Cross‐resistance of chrysanthemum to western flower thrips,celery leafminer,and two‐spotted spider mite

Chrysanthemum [Chrysanthemum × morifolium Ramat. (Asteraceae)] is one of the economically most important greenhouse ornamentals worldwide. A major constraint in chrysanthemum production is adequate pest management, requiring the use of different tactics, such as improving host plant resistance, in the framework of an integrated pest management (IPM) approach. In this study, we investigated cross‐resistance of chrysanthemum to its three major pests: western flower thrips [Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)], celery leafminer [Liriomyza trifolii (Burgess) (Diptera: Agromyzidae)], and two‐spotted spider mite [Tetranychus urticae Koch (Acari: Tetranychidae)]. We quantified resistance to each pest by performing greenhouse bioassays with a broad range of chrysanthemum types from commercial germplasm provided by Dutch breeding companies. Considerable variation was detected among the chrysanthemum cultivars in thrips silver damage and growth damage, leafminer damage, measured as number of mines and pupae, and spider mite numbers and damage. We observed significant positive correlations between thrips damage (both silver and growth damage) vs. leafminer numbers (both mines and pupae), and between leafminer numbers (both mines and pupae) vs. spider mite numbers. Our results indicate an overlap in resistance to all three herbivores. The important implications of this result for chrysanthemum breeding are discussed.     

Laboratory rearing and biological parameters of the eulophid Pnigalio agraules,a parasitoid of Cameraria ohridella

Predators as well as parasitoids native to Europe accept the exotic horse chestnut leafminer, Cameraria ohridella Deschka and Dimi? 1986 (Lepidoptera: Gracillariidae), either as prey or as host. However, the influence of these antagonists on the populations of the pest insect is so far very low. Therefore, efforts to develop an integrated pest management system against C. ohridella should include methods which foster the natural enemy complex. In the present study we developed a laboratory rearing method and investigated several biological parameters of Pnigalio agraules (Walker 1839) (Hymenoptera: Eulophidae), a dominant species in the horse chestnut leafminer’s parasitoid complex in many European regions. This native parasitoid satisfies three basic requirements for successful use as a biocontrol agent with regard to C. ohridella. The parasitoid’s fecundity, longevity and the speed of juvenile development by far exceeds that of the leafminer, enabling the parasitoid population to increase faster than that of the host. Furthermore, our results show that the impact of this species on C. ohridella populations has been previously underestimated, because non‐reproductive killing (i.e. host‐feeding and host‐stinging) of the hosts, resulting in considerable larval mortality of the leafminer, has not been quantitatively assessed. However, naturally occurring parasitoid populations have negligible impact on C. ohridella populations. Further studies, including experimental releases of P. agraules, are necessary to understand the constraints limiting the parasitoid’s performance in the field and to assess the potential benefits of releases for the control of C. ohridella.     

Impact of natural enemies on coffee leafminer Leucoptera coffeella (Lepidoptera: Lyonetiidae) population dynamics in Chiapas, Mexico

Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previous studies suggested that its population dynamics were strongly affected by natural enemies, particularly of larvae, and physical environmental conditions. Our study documented through field surveys and life table analyses (i) the natural enemy complex associated with coffee leafminer and (ii) the impacts of natural enemies on the population dynamics of coffee leafminer, on coffee (Coffea arabica) at two elevations and two rainfall levels in the Soconusco region of Chiapas, Mexico. Twenty-two larval parasitoid species (including 14 morphospecies) were collected. Egg and pupal parasitoids were not recovered. Life table analyses showed that parasitism contributed 10% of real mortality, and parasitism rates were 8–10-fold higher at the low (<550 m) versus high (>950 m) elevation; parasitism rates were similar under low (<100 mm) and high (>400 mm) rainfall. Seventeen predator species (including five morphospecies) were collected, of which most were ants (Formicidae, 14 species) that contributed >58% of real mortality. Life table analyses showed that predation rates were higher at high versus low elevation and under high versus low rainfall. Independently of elevation and rainfall, egg predation (likely by ants) was the most important source of indispensable mortality (range = 0.13–0.30), except at low elevation and high rainfall where pupal predation (=0.14) was similarly important. Also, predation was the main source of coffee leafminer larval and pupal mortality during a 13-month period in a low elevation coffee farm and was highest during the rainy season (>400 mm rainfall/month), when coffee leafminer prevalence was highest. Overall, predation of eggs and pupae (the latter particularly at low elevation), mostly by ants, were the most important sources of coffee leafminer mortality. Because ants were the main source of coffee leafminer egg and pupal mortality, their importance and potential role in coffee pest management strategies were discussed.     

