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.     

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.     

Banded cucumber beetle (Coleoptera: Chrysomelidae) resistance in romaine lettuce: understanding latex chemistry

Many plants subjected to herbivore damage exude latex, a rich source of biochemicals, which plays important roles in host plant resistance. Our previous studies showed that fresh latex from Valmaine, a resistant cultivar of romaine lettuce Lactuca sativa L., applied to artificial diet is highly deterrent to feeding by banded cucumber beetle, Diabrotica balteata LeConte, compared to the latex of a closely related susceptible cultivar Tall Guzmaine. The deterrent factor(s) could be extracted from Valmaine latex with water–methanol (20:80). In this study, further fractionation of the methanolic crude extract of Valmaine latex was performed using reverse-phase and ion-exchange solid-phase extraction to isolate the deterrent compounds. Retention of deterrent compounds on anion and cation exchange resin suggested the presence of highly polar compounds with both carboxylic and amine groups in Valmaine latex. Further bioassay-directed fractionation of cation exchange extract using LC/MS indicated the presence of at least 3 major and an unknown number of minor compounds in the bioactive fraction between 3 and 4 min. The m/z 210 out of the 3 major compounds showed strong amino acid characteristics (glutamine and/or glutamic acid) when subjected to further MS ⁿ degradation. Our studies suggest that nitrogenous ingredients of latex play a key role in Valmaine resistance to D. balteata, and latex may be a source of bioactive compounds with a potential use in pest management.     

Examining Cuphea as a potential host for western corn rootworm (Coleoptera: Chrysomelidae): larval development

In previous crop rotation research, adult emergence traps placed in plots planted to Cuphea PSR-23 (a selected cross of Cuphea viscosissma Jacq. and Cuphea lanceolata Ait.) caught high numbers of adult western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), suggesting that larvae may have completed development on this broadleaf plant. Because of this observation, a series of greenhouse and field experiments were conducted to test the hypothesis that Cuphea could serve as a host for larval development. Greenhouse-grown plants infested with neonates of a colonized nondiapausing strain of the beetle showed no survival of larvae on Cuphea, although larvae did survive on the positive control (corn, Zea mays L.) and negative control [sorghum, Sorghum bicolor (L.) Moench] plants. Soil samples collected 20 June, 7 July, and 29 July 2005 from field plots planted to Cuphea did not contain rootworm larvae compared with means of 1.28, 0.22, and 0.00 rootworms kg(-1) soil, respectively, for samples collected from plots planted to corn. Emergence traps captured a peak of eight beetles trap(-1) day(-1) from corn plots on 8 July compared with a peak of 0.5 beetle trap(-1) day(-1) on 4 August from Cuphea plots. Even though a few adult beetles were again captured in the emergence traps placed in the Cuphea plots, it is not thought to be the result of successful larval development on Cuphea roots. All the direct evidence reported here supports the conventional belief that rootworm larvae do not survive on broadleaf plants, including Cuphea.     

Egg-hatching synchrony and larval cannibalism in the dock leaf beetle Gastrophysa viridula (Coleoptera: Chrysomelidae)

Females of leaf beetles and many other herbivorous insects lay eggs in coherent batches. Hatchlings emerge more or less simultaneously and often prey on their late-hatching clutchmates. It is not certain, however, whether this synchrony of hatching is a mere by-product of cannibalism or whether an additional synchronizing factor exists. The following simple experiment was aimed at determining the causal relationship between cannibalism and simultaneous larval emergence. Egg clutches of the dock leaf beetle Gastrophysa viridula were split into two halves. These halves were either kept as coherent groups in two separate dishes or, alternatively, only one half remained whole, whereas the other one was divided into single eggs, each of which was incubated in a separate dish. Halving of a clutch into coherent groups only slightly disrupted the synchrony of emergence. The consequence of individual isolation was more dramatic. Half-clutches consisting of disconnected solitary eggs required almost twice as much time for complete emergence of all larvae, which was significantly more than cannibalism as a sole synchronizing factor might explain. Moreover, survival rates were the same in coherent half-clutches (in the presence of cannibalism) and among isolated individuals. This group effect and the small contribution of cannibalism suggest the existence of an additional synchronizing factor. Possible mechanisms underpinning this phenomenon 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.     

