data indicate that both beetle species cause more feeding damage on certain cultivars of Lagerstroemia indica L., such as 'Country Red', 'Twilight', and 'Carolina Beauty' than interspecific cultivars with L. fauriei in their parentage, such as 'Natchez', 'Tonto', and 'Muskogee'. When comparing the effect of parentage on all of the major pests of crape myrtle, L. faurei confers resistance to all pests except crape myrtle aphid. No correlation was found between leaf toughness, leaf color, and leaf nutrients in estimating flea beetle cultivar preference. With this information, growers can more effectively target scouting measures to the most susceptible cultivars. and breeders can select plants that will require the fewest chemical inputs.     

Field and vegetable crops as hosts of larval western spotted cucumber beetle (Coleoptera: Chrysomelidae)

The western spotted cucumber beetle, Diabrotica undecimpunctata undecimpunctata Mannerheim, is an important pest of melons (Cucurmis melo L.) in northern California. Recent observations indicate that adults are using alfalfa (Medicago sativa L.) as a feeding host and larvae may be developing on the roots. Greenhouse studies were conducted during the winters of 2009 and 2010 in which larval development was compared on the roots of six field and vegetable crops commonly grown in the southern Sacramento Valley. The growth parameters used to evaluate the hosts were larval and pupal head capsule width, body width, and body length as well as total survival percentage and survival percentage to the third instar. According to larval growth and survivorship in 2009, maize (Zea mays L.) was the best host, followed by alfalfa and tomato (Solanum lycopersicum L.) that were roughly equivalent to one another. Melon was a slightly weaker host than alfalfa and tomato; sunflower (Helianthus annuus L.) was a completely incompatible host and thus dropped from the 2010 study. In 2010, melon was the weakest host for larval development. Maize was the superior host again followed closely by alfalfa that performed slightly better than tomato and lima bean (Phaseolus lunatus L.). Data suggest that larval western spotted cucumber beetles may primarily develop outside of melon fields and the adults emigrate to melons.     

An alternative sampling technique for cucumber beetles (Coleoptera: Chrysomelidae) and diurnal beetle activity on muskmelon

Field studies were conducted to investigate the effectiveness of yellow sticky traps as an alternative sampling technique for striped, Acalymma vittatum (F.), and spotted, Diabrotica undecimpunctata howardi Barber, cucumber beetles (Coleoptera: Chrysomelidae) and the diurnal beetle activity on muskmelon, Cucumis melo L., near Vincennes, IN, in 2003 and 2004. The experimental design included six replications of seven 20-m-long rows each of muskmelon with 1.5 m between rows. On each sampling date, two yellow sticky traps were placed randomly between rows in each replication. One sticky trap was placed vertically with the lower edge even with the top of the canopy, whereas the other trap was placed horizontally, even with the top of the canopy. After traps were placed in the field, number of beetles on plants was counted in situ from 0800 to 1600 hours at 2-h intervals the next day. After 48 h in the field, the number of cucumber beetles adhering on traps was counted. Analyses of variance and Tukey's multiple comparison procedure were used to compare the densities of beetles among sampling times, and regression analyses were applied to correlate the numbers of beetles on traps and the numbers of in situ counts. Results show that both species of cucumber beetles were most active from 1200 to 1400 hours, and 20 beetles on the vertically positioned sticky trap were equivalent to one beetle per plant in the field. The application of the sampling technique and scouting time for cucumber beetle management are discussed.     