The Influence of Parasitoids (Hymenoptera,Eulophidae) on Survival of the Lime Leafminer <Emphasis Type="Italic">Phyllonorycter issikii</Emphasis> (Lepidoptera,Gracillariidae) in Udmurtia

The species structure of parasitoids (Hymenoptera, Eulophidae) of the invasive lime leafminer Phyllonorycter issikii (Kumata, 1963) (Lepidoptera, Gracillariidae) was reexamined ten years after the latest survey. The work was carried out in 2015 in three previously selected test plots within the city of Izhevsk. Extremely high survival rates (61.7 to 89%) of the leafminer were observed while the parasitoid complex had a negligible impact on its mortality (0.6 to 1.6%). A slight structural transformation of the parasitoid complex was noted, namely a decrease in the number of dominants and a change of the dominant species. In addition, the species structure of the parasitoids collected in 22 populated localities in Udmurtia was studied in 2016. Five new parasitoids of the lime leafminer were found: Pnigalio pectinicornis (Linnaeus, 1758), Sympiesis acalle Walker, 1848, Chrysocharis amanus Walker, 1839, Ch. pentheus Walker, 1839, and Ch. polyzo Walker, 1839. Two species of parasitoids of Ph. issikii were recognized as new to Udmurtia: Pnigalio agraules (Walker, 1839) and Pediobius saulius (Walker, 1839).     

A gene silencing of V‐ATPase subunit A interferes with survival and development of the tomato leafminer,Tuta absoluta

RNA interference (RNAi) technology is not only considered as a tool to analyze gene function, but it is also potentially considered as a strategy to develop novel biopesticide. In the current study, a double‐stranded RNA specific to v‐ATPase subunit A of the tomato leafminer, Tuta absoluta (Meyrick; Lepidoptera: Gelechiidae), was orally administered. A gradual decrease in the expression of the gene was observed from Day 1 to 3 and resulted in significant larval mortality. These results suggest that v‐ATPases A can be considered as a promising target gene by RNAi technology to be used in the management of the tomato leafminer.     

Parasitism of Cameraria ohridella (Lepidoptera, Gracillariidae) in natural and artificial horse-chestnut stands in the Balkans

1 The horse‐chestnut leafminer, Cameraria ohridella Deschka & Dimic, was discovered during a mass outbreak on planted horse‐chestnut trees, Aesculus hippocastanum, near Lake Ohrid in Macedonia. However, several peculiarities in the leafminer's biology and ecology, such as its inefficient control through natural enemies, indicate that it may be of exotic origin. 2 In this study, the parasitism of C. ohridella was examined in natural and artificial horse‐chestnut stands in South‐eastern Europe. The size and composition of the parasitoid complex of natural stands was comparable with that known from artificial stands. No specialist parasitoid species were detected in any of the samples. The only parasitoid species found exclusively in natural stands during this investigation were the braconid Colastes braconius and the eulophid Chrysocharis phryne. Both are known to be polyphagous on many leafminers in Europe and C. braconius has been often recorded from C. ohridella in artificial stands in previous studies. Parasitism levels varied within the same range (3.6–21.0%) throughout the entire region, in both types of habitats. 3 These results suggest that the parasitoid complex of C. ohridella in natural and planted horse‐chestnut stands in Europe is typically that of an exotic, recently introduced leafminer. Consequently, C. ohridella is probably not indigenous in the Balkans, but has been introduced to the area of its discovery from another continent.     