Preliminary life table of the spotted tortoise beetle,Aspidomorpha miliaris (Coleoptera: Chrysomelidae) in Sumatra

From December, 1981 to February, 1982, a population study of the spotted tortoise beetle, Aspidomorpha miliaris, feeding on a shrub-like morning glory, Ipomea carnea, was conducted in Padang, Sumatra with the construction of a life table.

1. Dissection of oothecae collected from the field after hatching clarified that the average egg mass size was 43.4 and hatching rate was 25.0%. Causes for egg mortality included: parasitism by a wasp, Tetrastichus sp. A(Europhidae) (49.8% of eggs laid), predation (12.8%), disappearance of egg masses (5.3%) and hatching failure (7.1%). An ant, Dolichoderus bituberculatus, visiting the extrafloral nectaries of the host plnts was responsible for predation and disappearance of the egg masses. The ants again attacked the larvae and pupae.
2. Larvae showed a gregarious habit for almost the entire larval period. Survival rates between two successive instars were low and constant, ranging from 70 to 90%, but only 1.3% of final (5th) instars become pupae (six individuals). Since the growth of host plants was extremely rapid, shortage of food was rare in larval stages. The sudden drop in numbers after 5th instar may be due to predation and/or dispersal of matured larvae from the host plants for pupation.
3. Pupae were attacked by three species of parasitic wasps:Tetrastichus sp. C, Pediobius elasmi (Eulophidae) and Cassidocida aspidomorphae (Tetracampidae). Among the six pupae, two were parasitized, one died of disease and two disappeared. Out of 4078 eggs laid, only one emerged to adult.

     

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.     

Prairie grasses as hosts of the northern corn rootworm (Coleoptera: Chrysomelidae)

We evaluated 27 prairie grass species thought to be among those dominant 200 yr ago in the northern midwest as larval hosts of the northern corn rootworm, Diabrotica barberi Smith and Lawrence. Maize (Zea mays L.), spring wheat (Triticum aestivum L.), and grain sorghum (Sorghum bicolor L.) were included as controls for a total of 30 species. Twenty pots of each species were planted in a randomized complete block design. Each pot was infested 5 wk later with 20 neonate northern corn rootworm larvae. Two pots within each species and block were assigned an extraction date of 7 or 14 d after infestation. The remaining two pots from each block were used to monitor adult emergence. The percentage of larvae recovered, change in larval head capsule width, and change in average dry weights varied significantly among the grass species. The highest percentage of larvae was recovered from slender wheatgrass, Elymus trachycaulus (Link), and this was significantly greater than the percentage recovered from all other species including maize for the 14-d sample date. Several additional species were also relatively good hosts, in that the percentage of larvae recovered from these species was not significantly different from maize. The average dry weight of larvae recovered was significantly greater for larvae recovered from maize than for larvae recovered from all other species except slender wheatgrass, when the two samples dates were combined. Overall, adults were produced from only 6 of the 28 species evaluated, and no analysis was performed because of the low numbers. The results of this study are discussed in relation to the potential of alternate hosts of northern corn rootworm to serve as a bridge to survival on transgenic maize.     

Host-plant effects on larval survival of a salicin-using leaf beetle Chrysomela aeneicollis Schaeffer (Coleoptera: Chrysomelidae)

Several species of willow leaf beetles use hostplant salicin to produce a defensive secretion that consists of salicylaldehyde. Generalist arthropod predators such as ants, ladybird beetles, and spiders are repelled by this secretion. The beetle larvae produce very little secretion when they feed on willows that lack salicylates, and salicin-using beetles prefer salicylate-rich willows over salicylate-poor ones. This preference may exist because the larvae are better defended against natural enemies on salicylate-rich willows. If this is true, the larvae should survive longer on those willows in nature. However, this prediction has not been tested. I determined the larval growth and survival of Chrysomela aeneicollis (Coleoptera: Chrysomelidae) on five willow species (Salix boothi, S. drummondiana, S. geyeriana, S. lutea, and S. orestera). These species differed in their salicylate chemistries and in leaf toughness but not in water content. The water content varied among the individual plants. Larval growth of C. aeneicollis did not differ among the five species in the laboratory, but it varied among the individual plants and it was related to the water content. In the field, C. aeneicollis larvae developed equally rapidly on the salicylate-poor S. lutea and on the salicylate-rich S. orestera. Larval survival was greater on S. orestera than on S. lutea in one year (1986), but there was no difference between them during three succeeding years. In another survivorship experiment, larval survival was low on the medium-salicylate S. geyeriana, but high on the salicylate-poor S. boothi and on S. orestera. Larval survival in the field was related to the larval growth and water content that had been previously measured in the laboratory. These results showed that the predicted relationship between the host plant chemistry and larval survival did not usually exist for C. aeneicollis. One possible reason for this was that the most important natural enemies were specialist predators that were unaffected by the host-derived defensive secretion. One specialist predator, Symmorphus cristatus (Hymenoptera: Eumenidae), probably caused much of the mortality observed in this study. I discuss the importance of other specialist predators to salicin-using leaf beetles.     