Yield response of pumpkin and winter squash to simulated cucumber beetle (Coleoptera: Chrysomelidae) feeding injury

Field studies were conducted to characterize the yield responses of pumpkin, Cucurbita pepo L., and wintersquash, Cucurbita maxima Duch., to simulated striped cucumber beetle, Acalymma vittatum (F.), feeding damage. Preliminary studies in pumpkin ('Spookie') were conducted in 1993, and more complete studies in 1994 and 1995 in pumpkin (Spookie), and in 1995 and 1996 in winter squash ('Waltham'). Plants were artificially injured 1 time at the cotyledon, 1st, 2nd, or 3rd true leaf stages by clipping specified percentages of leaf area from all leaves on the plant. Treatments consisted of a control treatment with no simulated injury and 4 levels of simulated injury. Pumpkin treatments were 10, 20, 40, and 80% leaf area removal in 1993 and 1994 and 20, 40, 60, and 80% in 1995. Winter squash treatments were 20, 40, 60, and 80% leaf area removal in 1995, and 10, 20, 40, and 80% in 1996. In 1993, 5 wk after planting, mean leaf, stem, and total dry weight were significantly lower on pumpkin plants subjected to > or = 20% simulated leaf injury regardless of the growth stage when the injury occurred. Injury at the 3rd leaf stage resulted in a significant reduction in the mean leaf and total dry weight of plant, across all levels of injury. At 2-3 wk before crop maturity, fruit weight and number of fruit per plant were significantly lower with 80% leaf area removal. In 1994 and 1995, and when pumpkins were grown to full maturity and apparently able to compensate for the simulated damage, neither number nor weight of marketable fruit per plant were affected significantly by simulated injury at any stage of development nor level of simulated injury. In contrast, > or = 20% and 80% leaf area removal to winter squash resulted in significant reductions in the weight of marketable fruit and/or number of marketable fruit, in 1995 and 1996, respectively. The results of this study indicate that pumpkins can tolerate relatively high levels of simulated defoliation, whereas winter squash is less tolerant. Variable results across years in winter squash may indicate an interaction between injury and plant stress caused by abiotic factors such as soil moisture availability.     

Inheritance and synergism of resistance to imidacloprid in the Colorado potato beetle (Coleoptera: Chrysomelidae)

Colorado potato beetle, Leptinotarsa decemlineata (Say), adults and larvae collected from Long Island, NY, were 100.8 and 13.2 times more resistant to imidacloprid, respectively, compared with a susceptible strain. This high level of resistance appeared in only the third field season of imidacloprid use. Analysis of probit lines from F1 reciprocal crosses indicated that resistance to imidacloprid in adults was inherited autosomaly as an incompletely recessive factor. The degree of dominance of the resistance was -0.23 and -0.10, respectively, 3 and 7 d after treatment (incompletely recessive). The chi2 analysis of response ratio statistics from F1 x susceptible back crosses compared with a monogenic model suggested that more than one locus is responsible for resistance to imidacloprid. Synergism studies with piperonyl butoxide suggested that mixed-function oxidase mediated detoxification is responsible for the resistance to imidacloprid in adults. Synergism studies with S,S,S-tributyl phosphorotrithioate (DEF) indicated that esterase mediated detoxification may be an additional resistance factor. Mixed-function oxidase mediated detoxification is probably also one of the mechanisms of resistance to imidacloprid in larvae. Because the synergists used did not completely eliminate resistance in the resistant strain, there may be additional mechanisms involved. Refugia and crop rotation decrease the frequency of homozygous resistant genotypes and may be effective resistance management strategies, because of the recessive nature of the resistance.     

Evaluation of cucurbitacin-based gustatory stimulant to facilitate cucumber beetle (Coleoptera: Chrysomelidae) management with foliar insecticides in melons

The bitter plant-derived compounds cucurbitacins are known to stimulate feeding of adult cucumber beetles (Coleoptera: Chrysomelidae). A cucurbitacin-based gustatory stimulant applied as a flowable bait combined with either spinosad or carbaryl was compared with foliar sprays of spinosad and carbaryl for controlling two cucumber beetle species (Diabrotica undecimpunctata undecimpunctata Mannerheim and Acalymma trivittatum Mannerheim) in honeydew melons (Cucumis melo L.). Field studies were conducted on the University of California-Davis plant pathology farm in 2008 and 2009. Beetle densities after applications and fruit damage from beetle feeding were compared among treatments. In addition, beetle survival was compared within field cages placed over the treated foliage infested with beetles. Using all three measures of efficacy, we determined that the addition of cucurbitacin bait had no effect on the level of cucumber beetle control with carbaryl in either 2008 or 2009. In both years, spinosad did not significantly reduce cucumber beetle densities in either field cages or field plots and did not reduce fruit damage relative to the untreated control. The addition of the bait to spinosad did not improve its efficacy. A laboratory bioassay of the spinosad formulation used in the field showed it had significant lethal effects on adults of both cucumber beetle species. Results indicated that the bait formulation used did not improve cucumber beetle control but may benefit from the addition of floral attractants or using a different type of cucurbitacin.     

