Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans

Folivorous insect responses to elevated CO₂-grown tree species may be complicated by phytochemical changes as leaves age. For example, young expanding leaves in tree species may be less affected by enriched CO₂-alterations in leaf phytochemistry than older mature leaves due to shorter exposure times to elevated CO₂ atmospheres. This, in turn, could result in different effects on early vs. late instar larvae of herbivorous insects. To address this, seedlings of white oak (Quercus alba L.), grown in open-top chambers under ambient and elevated CO₂, were fed to two important early spring feeding herbivores; gypsy moth (Lymantria dispar L.), and forest tent caterpillar (Malacosoma disstria Hübner). Young, expanding leaves were presented to early instar larvae, and older fully expanded or mature leaves to late instar larvae. Young leaves had significantly lower leaf nitrogen content and significantly higher total nonstructural carbohydrate:nitrogen ratio as plant CO₂ concentration rose, while nonstructural carbohydrates and total carbon-based phenolics were unaffected by plant CO₂ treatment. These phytochemical changes contributed to a significant reduction in the growth rate of early instar gypsy moth larvae, while growth rates of forest tent caterpillar were unaffected. The differences in insect responses were attributed to an increase in the nitrogen utilization efficiency (NUE) of early instar forest tent caterpillar larvae feeding on elevated CO₂-grown leaves, while early instar gypsy moth larval NUE remained unchanged among the treatments. Later instar larvae of both insect species experienced larger reductions in foliage quality on elevated CO₂-grown leaves than earlier instars, as the carbohydrate:nitrogen ratio of leaves substantially increased. Despite this, neither insect species exhibited changes in growth or consumption rates between CO₂ treatments in the later instar. An increase in NUE was apparently responsible for offsetting reduced foliar nitrogen for the late instar larvae of both species.     

Effects of kaolin-based particle film application on boll weevil (Coleoptera: Curculionidae) injury to cotton

This study examined a non-insecticidal tactic for suppressing boll weevil, Anthonomus grandis grandis Boheman, damage to cotton, Gossypium hirsutum L. In cage assays, kaolin, a reflective white mineral, applied to excised cotton squares or to the cotton foliage, initially resulted in lower levels of boll weevil injury to squares than nontreated squares. Boll weevil oviposition and feeding on kaolin-treated squares and squares on kaolin-treated cotton plants increased when nontreated squares and cotton plants were in short supply. A laboratory assay and field trials suggested that boll weevils distinguished between cotton plots based on color differences caused by kaolin and this appeared to influence levels of damage to squares. Random sampling in small plots indicated that oviposition damage to squares in plots treated with kaolin was reduced (P < 0.05) compared with nontreated controls, except when rain washed the kaolin off the foliage. Lint yield differences were not detected between the small plots, but the kaolin-treated small plots yielded as much as 2.36 times more cotton lint than a large but unreplicated adjacent nontreated control plot, and up to 1.39 times more than another large but unreplicated adjacent plot sprayed twice with preemptive applications of azinphosmethyl when cotton squares were first developing (pinhead stage). Potentially important avenues for future research on boll weevil injury suppression using kaolin are discussed.     

Effects of a kaolin-based particle film on obliquebanded leafroller (Lepidoptera: Tortricidae)

Studies were conducted in 1997 to evaluate the effects of the kaolin-based particle film formulation M96-018 on adults, eggs, and larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris). Particle film treatments significantly reduced female longevity, mating success, and number of egg masses oviposited compared with moths on untreated apple leaves in sleeve-cage and screen-cage tests. No differences in mating success or oviposition were caused by the application rates and coverage density of M96-018 on foliage. Females avoided ovipositing on particle film-treated leaves in choice tests. Larval hatch was not affected by topical application or residual exposure to M96-018. Larval weight gain and pupal weight were significantly reduced and larval mortality increased in no-choice feeding tests with M96-018. In choice tests, larvae preferred to feed on untreated leaf surfaces. The negative effects on larval development and survivorship on M96-018-treated foliage did not differ across a fourfold difference in spray application rate. A significant reduction in the number of infested shoots was found in orchard trials when M96-018 was applied before bud break in late March compared with untreated trees. No reductions in larval densities were found compared with an untreated control following prebloom and postbloom applications.     