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.     

Female's preference for oviposition site and larval performance in the water-lily beetle,Galerucella nymphaeae (Coleoptera: Chrysomelidae)

Water-lily beetles prefer younger rather than older water-lily leaves as oviposition sites. By the time of hatching, however, young leaves have aged consieerably. Larval performance of the water-lily beetle was measured on different types of leaves of the yellow water-lily and compared with oviposition preference of females. The leaf types used in the experiments were categorized as (i) young, (ii) natal (medium-aged) and (iii) old. The natal leaves were the ones on which larvae from a particular egg-batch had hatched. There were two sets of experiments. First, larvae were raised from eggs to pupae on young and on old leaves. Second, the growth of the 1st-instar larvae was measured on young, natal, and old leaves. The development time from egg to pupa did not differ between young and old leaves, but larvae growing on young leaves attained a higher pupal weight. In the second experiment the 1st-instar larvae grew fastest on their natal leaves, but there was also variation in the growth rate of progeny from different egg-batches. Larval growth on young and old leaves did not differ significantly. Larvae tried to emigrate much less from natal than other types of leaves. Females tended to lay eggs on leaves where larval growth was fastest. It seems that medium-aged leaves are best for larval growth, but the leaf characteristics responsible for this remain unresolved.     

A comparison of artificial diets for mass rearing Brontispa longissima (Coleoptera: Chrysomelidae) as hosts for the larval and the pupal parasitoids

The coconut hispine beetle, Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae) is a serious pest of coconut palm. In this study, we developed an artificial diet for B. longissima so that the beetle could be used as a host for rearing two of its parasitoids, Asecodes hispinarum Boucek (Hymenoptera: Eulophidae) and Tetrastichus brontispae Ferrière (Hymenoptera: Eulophidae). The new artificial diet represents an improvement of our previous diet, which we used as a control. When beetle larvae were reared on the new diet, which contains cysteine but not cellulose powder and has twice as much coconut leaf powder as in the control, the adult emergence was 71% (approximately 2 times that in the control). We also examined the suitability of beetles fed on the new diet as hosts for the larval parasitoid A. hispinarum and the pupal parasitoid T. brontispae. The percentage of wasps that emerged from hosts that were fed the new diet was higher than that from the control-fed hosts. The new diet allowed both A. hispinarum and T. brontispae to produce adult wasps of the next generation, whereas the control only allowed T. brontispae to produce the next generation. These results suggest that the new diet is suitable for B. longissima and will facilitate mass-rearing of A. hispinarum and T. brontispae.     

Suitability of some southern and western pines as hosts for the pine shoot beetle, Tomicus piniperda (Coleoptera: Scolytidae)