Baseline susceptibility to imidacloprid and cross resistance patterns in Colorado potato beetle (Coleoptera: Chrysomelidae) populations

During 1995-1998, we tested 134 geographically discrete populations of Colorado potato beetle, Leptinotarsa decemlineata (Say), from the United States, Canada, Germany, France, and Poland for susceptibility to imidacloprid. Neonates were assayed on potato-based agar diet incorporated with imidacloprid and exposed on filter paper to esfenvalerate, azinphosmethyl, and carbofuran to characterize cross-resistance. In all 4 yr, Long Island populations were the most tolerant to imidacloprid, with LC50s ranging up to 29 times higher than the most susceptible populations. Responses to imidacloprid did not change significantly on farms where populations were assayed over time, except for those from Long Island, which doubled in overall tolerance to imidacloprid since 1995. Much of this tolerance was already present before imidacloprid was used on Long Island. Correlative analysis of the populations tested over the 4 yr indicated positive cross-resistance patterns with esfenvalerate and azinphosmethyl. This response was probably caused by preexisting metabolic and excretion mechanisms selected by previous exposure. There was no significant pattern of cross-resistance with carbofuran or bensultap. Regression slopes were also significantly negatively correlated with LC50 values for imidacloprid, indicating higher heterogeneity, which could lead in further resistance development. We discuss the relative sensitivity of diet-incorporated assays with neonates compared with other bioassay studies. Based on a pooled group of susceptible populations tested in 1995, a baseline LC50 of 0.39 ppm and a discriminating concentration of 8 ppm were suggested to detect early stages of resistance in "suspect" populations. We also suggest application strategies for imidacloprid that reduce selection pressure.     

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.     

Spatial distribution of the cereal leaf beetle (Coleoptera: Chrysomelidae) in wheat

A 2-yr study was conducted in wheat fields in South Carolina involving weekly sampling of cereal leaf beetle, Oulema melanopus (L.). In each of the six fields of this study, temporal patterns showed two distinct peaks in March and in May of adult O. melanopus. Populations decreased as wheat plants matured. In 2009, larval populations had one peak in April in between the two adult peaks. The χ(2) statistics for observed and Poisson predicted distributions of O. melanopus indicated nonrandom distribution for adults and larvae. In addition, the values of I(D) were >1 for adults and larvae in both years across sampling dates. These results indicate that the sampling distributions of both adult and larval populations of O. melanopus were aggregated. Slopes of Taylor power's law (b) and patchiness regressions (β) were significantly (P < 0.05) different than one in all cases, except for b in 2008 for adults. Across sampling dates, the distance from field border had a significant effect on adult O. melanopus in both years, but not on larval O. melanopus. Densities of adult O. melanopus were greatest at 0 m (the field edge), and decreased at 5-25 m from the field edge. The inverted distance weighted interpolation method showed considerable levels of spatial variability in densities within fields. High densities along the edge of wheat fields suggests that localized control methods in wheat may be effective in reducing migration of O. melanopus and damage in corn, Zea mays L.     