Particle films for suppression of the codling moth (Lepidoptera: Tortricidae) in apple and pear orchards

Studies were conducted in 1997 and 1998 to evaluate the effects of three particle film formulations consisting of kaolin and adjuvants on neonate larvae, ovipositing adult females, and eggs of the codling moth, Cydia pomonella (L.). Neonate larval walking speed, fruit discovery rate, and fruit penetration rate on apple host plants coated with particle films were significantly lower than on host plants without particle films in laboratory assays. Females oviposited less on host plants covered with a particle film residue than on untreated plants in laboratory choice and no-choice tests. Hatch rate of codling moth neonate larvae was unaffected by particle films sprayed on host plants either before or after oviposition. Fruit infestation rates were significantly reduced on particle film-treated trees compared with untreated trees for both first- and second-generation codling moth in field trials in both apple and pear orchards. Particle films appear to be a promising supplemental control approach for codling moth in orchards where moth density is high, and may represent a stand-alone method where moth densities are lower.     

Effects of kaolin on the composition of generalist predator assemblages and parasitism of Choristoneura rosaceana (Lep., Tortricidae) in apple orchards

Abstract:  In three apple orchards, we tested how the hydrophilic kaolin clay particle film Surround WP affected the diversity of generalist arthropod predator assemblages in orchard foliage and the parasitism of the pest species Choristoneura rosaceana (Harris) (obliquebanded leafroller) (Lep., Tortricidae). In two orchards, kaolin was applied to orchard foliage once a week for 4 weeks, between mid-June and mid-July in 2004 and 2005. In the third orchard kaolin was applied to foliage twice over 2 weeks in June 2004. We quantified the proportion of larvae C. rosaceana parasitized, larval populations, and the relative abundance and assemblage composition of generalist predators (spiders and insects) in the orchards. Kaolin altered the species composition of the generalist predator assemblages and reduced the relative abundances of certain generalist predators, most notably jumping and crab spiders (Salticidae and Philodromidae), assassin bugs (Reduviidae), ants (Formicidae) and coccinellids (Coccinellidae). In contrast, the relative abundances of web-spinning spiders (Araneidae, Dictynidae, Theridiidae) were not affected. Kaolin did not affect the proportion of parasitized C. rosaceana larvae, which ranged from 24% to 47% in control and kaolin treatments, or the relative proportions of parasitoid taxa. The kaolin formulation did not affect the abundance of C. rosaceana larvae, but in one orchard, kaolin did reduce the abundance of the combined numbers of C. rosaceana and another tortricid pest, Argyrotaenia velutiana . Although kaolin does not affect parasitism of C. rosaceana , it significantly changes the composition of generalist predator assemblages in orchard foliage.     

Predators ofLymantria dispar (Lep. lymantriidae) egg masses: Spatio-temporal variation of their impact during the 1988–89 pest generation in the mamora cork oak forest (Morocco)

In the Mamora cork oak forest (Morocco), oophagous predators of the gypsy mothLymantria dispar (L.) (Lepidoptera: Lymantriidae) are one of the main mortality factors influencing pest population dynamics. The predators destroy egg masses more by disrupting their cohesiveness than by predation. From 1987 to 1990, the impact of oophagous enemies significantly contributed to the collapse of a localized gypsy moth outbreak. Variation of egg mass dislocation intensity was greater between trees than among the different strata of a tree. The number of gypsy moth egg masses and egg predator attacks increased when oaks were large and unhealthy. Forest degradation probably explains why egg mass destruction rates were so high (60 to 90% of the eggs) in the infested forest. Oophagous predators find food and shelter under the dehiscent bark of unhealthy cork oaks.     

Effects of kaolin particle film on oviposition,larval mining,and infestation of cotton by pink bollworm (Lepidoptera: Gelechiidae)

We tested effects of kaolin particle film on oviposition, larval mining, and infestation of cotton by pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), in the laboratory, greenhouse, and field. In laboratory choice tests, females laid seven times more eggs on untreated bolls than on bolls treated with kaolin. When neonates were put on bolls in the laboratory, each boll with a treated and untreated half, larvae and mines were found 24 h later on the untreated half but not on the treated half. In oviposition choice tests with whole plants in the greenhouse, females laid four times more eggs on untreated plants than on treated plants and the number of eggs on bolls was five times higher for untreated plants than for treated plants. Kaolin treatments altered the distribution of eggs among plant parts, with untreated bolls receiving a higher percentage than treated bolls, whereas the opposite occurred for petioles. In field tests, treatment with kaolin alone reduced the proportion of bolls infested with pink bollworm, but a mixture of kaolin and the pyrethroid lambda-cyhalothrin was most effective. The results suggest that kaolin particle film may be useful against pink bollworm, particularly in conjunction with other control tactics.     

