Host suitability of the Mediterranean flour moth for rearing <Emphasis Type="Italic">Meteorus pulchricornis</Emphasis> (Hymenoptera: Braconidae), a polyphagous endoparasitoid of pest lepidopteran larvae

We investigated the host suitability of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) for a polyphagous koinobiont endoparasitoid Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae), a common natural enemy of various pest lepidopteran larvae. The estimated probability of adult wasp emergence was 80% or higher when eggs were laid in nearly fully grown larvae of E. kuehniella (fresh weight, >?20.0 mg). The body size of emerged adult wasps increased with the initial weight of the host larvae at oviposition. The fresh weight of adult wasps reared on E. kuehniella was approximately 60% of that when reared on a natural host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), and the lifetime fecundity of wasps reared on E. kuehniella was approximately half of that when reared on S. litura. Ephestia kuehniella was shown to be a positive host candidate for the mass rearing of M. pulchricornis, but further investigation is needed to increase the body size of wasps for more practical use of this species as a biocontrol agent.     

Innate Olfactory Responses of <Emphasis Type="Italic">Asobara japonica</Emphasis> Toward Fruits Infested by the Invasive Spotted Wing Drosophila

Insect parasitoids are often manipulated to improve biological control programs for various arthropod pests. Volatile compounds can be a relevant cue used by most parasitoid hymenoptera for host or host microhabitat location. Here, we studied olfactory responses of the braconid Asobara japonica Belokobylskij, an Asiatic endoparasitoid of the invasive pest Drosophila suzukii (Matsumura), toward its host and host substrates. Adult A. japonica displayed an innate attraction to undescribed volatile cues from infested host fruits irrespectively of the juvenile rearing experience, i.e. they respond to a novel cue subsequently used for microhabitat selection. These data suggest that A. japonica parasitoids mass-reared on artificial diet and factitious host (D. melanogaster) can successfully locate their hosts. Naïve female parasitoids did not show a preference towards any of the tested host media. However, the enforced adult experience with the rearing host medium modified the olfactory preference patterns toward non-natal host fruits. These findings provide evidence of associative learning during the adult stage of A. japonica, and demonstrate its plasticity in exploiting the volatiles from various fruits infested by D. suzukii.     

Rate of consumption,biological parameters,and population growth capacity of <Emphasis Type="Italic">Orius laevigatus</Emphasis> fed on <Emphasis Type="Italic">Spodoptera exigua</Emphasis>

Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) is already successfully used to control Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in protected crops. In the present work, the predatory capacity of O. laevigatus on the eggs and larvae of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) as well as the population growth capacity of O. laevigatus fed on eggs of the noctuid were determined. Fourth and 5th instar nymphs had a greater consumption of eggs than younger ones. Females consumed more eggs than males. Only 5th instar nymphs and adults preyed on the neonatal larvae of S. exigua. The intrinsic rate of natural increase did not differ between O. laevigatus fed with S. exigua eggs and those offered eggs of the substitute host Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae). Thus, O. laevigatus is a good candidate for the biological control of S. exigua, a cosmopolitan pest of many crops.     

Optimization of Methodology for Rearing <Emphasis Type="Italic">Spodoptera albula</Emphasis> on Artificial Diet

Advances in techniques for rearing insects on artificial diets are fundamental to solving issues of basic and applied entomology. In this study, we evaluated the development of Spodoptera albula (Walker) (Lepidoptera: Noctuidae) on three artificial diets used for other species of Lepidoptera, at three larval densities, and two densities of adult couples housed in oviposition cages of two sizes, with the aim of optimizing methodology for rearing S. albula in the laboratory. Biological parameters were recorded from S. albula, and a fitness index was calculated based on the larval survival and duration and weight of pupae. The total and daily oviposition was recorded using 5 or 10 adult couples of S. albula housed in two cage sizes. Concentrations of total nitrogen and protein in the tested diets were determined. Development of S. albula was completed in all artificial diets; however, the diet used for rearing Anticarsia gemmatalis (Hübner) larvae was the most suitable for S. albula, yielding intermediate development time and higher survival relative to the other diets. Individualization of larvae favored S. albula development by producing overall greater weights of larvae and pupae, higher survival rates, and longer adult longevity. Cage size and number of couples per cage did not influence S. albula fecundity in the experiment conditions. Spodoptera albula can be satisfactorily reared on the artificial diet used for A. gemmatalis, using one larva per tube, and either density of adults at any cage size. Additional amendments are needed in the rearing methodology to achieve optimal conditions for larval development to adulthood.     