Distribution of the lime leafminer <Emphasis Type="Italic">Phyllonorycter issikii</Emphasis> (Lepidoptera,Gracillariidae) in natural stands

The spatial distribution of the lime leafminer Phyllonorycter issikii was studied in natural stands. The number of mines increased with shading of host-plant leaves. The maximum density of the miner was found in closed lime and spruce forests. The number of mines increased vertically from the tree top to its butt and horizontally, from the apex of branches to their base.     

Natural mortality factors of Leucoptera coffeella (Lepidoptera: Lyonetiidae) on Coffea arabica

The natural mortality of the coffee leafminer, Leucoptera coffeella (Guérin-Méneville) was investigated in three strata of coffee plant canopy for three seasons through construction and analysis of ecological life tables. Mortality of the leafminer was similar on all thirds of the canopy. Total mortality of immature stages was 95%, with 38.5, 43.8 and 12.7% occurring during egg, larval, and pupal stages. Rainfall killed 39.3% of eggs and larvae, and together with egg inviability (16.3%) and Vespidae (11.3%), were the highest mortality factors. Six wasp parasitoids caused 8% of larval mortality. Egg and larva were the critical stages. Variation in mortality was primarily associated with egg inviability, rainfall, and parasitism by Horismenus sp. (Hymenoptera: Eulophidae). Physiological disturbances during molting and metamorphosis also contributed for fluctuations in mortality of the leafminer. Tactics of integrated pest management to enhance natural mortality of the leafminer while conserving or augmenting the action of natural enemies are discussed.     

Indigenous parasitoids (Hym., Chalcidoidea) of Phyllocnistis citrella Stainton (Lep., Gracillariidae) in Jaguariúna, São Paulo State, Brazil: preliminary results

Abstract: The citrus leafminer, Phyllocnistis citrella Stainton, is native to Asia and was detected for the first time in Brazil in 1996. The objectives of this study were to conduct a survey of parasitoids attacking citrus leafminer in Jaguariúna, one of the citrus production regions of São Paulo State, Brazil, and to determine whether indigenous species were providing effective control of this pest species. The collections of new leaves were made weekly at citrus groves in Jaguariúna from October 1996 to October 1997. Of the six indigenous parasitoids which were found, Galeopsomyia fausta LaSalle was the most abundant parasitoid of P. citrella in this region, accounting for more than 90% of the specimens collected. Thus, this species is a serious candidate for biological control of the citrus leafminer in this region of Brazil. Other species collected were Horismenus sp., Cirrospilus 'sp. C', Elasmus sp., Eupelmus sp. and Conura (Ceratosmicra) sp. The mean percentage of parasitism was 39.28% (6.19−86.21%) in unsprayed orchards and 21.38% (1.33−56.63%) in orchards that were occasionally treated with fungicides, acaricides and insecticides Temik and Dipterex.     

Biological invasion of the lime leafminer <Emphasis Type="Italic">Lithocolletis issikii</Emphasis> Kumata (Lepidoptera,Gracillariidae): Interaction of the moth with the host plant

Interrelations between the lime leafminer, Lithocolletis issikii Kumata (Lepidoptera, Gracillariidae) and the small-leaved linden Tilia cordata Mill. were studied. A significant positive correlation between the number of mines per leaf and the surface areas of individual mines was found. The interaction in the linden-lime leafminer system was found to be active: an increase in the pest density is followed by a significant increase in an individual mine surface area.     