Intraspecific variation in aspen phytochemistry: effects on performance of gypsy moths and forest tent caterpillars

Individual quaking aspen trees vary greatly in foliar chemistry and susceptibility to defoliation by gypsy moths and forest tent caterpillars. To relate performance of these insects to differences in foliar chemistry, we reared larvac from egg hatch to pupation on leaves from different aspen trees and analyzed leaf samples for water, nitrogen, total nonstructural carbohydrates, phenolic glycosides, and condensed tannins. Larval performance varied markedly among trees. Pupal weights of both species were strongly and inversely related to phenolic glycoside concentrations. In addition, gypsy moth performance was positively related to condensed tannin concentrations, whereas forest tent caterpillar pupal weights were positively associated with leaf nitrogen concentrations. A subsequent study with larvae fed aspen leaves supplemented with the phenolic glycoside tremulacin confirmed that the compound reduces larval performance. Larvae exhibited increased stadium durations and decreased relative growth rates and food conversion efficiencies as dietary levels of tremulacin increased. Differences in performance were more pronounced for gypsy moths than for forest tent caterpillars. These results suggest that intraspecific variation in defensive chemistry may strongly mediate interactions between aspen, gypsy moths and forest tent caterpillars in the Great Lakes region, and may account for differential defoliation of aspen by these two insect species.     

Effects of kaolin particle film on Myzus persicae (Hemiptera: Aphididae) behaviour and performance

The emergence of resistance mechanisms to, and revocation of, many insecticides used in the control of the polyphagus aphid pest, Myzus persicae (Sulzer), has increased the pressure to develop novel approaches for the control of the pest in many crops. Kaolin-based particle films provide a physical barrier against insect pests and show considerable potential for controlling M. persicae. We conducted a series of laboratory experiments to investigate the mode of action of kaolin against aphids. The material appeared to have no direct effect on M. persicae; spraying adult aphids with aqueous kaolin suspension had no significant impact on their subsequent survival or reproduction on untreated plants. Similarly, when aphids were placed on kaolin-treated host-plants (Brassica oleracea), their performance (survival, growth rate and reproduction) was not significantly different from aphids on untreated plants. However, when M. persicae were given a choice between kaolin-treated and untreated (or water solvent-treated) leaf areas, both adults and nymphs exhibited a significant preference for non-kaolin-treated host-plant material. Rejection of kaolin-treated plant material occurred very rapidly (within 20 min) and this behavioural effect may be related to the efficacy of kaolin in controlling aphids under field conditions.     

Oviposition and feeding preference of Acrolepiopsis assectella Zell. (Lep., Acrolepiidae)

Abstract:  The leek moth, Acrolepiopsis assectella (Zell.), is a recently discovered exotic species in eastern Ontario and western Quebec. This Allium spp. (Asparagales, Alliaceae) specialist can cause up to 40% crop damage. A no-choice experiment was used to determine the relationship between oviposition behaviour and larval survival of the leek moth as the phylogenetic distance from the preferred host Allium ampeloprasum var. porrum L. increased. Results indicate that oviposition preference and larval survival of the leek moth declined as the phylogenetic distance from the preferred host increased. These results support the conclusion that the leek moth is a specialist feeder on closely related Allium spp. although the strength of this preference may decline as the motivation to oviposit increases. This may indicate that the leek moth is able to use closely related novel hosts as temporary refuges if the preferred host plant is unavailable.     

Effects of intentional gaps in spray coverage on the efficacy of gypsy moth mating disruption

Abstract:  The study was conducted during 2001 and 2002 in forested areas in Virginia, US to examine the effects of gaps in coverage of pheromone on gypsy moth, Lymantria dispar (L.) (Lep., Lymantriidae), mating disruption. Gypsy moth male moth catches in pheromone-baited traps were significantly reduced in plots treated with the gypsy moth sex pheromone, disparlure, at an overall application rate of 37.5 g of active ingredient (AI)/ha but with untreated gaps of 30 or 90 m between 30-m wide treated swaths. In one of the two plots with 90 m gaps, significantly more males were captured in traps in the untreated areas compared with the treated areas within the plot. However, in another plot, significant differences in trap catches between treated and untreated areas were not observed. No difference in male moth catches in the pheromone-baited traps was observed between treated and untreated areas within the plots treated with 30 m gaps. Female mating success did not differ significantly between treated and untreated areas within the one plot in which it was measured. These results suggest that it may be possible to lower costs associated with gypsy moth mating disruption applications by alternating treated and untreated swaths, which would reduce flight time and fuel costs, without a reduction in efficacy.     