Quantitative trait locus mapping of pyrethroid resistance in Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

Quantitative trait locus (QTL) mapping is a valuable new tool for locating genomic regions that underlie variation in important traits such as insecticide resistance. Because QTL mapping complements a candidate gene strategy for understanding the genetic architecture of important traits, it may also facilitate the identification of genes causing important variation. After mapping the QTL locations, markers closely linked to QTL can be used for genetic analysis of population structure and to measure the spread and increase of resistance-causing QTL alleles. In this study, QTL influencing resistance to the pyrethroid insecticide esfenvalerate were mapped in the Colorado potato beetle Leptinotarsa decemlineata (Say) (CPB). Three QTL contributing to esfenvalerate resistance were identified from a mapping population of 79 individuals analyzed at 90 marker loci. One QTL had a large effect and two QTL had smaller effects. The major QTL occurs on the X chromosome, overlapping the position of a candidate gene (Leptinotarsa decemlineata Voltage sensitive sodium channel [LdVssc1]) previously implicated in pyrethroid resistance. Resistance-increasing alleles at the two minor-effect QTL originated with the susceptible parent, suggesting that alleles of small effect may be segregating in susceptible populations. Comparison of the New York population from which the susceptible parent originated with a more-susceptible population from North Carolina suggests that the minor-effect loci identified here may explain some of the variation in tolerance observed among susceptible populations. DNA sequencing of a portion of LdVssc1 shows that the resistance-conferring allele from the resistant parent does not contain the kdr mutation previously found in CPB and typically observed in other insects that are resistant to pyrethroid insecticides because of changes in this gene.     

Ovipositional biology of Viburnum leaf beetle, Pyrrhalta viburni (Coleoptera: Chrysomelidae)

Pyrrhalta viburni Paykull, a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. We measured lifetime oviposition capacity of mated and unmated females reared in the laboratory versus field-collected females, as well as ovipositional response to physical characteristics of the host plant. Both mated and unmated females produced eggs, but at different rates. Field-collected females and mated females reared in the laboratory laid similar numbers of egg masses containing similar numbers of eggs, but unmated females laid approximately one half as many eggs, the result primarily of smaller clutch size. Mated females reared in the laboratory had a preovipositional period of 11.4 +/- 1.7 versus 29 + 11.7 d for unmated females, and unmated females lived significantly longer than mated females. The angle and diameter of stems of V. trilobum, a very susceptible host, both greatly influenced oviposition; females laid most eggs on vertically oriented stems, and those of smallest diameter; when these factors were combined, stem diameter predominated. Females also had a very strong geotactic response, preferring to lay eggs on portions of stems toward gravity, even when stems were at fairly shallow angles.     

Genotypic variability and mode of action of Colorado potato beetle (Coleoptera: Chrysomelidae) resistance in seven Solanum species

Accessions from seven wild Solanum species were evaluated in the field for resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say). The multivariate insect population density data were analyzed using factor analysis. The factors extracted corresponded to relevant phases of the insect's life cycle and provided information on the mode of resistance (antixenosis and antibiosis) of the plant species. S. berthaultii, S. capsicibaccatum, S. jamesii, S. pinnatisectum, and S. trifidum demonstrated both antixenosis and antibiosis but expressed different levels of resistance. The mode of resistance of S. polyadenium seemed to be antibiosis and that of S. tarijense antixenosis. Genetic variability and heritability of insect resistance traits within accessions was trivial or inconsistent for all Solanum species studied.     

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.     

Benefits of polyandry in Parthenium beetle,Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae)

The influence of polyandry on the reproductive performance of females and on offspring fitness in Zygogramma bicolorata Pallister was investigated using four experimental treatments, viz. (A) monandrous, limited mating, (B) monandrous, unlimited mating, (C) polyandrous, no-choice limited mating, and (D) polyandrous, mate choice unlimited mating. Polyandrous females had higher reproductive performance than monandrous ones. Monandrous females subjected to unlimited matings had higher egg viability than those subjected to limited matings, but fecundity did not differ significantly. In polyandrous females, the freedom to choose mates did not affect reproductive performance. However, offspring of polyandrous females allowed mate choice developed fastest and had the highest survival at 25, 27, and 30 °C. Thus, polyandry in Z. bicolorata appears to provide both direct (material) and indirect (genetic) benefits resulting in better reproductive performance and increased adaptability of the offspring to counter environmental stresses. The present study not only adds to the knowledge of reproductive biology of Z. bicolorata but it could also be of economic value as it may help in the mass rearing of Z. bicolorata and in the management of Parthenium hysterophorus.     