Effects of cyromazine and abamectin on the leafminer, Liriomyza huidobrensis and its parasitoid, Diglyphus isaea in celery

Field trials were conducted for 2 yr on celery (Apium graveolens L.) to determine the effects of two translaminar insecticides (abamectin and cyromazine) on the agromyzid leafminer, Liriomyza huidobrensis (Blanchard), and the eulophid parasitoid, Diglyphus isaea Walker. Abamectin and cyromazine were applied once early in the growing season by spray or drip application. Yellow sticky traps and leaf samples were used to monitor population levels; a gas chromatograph-mass spectrometer was used to monitor cyromazine residues within the celery plants during 1 yr. Spray applications of abamectin and cyromazine significantly reduced larval leafminers and D. isaea. Contrary to grower practices, application of cyromazine by drip irrigation systems had minor effects on larval leafminer and D. isaea as compared to spray application. Cyromazine residues in the plants treated by spray application declined sharply after 1 wk, and no residues were detected 2 wk after application; less than 0.05 ppm cyromazine residues were detected in plants treated by drip application. Implications of these results on management practices are discussed.     

Cameraria ohridella: 10 years of sex pheromone and kairomone research

This review traces the identification and use of sex pheromone of the horse chestnut leafminer Cameraria ohridella Deschka et Dimi? (Lepidoptera, Gracillariidae, Lithocolletinae) to monitor population density and discuss its potential for direct control. Host volatiles endogenously emitted from Aesculus hippocastanum L. leaves are described in terms of their ability to control conspecific females.     

A new microbial consortia containing entomopathogenic fungus,Beauveria bassiana and plant growth promoting rhizobacteria,Pseudomonas fluorescens for simultaneous management of leafminers and collar rot disease in groundnut

The virulence of 20 isolates of Beauveria bassiana (Balsamo) Vuillemin to larvae of the leafminer, Aproaerema modicella, was tested in the laboratory. Leafminer larvae were sprayed with a standard concentration of 1×10⁸ condia/mL of each B. bassiana isolate. All the B. bassiana isolates tested were pathogenic to A. modicella and the mortality varied between 16.7 and 68.9%. Beauveria bassiana isolate B2 was found to be the most virulent followed by isolate B4 which resulted in 59% mortality. Beauveria isolate B2 was selected for dose–response mortality studies with four different doses (1×10², 1×10⁴, 1×10⁶ and 1×10⁸ conidia/mL). Among the various doses tested, 1×10⁸ conidia/mL produced the highest mortality (70.7%). In addition, morphogenesis of the insect pest in all stages, larval, pupal and adult was greatly affected due to fungal infection. Further, B. bassiana isolate B2 and two Pseudomonas fluorescens strains, TDK1 and Pf1 were tested alone and in combination for suppression of groundnut leafminer and collar rot disease and promotion of plant growth and yield both under glasshouse and field conditions. The mixture of B. bassiana and P. fluorescens strains significantly reduced the leafminer and collar rot disease incidences when applied as talc-based formulation through seed, soil and foliar application under glasshouse and field conditions.     

Parasitism of different larval stages of Cameraria ohridella

About 20 species of parasitic Hymenoptera havebeen reported from the horse chestnutleafminer, Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae). Generally,parasitism is low compared to other closelyrelated leafminers and the parasitism levelvaries considerably. Among other reasons,parasitism rates depend on the developmentalstage of the moth and therefore vary with thesampling date. In the current study,investigations on the parasitism of the moth'sfirst generation were carried out in order todetermine which preimaginal stages areparasitized by the most abundant parasiticwasps. Minotetrastichus frontalis (Nees),Pnigalio agraules (Walker) and Chrysocharis nephereus (Walker) (allHymenoptera: Eulophidae) developed as larval orpupal parasitoids and preferred later larvalinstars of the moth. Egg parasitism did notoccur. Overall, the last two of the six larvalinstars (the spinning instars) of the leafminersuffered the heaviest attack. In concordancewith the fairly low parasitism rates, theeffect of the four most abundant chalcidoids onthe leafminer population was negligible, havingno significant influence on the mortality ofC. ohridella. Although the speciescomposition of the parasitoid complex of C. ohridella shows similarities with thesituation found in other closely relatedleafmining moths, it is unlikely that thenaturally occurring chalcidoids will be able toprevent the horse chestnut leafminer fromdeveloping epidemic population densities in thenear future.     