Establishment and dominance of an introduced herbivore has limited impact on native host-parasitoid food webs

The gypsy moth is considered one of the most harmful invasive forest insects in North America. It has been suggested that gypsy moth may indirectly impact native caterpillar communities via shared parasitoids. However, the impact of gypsy moth on forest insect food webs in general remains unstudied. Here we assess such potential impacts by surveying forest insect food webs in Ontario, Canada. We systematically collected caterpillars using burlap bands at sites with and without histories of gypsy moth outbreak, and then reared these caterpillars until potential parasitoid emergence. This procedure allowed us to generate quantitative food webs describing caterpillar-parasitoid interactions. We estimated the degree of parasitoid sharing between gypsy moth and native caterpillars. We also statistically modeled the effect of gypsy moth outbreak history and current gypsy moth abundance on standard indices of quantitative food web structure and the diversity of parasitoid communities. Rates of gypsy moth parasitism were very low and gypsy moth shared very few parasitoids with native caterpillars, suggesting limited potential for indirect interactions. We did not detect any significant effects of gypsy moth on either food web structure or parasitoid diversity, and the small amount of parasitoid sharing strongly implies that this lack of significance is not merely due to low statistical power. Our study suggests that gypsy moth has limited impact on native host-parasitoid food webs, at least for species that use burlap bands. Our results emphasize that extrapolations of theoretical and experimental conclusions on the impacts of invasive species should be tested in natural settings.     

Intestinal modifications of oak leaf tannins by Lymantria dispar L. (Lep., Lymantriidae) and possible effect on larval development

The mode of action of polyphenols within an insect is not well understood and it would be useful to investigate the behaviour pattern of single phenolic compounds within the gut of an insect in this context. In the present study, the phenolic composition of the food of the gypsy moth, Lymantria dispar , was compared with that of its frass by using high-performance liquid chromatography. The main difference was a shift in the concentration of phenolics in the frass with short retention times to those with longer ones, which, additionally, resulted in the appearance of new phenolic compounds. These new phenolics were hydrolysable tannins because after a cleavage via hydrolysation the hydrolysate contained high amounts of gallic acid. The appearance of these new phenolics in the frass of the larvae influenced growth negatively, as there was a negative correlation (P < 0.05) between their concentrations and the growth percentages of the larvae.     

Kaolin-based particle film technology affects tomato physiology,yield and quality

Environmental stress can affect development and yield of tomato plants. This study was undertaken to investigate the underlying mechanism asserted by kaolin on tomato physiology by evaluating its effect on leaf, canopy and inner fruit temperatures, gas exchange at the leaf and canopy scales, above ground biomass, yield and fruit quality.The study was carried out under field conditions in Southern Italy. Treatments were plants treated with kaolin-based particle film (Surround^® WP) suspension and untreated plants (control).Kaolin application slightly increased leaf and canopy scale temperatures by 1.0 and 0.4 °C, respectively, transpiration rate decreased at both scales. On calm days (wind speed <0.5 m s^?1) with a prevalently clear sky at midday, inner fruit temperature (t_f) of kaolin-treated plants was 4.4 °C lower than the t_f of control plants, while in days with clear sky-windy, and cloudy-calm, the t_f did not differ.At leaf scale, net assimilation was reduced by 26% in kaolin-coated treatments. Stomatal conductance decreased by 53%, resulting in reductions of 34 and 15% in transpiration and internal CO₂ concentration, respectively. Gas exchange parameters measured at canopy scale were similarly affected. In kaolin-treated plants, assimilation and evapotranspiration rates were reduced by 17 and 20%, respectively, while dark respiration was not affected. Above ground dry biomass decreased by 6.4%.Marketable yield in kaolin-treated plants was 21% higher than those measured in control plants; this is possibly related to the 96 and 79% reduction in sunburned fruit and those damaged by insects, respectively, and to the 9% increase in mean fruit weight. Kaolin treatment increased lycopene fruit content by 16%, but did not affect total soluble solids content, fruit dry matter, juice pH, titratable acidity or tomato fruit firmness. The use of kaolin-based particle film technology would be an effective tool to alleviate heat stress and to reduce water stress in tomato production under arid and semi-arid conditions.     