Trabala Vishnou Gigantina Yang (Lepidoptera: Lasiocampidae) Larval Fitness on six Sympatric Plant Species in Sea-Buckthorn Forest

Trabala vishnou gigantina Yang (Lepidoptera: Lasiocampidae) is a major pest that damages the sea-buckthorn, Hippophae rhamnoides. We observed and compared the feeding preferences of T. vishnou gigantina larvae on six sympatric plant species in a two-choice test. We also compared T. vishnou gigantina fitness, as measured by the following variables: larvae weight, developmental period, pupae versus adult weight, longevity, and fecundity rates. Between host and non-host plants, larvae showed a strong preference for their natural host (sea-buckthorn), followed by apricot, poplar, and willow. Caragana and locust were the least preferred plants when the natural host plant was not present. Larvae reared on sea-buckthorn possessed greater pre-pupal weight, had lower mortality, and developed more quickly into heavier pupae than either poplar-raised or willow-raised larvae. Fecundity was highest on sea-buckthorn, second highest on apricot, and lowest on poplar. Longevity (of both females and males) was not significantly different across plant species. These results clearly demonstrate that T. vishnou gigantina larvae are able to distinguish between host versus non-host plants, and that their preference translates to increased fitness. Possible, non-mutually exclusive explanations for observed preference and fitness differences include variation in required nutritional content across plant species or the presence of plant traits (morphological features or chemical metabolites) that negatively affect larval development. While the exact mechanisms are unknown, these data may be useful for the development of appropriate counter-measures to the damage caused by T. vishnou gigantina on sea-buckthorn.     

Putative Host Volatiles Used by <Emphasis Type="Italic">Habrobracon hebetor</Emphasis> (Hymenoptera: Braconidae) to Locate Larvae of <Emphasis Type="Italic">Plodia interpunctella</Emphasis> (Lepidoptera: Pyralidae)

Indianmeal moth, Plodia interpunctella (Hubner) (Lepidoptera: Pyralidae), is a post-harvest pest of grains, milled and processed food, processing plants, warehouses and bakeries. The parasitoid, Habrobracon hebetor (Say) is among the most important natural enemies of Pyralidae infesting stored grains and grain products. Many parasitoids use semiochemicals originating from their hosts, or host’s habitat as cues to locate hosts, hosts’ food or habitat. The authors used Y-tube and four-way olfactometers to assay responses to stimuli with the moth host and thereby understand the role of host-associated semiochemicals in host location by H. hebetor. Responses of mated parasitoid females were assayed to the following stimuli: P. interpunctella sex pheromone, female adults, larvae, or hexane extracts of residue of the rearing medium. Generally, host-related odor sources generated stimuli that elicited better responses than those to blank controls. Previous exposure to odor sources from the host shortened latency periods and response times compared to naïve females. Odors emanating from live moth larvae elicited the strongest responses. When responses from the four odor sources were compared in a four-way olfactometer, it was confirmed that volatiles from larval moths elicited the strongest attraction to the parasitoid. The involvement of host-specific chemical cues in both long and short range host location by female parasitoid is discussed.     