Endemism patterns in the Italian leaf beetle fauna (Coleoptera,Chrysomelidae)

In this contribution the results of a zoogeographical analysis, carried out on the 123 endemic leaf beetle species (Coleoptera: Chrysomelidae) occurring in Italy and its immediately adjacent regions, are reported. To assess the level of faunistic similarity among the different geographic regions studied, a cluster analysis was performed, based on the endemic component. This was done by calculating the Baroni Urbani & Buser’s similarity index (BUB). Finally, a parsimony analysis of endemicity (PAE) was used to identify the most important areas of endemism in Italy.     

Mating behavior of the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Abstract  Circadian mating rhythms, mating frequency, mating duration, and the effect of mating duration on fecundity and fertility in the cabbage beetle, Colaphellus bowringi were investigated in the laboratory. Mating occurred throughout the 24-h cycle but the majority of copulations occurred in the photophase with two apparent peaks, one at 8:00 and another at 16:00. Mating frequency observations for 10 consecutive days indicated that pre-mating period of C. bowringi was about 4 days, and pairs mated an average of 5 times per day and an average of 40 times during the first 10 days. There was a negative correlation between mating frequency and mating duration during the consecutive mating. The mean duration of the first copulation (136.24 ± 4.62 min) was significantly longer than those of the second (57.87 ± 2.03 min), third (53.05 ± 2.05 min) and fourth copulation (30.86 ± 2.98 min). Fecundity showed a slight increase with increasing mating duration but no significant difference among treatments. However, fertility was significantly influenced by the mating duration in this species. Mating of 20-min duration did not produce viable eggs. The mean percentage of fertile eggs with completed mating duration (204.43 ± 18.96 min, 56.75% fertile eggs) was significantly higher than those with 60 min (39.55%) and 30 min (17.91%) mating duration, suggesting that the longer mating duration might be associated with transfer of more sperm that are used to increase the fertility of eggs.     

Romaine lettuce latex deters feeding of banded cucumber beetle: a vehicle for deployment of biochemical defenses

Latex is widely found among plant species and is known to play a defensive role against certain herbivores. Two romaine lettuce, Lactuca sativa L. (Asteraceae) cultivars, 'Valmaine' (resistant) and 'Tall Guzmaine' (susceptible), were selected to study the potential of latex as a defense mechanism against the banded cucumber beetle, Diabrotica balteata LeConte (Coleoptera: Chrysomelidae). Latex from Valmaine strongly inhibited feeding of adult D. balteata compared to latex from Tall Guzmaine when applied to the surface of artificial diet. Beetles consumed significantly less diet from disks treated with Valmaine latex than they consumed from diet treated with Tall Guzmaine latex, in both choice and no-choice tests. In a choice test involving diet disks treated with Valmaine latex from young leaves vs. disks treated with latex from mature leaves, the beetles consumed significantly less diet treated with latex from young leaves. No significant difference in diet consumption was found between diets treated with latex from young and mature leaves of Tall Guzmaine in choice tests. Three solvents of differing polarity (water, methanol, and methylene chloride) were tested to extract deterrent compounds from latex; Valmaine latex extracted with water:methanol (20:80) strongly inhibited beetle feeding when applied to the surface of artificial diet. In no-choice tests, fewer beetles were observed feeding on diet treated with water:methanol (20:80) extract of Valmaine latex than on diet treated with a similar extract of Tall Guzmaine latex, resulting in significantly less consumption of the diet treated with the Valmaine latex extract. These studies suggest that moderately polar chemicals within latex may account for resistance in Valmaine to D. balteata.     

Host plant choice experiments of Colorado potato beetle (Coleoptera: Chrysomelidae) in Virginia

Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.