Occurrence and phenology of parasitic Chalcidoidea on the horse chestnut leafminer,Cameraria ohridella Deschka & Dimic (Lep., Gracillariidae)

Abstract: The parasitoid spectrum of the horse chestnut leafminer, Cameraria ohridella, was examined for its adaptation to a newly introduced host. A total of 15 parasitic species belonging to the suprafamilies Ichneumonoidea and Chalcidoidea was reared, all of them are polyphagous and common on other leafminers in Europe. The abundance of the moth and its natural enemies were studied during one entire vegetation period. The phenology of some of its major parasitic species was investigated and compared with the occurrence of the leafminer with special regard to its possible use in biological pest control.     

A 3 year field survey of the natural enemies of the horse-chestnut leaf miner <Emphasis Type="Italic">Cameraria ohridella</Emphasis> in Lombardy,Italy

A survey to inventory the natural enemies of the horse-chestnut leafmining moth, Cameraria ohridella Deschka and Dimic (Lepidoptera, Gracillariidae) and to evaluate their relative abundance, was conducted from 2001 through 2003 in Lombardy, northern Italy. Two predators and 10 parasitoids were found during the 3-year survey. An increasing number of parasitoid species associated with the leafminer was detected (4 species in 2001, 5 in the 2002 and 10 in 2003). Eulophidae (Hymenoptera: Chalcidoidea) were most represented: Minotetrastichus frontalis Nees, Closterocerus trifasciatus Westwood, Pnigalio pectinicornis L., Pnigalio agraules Walker, Pediobius saulius Walker, Chrysocharis pentheus Walker, Cirrospilus talitzkii Bouek, Sympiesis sericeicornis Nees, Baryscapus nigroviolaceus (Nees). Only one Ichneumonidae (Hymenoptera: Ichneumonoidea) was found during 2003: Itoplectis alternans (Grav.).     

A tritrophic analysis of host preference and performance in a polyphagous leafminer

The optimal oviposition theory predicts that oviposition preferences of phytophagous insects should correlate with host suitability for their offspring. As plant host suitability depends not only on its quality as food, but also on its provision of enemy‐free space, we examined the relationship between adult host preference and offspring performance for the leafminer Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) on various host plants, considering also the interaction with natural enemies. Preference and offspring performance were assessed through observational field data and laboratory experiments in central Argentina. Field data suggested a positive host preference – performance linkage, as the leafminer attained larger body size on the crops where it was more abundant. Laboratory trials supported these results: Vicia faba L. (Fabaceae) was the preferred host in the laboratory as well as in the field, performance of L. huidobrensis being also best on this host, with highest survival rates and shortest development time. The actively feeding larval stage showed the largest plant‐related effects. Higher overall parasitism rates were found on plants from which smaller leafminers were reared, reinforcing the preference–performance linkage. On the other hand, the main parasitoid Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) reached larger body size, and caused higher mortality rates on crops where the leafminer was larger. Changes in abundance of particular parasitoid species could thus modify overall parasitism trends.     

Dynamic economic thresholds for the management of vegetable leafminer on glasshouse cucumber estimated by simulated defoliation

Defoliation by the vegetable leafminer, Liriomyza sativae Blanchard (Diptera: Agromyzidae), was simulated by removing known amounts of leaf area with a hole punch in a glasshouse experiment that evaluated 21 combinations of defoliation intensity, timing and duration on cucumber yields. Defoliation was quantified in cm²-days (leaf area removed x no. days), and linear regression was used to correlate yield losses to simulated damage. The probability of erroneous decisions associated with different intensities of sequential sampling was explored. Spatial heterogeneity in leafminer infestation and the cumulative impact of defoliation over time were both considered, and the economic costs associated with wrong decisions were also assessed. Significant yield loss was observed beyond 10,000 cm²-days of defoliation, whereas lower defoliation levels were tolerated by plants. The economic injury level (EIL) rose at an increasing rate as the onset of defoliation moved later in the season. An algorithm was used to estimate monthly EILs that farmers can use to guide leafminer management decisions in cucumber and minimize their economic risk.