The <Emphasis Type="Italic">Cotesia sesamiae</Emphasis> story: insight into host-range evolution in a Hymenoptera parasitoid and implication for its use in biological control programs

This review covers nearly 20 years of studies on the ecology, physiology and genetics of the Hymenoptera Cotesia sesamiae, an African parasitoid of Lepidoptera that reduces populations of common maize borers in East and South Africa. The first part of the review presents studies based on sampling of C. sesamiae from maize crops in Kenya. From this agrosystem including one host plant and three main host borer species, studies revealed two genetically differentiated populations of C. sesamiae species adapted to their local host community, and showed that their differentiation involved the joint evolution of virulence genes and sensory mechanisms of host acceptance, reinforced by reproductive incompatibility due to Wolbachia infection status and natural inbreeding. In the second part, we consider the larger ecosystem of wild Poales plant species hosting many Lepidoptera stem borer species that are potential hosts for C. sesamiae. The hypothesis of other host-adapted C. sesamiae populations was investigated based on a large sampling of stem borer larvae on various Poales across sub-Saharan Africa. The sampling provided information on the respective contribution of local hosts, biogeography and Wolbachia in the genetic structure of C. sesamiae populations. Molecular evolution analyses highlighted that several bracovirus genes were under positive selection, some of them being under different selection pressure in C. sesamiae populations adapted to different hosts. This suggests that C. sesamiae host races result from co-evolution acting at the local scale on different bracovirus genes. The third part considers the mechanisms driving specialization. C. sesamiae host races are more or less host-specialized. This character is crucial for efficient and environmentally-safe use of natural enemies for biological control of pests. One method to get an insight in the evolutionary stability of host-parasite associations is to characterize the phylogenetic relationships between the so-called host-races. Based on the construction of a phylogeny of C. sesamiae samples from various host- and plant species, we revealed three main lineages. Mechanisms of differentiation are discussed with regard to the geography and ecology of the samples. One of the lineage presented all the hallmarks of a distinct species, which has been morphologically described and is now studied in the perspective of being used as biological control agent against Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a major maize pest in West Africa and Mediterranean countries (see Benoist et al. 2017). The fourth part reviews past and present use of C. sesamiae in biological control, and points out the interest of such molecular ecology studies to reconcile biodiversity and food security stakes in future biological control.     

Aseptic rearing procedure for the stinkbug <Emphasis Type="Italic">Plautia stali</Emphasis> (Hemiptera: Pentatomidae) by sterilizing food-derived bacterial contaminants

The stinkbug Plautia stali Scott is a notorious agricultural pest whose posterior midgut hosts specific bacteria essential for its growth and survival, highlighted as an experimental model for symbiosis studies. Some symbiotic bacteria of P. stali are cultivable, found free-living in and acquired from the environment, and, furthermore, some free-living environmental bacteria are potentially capable of establishing symbiotic association with P. stali. In this context, it is expected that such environmental bacteria may occasionally contaminate and infect the experimental insects maintained in the laboratory, which could potentially affect the functional analyses of the symbiosis. Here we report that such contamination events do occur under a laboratory rearing conditions for P. stali. When symbiont-deprived newborn nymphs from surface-sterilized eggs were reared in sterilized plastic containers with autoclaved water, most of them died as nymphs presumably as a result of aposymbiosis, but only a small fraction could attain adulthood and the adult insects were all infected with γ-proteobacteria allied to Pantoea and Enterobacter. A variety of bacteria, mainly Bacillus and also Pantoea and Enterobacter, were detected from peanuts and soybeans provided as food for P. stali. Autoclaving of peanuts and soybeans eradicated these bacteria but negatively affected the host survival, whereas ethanol sterilization of peanuts and soybeans removed Pantoea and Enterobacter, but not Bacillus, without negative effects on the host survival. On the basis of these results, we established a practical procedure for aseptic rearing of P. stali, which will enable reliable and strict analyses of host–symbiont interactions in the model symbiotic system.     