The pine shoot beetle, Tomicus piniperda (L.), is an exotic pest that has become established in North America. Discovered in Ohio in 1992, it has since been found in at least 13 states and parts of Canada. The beetle can cause significant growth loss in pines, and it represents a potential threat to trees in areas where it has not yet become established. To evaluate this threat to native pines, field and laboratory tests were conducted on several common and important southern and western species to determine whether they are acceptable hosts for T. piniperda. Comparisons with Pinus sylvestris L., Scots pine, a preferred natural host for the beetle, were made where possible. Measurements of beetle attack success on southern pine billets showed that Pinus taeda L., Pinus echinata Miller, Pinus elliottii var. elliottii Engelmann, Pinus palustris Miller, and Pinus virginiana Miller (loblolly, shortleaf, slash, longleaf, and Virginia pine, respectively) and two western pines, Pinus ponderosa Lawson and Pinus contorta Douglas (ponderosa and lodgepole pine, respectively), were acceptable for breeding material, but brood production was highly variable. Among the southern pines, P. taeda and P. echinata were susceptible to shoot feeding by T. piniperda, whereas P. elliottii was highly resistant and P. palustris seemed to be virtually immune. Shoot feeding tests on the western pines were conducted only in the laboratory, but there was moderate-to-good survival of adults feeding on both species. It seems that if T. piniperda is introduced into the south and west it will likely establish and may cause some damage to native pines. P. taeda may be affected more than other southern pines because it is the most abundant species, it is readily attacked for brood production, which can result in moderately large broods, and the beetle survives well during maturation feeding on P. taeda shoots.     

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.     

Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America

Abstract.  1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp.
2. Neonate larval feeding behaviour was quantified on 15 food plant species: 10 from the Liliales, three from the Asparagales and two eudicots. Larvae fed plants closely related to the genus Lilium were more likely to initiate feeding, less likely to abandon their food leaf, and consumed more leaf area.
3. In no-choice tests, females oviposited on the novel hosts Lilium philadelphicum , Medeola virginiana , Clintonia borealis , Streptopus amplexifolius , and Polygonatum biflorum ; however, all but L. philadelphicum received very few eggs. Non- Lilium novel hosts were not used for oviposition when presented along with Asiatic lilies in choice tests.
4. A single individual was reared to the adult stage on the novel host S. amplexifolius . Several larvae survived to the pupal stage on M. virginiana , although no adults emerged from those pupae. Larvae reared on the native wood lily L. philadelphicum performed equally well or better than on the Asiatic cultivar.
5. Our results indicate that the lily leaf beetle poses a threat to native Liliaceae. Several native Lilium species, including L. philadelphicum , are threatened or endangered in certain jurisdictions throughout their range; these species should be monitored closely for colonisation by the beetle.     

Interactions over time between cereal leaf beetle (Coleoptera: Chrysomelidae) and larval parasitoid Tetrastichus julis (Hymenoptera: Eulophidae) in Utah

The phenology of parasitism of the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae) by Tetrastichus julis (Walker) (Hymenoptera: Eulophidae) was studied in small grain fields from 2000 to 2005 in northern Utah, after release and redistribution of the partially bivoltine larval parasitoid during the 1990s. Host larvae first occurred in May, with peak infestation typically occurring in early to mid-June. Parasitism by overwintering females of T. julis was highest among earliest developing beetle larvae. Thereafter, rates of parasitism fell to low levels (5-10% or less) by the latter half of June, when heat accumulation had reached 280-350 degree-days (based on a minimum threshold of 8.9 degrees C). With the emergence of second generation parasitoids, rates of parasitism rose to levels approaching 100% among the relatively few late-developing larvae of O. inelanopus. Clear and consistent differences over the years were not observed among different crops of small grains (barley, wheat, or oats) either in the phenology and intensity of beetle infestation, or in the rate of parasitism of beetle larvae. The rate of parasitism was especially high in 2005, and an increase in the minimum level of parasitism (observed each year at mid-season) was apparent over the course of the study. These results indicate that the parasitoid has become well established and seems to be continuing to increase in its impact on O. melanopus in northern Utah, despite a relatively hostile environment of crop management, wherein most fields are plowed and disked annually.     

Influence of western corn rootworm (Coleoptera: Chrysomelidae) larval injury on yield of different types of maize

Two field experiments were conducted in 1995-1996 to determine if there are common yield responses among maize hybrids to larval western corn rootworm, Diabrotica virgifera virgifera LeConte injury. Three yellow dent hybrids, five white food grade dent hybrids, and a popcorn hybrid were included in the study. The minimum level of rootworm injury as measured by root damage ratings (3.2-4.2) that significantly reduced yield was similar across the hybrids included in the study. However, the pattern of yield response to different rootworm injury levels varied among hybrids. This suggests that maize hybrids may inherently differ in their ability to tolerate rootworm injury and partition biomass in response to injury and other stresses. The complex interaction among hybrid, level of injury, and other stresses suggests that a common western corn rootworm injury-yield relationship may not exist within maize.     

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.