Lygid bug damage as a pod access mechanism for Dasineura brassicae (Dipt., Cecidomyiidae) oviposition

Abstract: In a no-choice laboratory experiment, damage to Brassica napus pods created by Lygus feeding showed equivalent levels of Dasineura brassicae oviposition as both Ceutorhynchus assimilis damage and artificial injury (P > 0.05). No oviposition was recorded on undamaged controls (P < 0.01). Although Lygus damage provided equal pod access in the laboratory, lygid species are unlikely to be as efficacious a field vector as C. assimilis , primarily due to their less synchronous phenology.     

Behavioural response to an unsuitable host plant in the gypsy moth (Lymantria dispar L.)

To assess local differentiation in host preference, a two-choice test was performed on first-instar gypsy moth larvae originating from an oak and locust-tree forest. More than 40 generations feeding on locust-tree leaves, rich in alkaloids, led to non-efficient discrimination of host leaves in larvae from a locust-tree forest. Possible causes of observed population differences are discussed in the present paper.     

Particle film deters oviposition by Diaprepes abbreviatus (Coleoptera: Curculionidae)

A hydrophilic formulation of the inert silicate kaolin was tested in a screenhouse for its effect on the behavior of the root weevil Diaprepes abbreviatus (L.), a pest of citrus and ornamental plants in Florida and the Caribbean. Feeding by adults on treated foliage was reduced by 68-84% compared with adults fed untreated foliage. No insecticidal activity was detected after 14 d of exposure to kaolin-treated leaves. Oviposition was completely suppressed on treated foliage. Although females oviposited >19,000 eggs during two trials on untreated foliage, no egg masses were found on foliage treated with the kaolin formulation. These data indicate potential for kaolin as a barrier to oviposition in citrus groves and may prove to be an economically viable and environmentally sound component of an integrated approach for control of D. abbreviatus and related root weevils.     

A kaolin‐based particle film for suppression of the olive fruit fly Bactrocera oleae Gmelin (Dip., Tephritidae) in olive groves

The efficacy of a kaolin‐based particle film formulation M‐99‐099 to control olive fruit fly, Bactrocera oleae Gmelin, field infestations was investigated in north‐western Syria. The results showed that fruit infestation levels were significantly reduced on kaolin‐treated trees compared with untreated trees. Kaolin particle film successfully suppressed B. oleae populations and provided season‐long insect control (>14 weeks) whereas the insecticide dimethoate failed to protect olives for as long a period after the last spray. Consistent with previous findings, the M‐99‐099 kaolin particle film proved to be a promising alternative method to synthetic insecticides and could be used to control B. oleae in olive groves.     

Life table and biological studies of Harmonia axyridis Pallas (Col., Coccinellidae) reared on the grain moth eggs of Sitotroga cerealella Olivier (Lep., Gelechiidae)

The developmental period of immature stages, survival per cent, longevity, fecundity and life table parameters of Harmonia axyridis by feeding on fresh and frozen grain moth eggs (GME) of Sitotroga cerealella were studied under laboratory conditions. The effect of crowding adults on fecundity of females was also determined. The total developmental time from egg hatching to adult eclosion ranged from 18.89 ± 0.32 to 22.5 ± 0.21 days on fresh and frozen GME, respectively. Survival per cent from egg hatching to adult emergence differed significantly when the predator fed on the two diets of GME. Also, pupal and adult weights were affected by feeding on fresh and frozen GME. There were no significant differences in longevity of females, while there were significant variations in fecundity of females and longevity of males. The calculated values of T , DT , R_o , r_m , and e^rm were high by feeding on fresh GME. Morever, rates of survivorship ( Lx ), and maximum oviposition per female per day ( Mx ) were higher when the predator was reared on fresh than on frozen GME. Crowding conditions of predator adults affected the fecundity of females due to egg cannibalism by both males and females of the predator.     

Mechanical thinning to restore oak savanna promoted predator assemblages of gypsy moth pupae in Michigan

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