Phototactic Behavior of <Emphasis Type="Italic">Scleroderma guani</Emphasis> (Hymenoptera: Bethylidae) - Parasitoid of <Emphasis Type="Italic">Pissodes punctatus</Emphasis> (Coleoptera: Curculionidae)

Although light trap can be used to control pest populations, they can also kill the natural enemies of pests. Scleroderma guani (Hymenoptera: Bethylidae) is a parasitoid of a bark-weevil Pissodes punctatus (Coleoptera: Curculionidae). To understand the phototactic behavior of S. guani, we investigated its diurnal and nocturnal behavior, then examined its phototactic response to nine monochromatic lights and to five intensities of the two most attractive lights. Our results showed that S. guani is most active during the day, while remain still in a dark room or at night. S. guani showed a positive response both to a broad spectrum of monochromatic light and total light (natural light), which implies a broad sensitivity to the light spectrum. S. guani was most sensitive to blue (450 nm) and green (549 nm) lights, suggesting its visual system composed of blue and green receptors. S. guani was least sensitive to ultraviolet (340 nm) light, which may be caused by long-term mass rearing and propagating under artificial conditions. Furthermore, low intensities elicited a positive phototactic response, while high intensities showed a decreased trend under both blue and green lights. Thus, S. guani is a phototactic insect which shows preferences for light in both color and intensity. This study suggests that light trap can only be utilized to control the adult P. punctatus during and after its peak emergence, due to the overlap in the spectral sensitivity of both pest and parasitoid adults.     

An Experimental Test of Trade-Offs Associated with the Adaptation to Alternate Host Plants in the Introduced Herbivorous Beetle, <Emphasis Type="Italic">Ophraella communa</Emphasis>

The adaptation to alternate host plants of introduced herbivorous insects can be vital to agriculture due to the emergence of crop pests. Historically, it is assumed that there are trade-offs associated with the adaptation to new host plants; a generalist genotype that adapts to an alternate host is expected to have a relatively lower fitness on the ancestral host than a specialist genotype (physiological cost) or a relatively lower host-searching ability for the ancestral host plant (behavioral cost). In this study, we tested the costs of adaptation to a new host plant in the introduced herbivorous insect, Ophraella communa LeSage (Coleoptera: Chrysomelidae). In its native range (United States), O. communa feeds mostly on Ambrosia artemisiifolia L. (Asterales: Asteraceae) and cannot utilize the related species, Ambrosia trifida L. (Asterales: Asteraceae), as a host plant. On the other hand, the introduced O. communa population in Japan utilizes A. trifida extensively, and is adapting to it, both physiologically and behaviorally. We compared larval performance on the ancestral and alternate plants and adult host-searching ability between the native and introduced beetle populations. The introduced O. communa showed higher larval survival and adult feeding preference for the alternate host plant A. trifida than did the native O. communa, indicating that the introduced O. communa has rapidly adapted to the alternate host plant. However, there are no differences in either larval performance on the ancestral host A. artemisiifolia or host-searching accuracy between the native and introduced O. communa.     

Effects of intraspecific hybridization on the fitness of the egg parasitoid <Emphasis Type="Italic">Trichogramma galloi</Emphasis>

Successive rearing in laboratory conditions can result in the loss of genetic diversity, inbreeding depression and adaptation to the captive environment, affecting the quality of the insects reared and compromising their field performance. Introduction of genetic variation by admixing different populations may increase the fitness of populations, minimizing the negative effects of rearing many generations in artificial conditions. We experimentally investigated the role of intraspecific hybridization in enhancing the fitness of the egg parasitoid Trichogramma galloi Zucchi, 1988 (Hymenoptera: Trichogrammatidae), by reciprocally crossing three populations. Our results showed that the mating type did not affect the number of crosses that produced viable daughters. Homotypic crosses produced 94% viable daughters, while heterotypic crosses produced 92%. There were neither mating incompatibilities nor reproductive barriers between these populations. However, we observed a low fitness value for females from one of the populations studied. The fitness of hybrids was either unchanged or improved (in one case) when compared to the parental populations. We discuss the implications of our results and suggest future research directions.     

Host plants influence female oviposition and larval performance in West Indian sweet potato weevils <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae)

Euscepes postfasciatus (Fairmaire) is an invasive pest of the sweet potato (Ipomoea batatas) and is also parasitic to other wild host plants of the Ipomoea genus. The population density of E. postfasciatus is sometimes greater in Ipomoea pes-caprae L. than in Ipomoea indica (Burm. f.). We investigated the desirability of I. pes-caprae as a host plant for E. postfasciatus in terms of reproductive and developmental potential. Females laid fewer eggs on I. pes-caprae, and the eclosion of their larvae was delayed compared with on I. indica. Furthermore, the larval growth rate was slower on I. pes-caprae than on I. indica. These results suggest that I. pes-caprae is not always the preferred host for egg laying and growth rate in the early developmental stages. However, the larval survival rate after the initial period of development was markedly better on I. pes-caprae than on I. indica. The present simulation study demonstrated that the population density of E. postfasciatus on I. pes-caprae overwhelmed that on I. indica over generations. Comparing the two wild host plant species, I. pes-caprae outweighs I. indica with respect to total population growth, but reproduction on I. indica may be advantageous for the colonization of the new habitat.     

Does <Emphasis Type="Italic">Wolbachia</Emphasis> Infection Change the Overwintering Ability of <Emphasis Type="Italic">Trichogramma brassicae</Emphasis> (Hymenoptera: Trichogrammatidae)?

The overwintering ability of a biological control agent helps predict potential survival and establishment in natural conditions. Here, we compared the overwintering ability in sexual and asexual Trichogramma brassicae Bezdenko, a key natural enemy of Lepidopteran pests in Iran over two consecutive winters in central Alborz Mountains. Our aim was to investigate the effect of Wolbachia infection on the overwintering rate of T. brassicae after emergence in the subsequent year. We also wanted to know whether there is any difference in the overwintering capacity of T. brassicae populations either in terms of exposure date or emergence date. Parasitized host eggs were exposed under outdoor conditions between 8 October and 27 November 2013 and between 8 October and 11 December 2014. Samples were checked weekly until adult emergence of overwintered individuals in the following spring, and proportion of adult emergence was recorded on each exposure date. Our results demonstrated that both populations were able to overwinter in natural conditions of central Alborz Mountains; however, sexual T. brassicae was more successful in overwintering than asexual one. No differences were observed in the emergence date and maximum emergence rate between two populations. Our study clearly identified a potential negative impact of Wolbachia on fitness of T. brassicae by a lower rate of emergence.     

Fungi isolated from insects in strawberry crops act as potential biological control agents of <Emphasis Type="Italic">Duponchelia fovealis</Emphasis> (Lepidoptera: Crambidae)

Entomopathogenic fungi were collected from insects, belonging to orders Lepidoptera, Coleoptera, Hemiptera, Hymenoptera, and Diptera, with signs of infection. Single-spore colonies were identified based on morphological traits and ribosomal ITS sequences. The most commonly found fungi were Fusarium oxysporum Schlechtendal and Beauveria bassiana (Balsamo-Crivelli) Vuillemin. Isolation of Trichoderma atroviride Bisset, Aspergillus flavipes (Bainier and Sartory) Thom and Church, Aspergillus iizukae Sugiyama, Penicillium mallochii Rivera, Urb and Seifert, Penicillium adametzioides S. Abe ex G. Smith, and Mucor nidicola Madden, Stchigel, Guarro and Starks associated to insects is reported for the first time. Tests with B. bassiana isolates against Duponchelia fovealis Zeller (Lepidoptera: Crambidae), showed high larval mortality in vitro and in greenhouse, demonstrating its potential as biological control agent. Understanding the fungal microbiota from insects can provide promising isolates for use in integrated pest management programs. This is the first report characterizing the mycobiota in insects collected in strawberry crops, and evaluating the pathogenicity of B. bassiana against D. fovealis, a pest that causes severe losses to farmers.     

Rearing <Emphasis Type="Italic">Chrysoperla externa</Emphasis> Larvae on Artificial Diets

We tested three artificial diets for rearing larvae of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae), aiming at reducing the production costs of this predator. Two of the diets come from studies with other species of lacewings, and the third is a modification described in this paper. All diets were based on animal protein and were supplied to 2nd and 3rd instar larvae, whereas 1st instar larvae received eggs of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae). We evaluated the preimaginal duration and survival, adult size, longevity and fecundity, egg hatchability, and predatory capacity of larvae produced. The performance of the diets was followed for seven generations. The diet we describe showed to be the best among the artificial diets tested. Our results show that C. externa can be successfully reared on artificial diets during second and third instars, reducing in 90% the dependency on eggs of A. kuehniella.     

Dynamics of host plant selection and host-switching by silver-spotted skipper caterpillars

Investigations of host plant selection in herbivorous arthropods have emphasized the importance of oviposition site selection by adults; however, a more complete picture of this process requires additional consideration of the factors influencing host plant choice during the immature feeding stages. We conducted a series of larval choice experiments to examine both the innate and induced preferences of larvae of the Silver-spotted skipper (Epargyreus clarus L.) on three commonly used hosts (Wisteria, Robinia, and Pueraria). Late instar E. clarus larvae reared on each of the three host plants displayed an overall pattern of innate preferences that correlated well with larval performance measures and reflected differences in foliar nutrient concentrations. Larval preferences were also influenced by rearing host species, indicating a role for feeding-induced preferences. When larvae reared on low-quality Wisteria for the first four instars were switched to higher quality Pueraria for the final instar, they developed more quickly and attained significantly higher pupal mass than larvae maintained on Wisteria throughout development. Similarly, larvae switched from Pueraria to Wisteria for the final instar suffered increased development time and produced significantly smaller pupae than those maintained on Pueraria throughout. Thus host-switching, particularly during the more mobile final instars, appears to offer larvae an opportunity to recoup fitness losses associated with early development on a low-quality host. For an equal amount of consumption, larvae feeding on Pueraria gained 50% more mass than those feeding on Wisteria, reflecting measured differences in foliar nitrogen concentration; despite these overall differences in quality, larval growth efficiency was similar among hosts. Especially in the age of common exotic plant introductions, a full understanding of the behavioral component of host selection by herbivorous insects requires appreciation of the dynamic role that immatures can play in host selection and use.     

Effect of entomopathogenic nematodes on different developmental stages of <Emphasis Type="Italic">Drosophila suzukii</Emphasis> in and outside fruits

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a harmful invasive fruit pest, which is currently spreading in Europe. Since its arrival in 2008, the spotted wing drosophila has caused major losses in several soft-skinned fruit crops. This critical situation urgently requires efficient practices of residue-free pest control. In the present laboratory study, entomopathogenic nematodes (EPNs) were investigated for their ability to infect larvae and pupae of D. suzukii within directly sprayed fruit, fruit placed on soil, and soil. Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), and Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae) were more efficient at infecting soil-pupating host larvae than Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) at application rates ranging from 25 to 400 EPN cm^?2. Applied as a soil drench, S. feltiae and S. carpocapsae were able to infect D. suzukii larvae in the soil as well as hidden inside fruit. Direct application of EPNs on the fruit was less successful, although emergence of flies was significantly reduced.     

Selection of an Artificial Diet for Laboratory Rearing of <Emphasis Type="Italic">Opogona sacchari</Emphasis> (Lepidoptera: Tineidae) (Bojer, 1856)

The banana moth Opogona sacchari (Bojer) (Lepidoptera: Tineidae) is a polyphagous pest that can cause serious damage, in particular to banana crops in southern Brazil. The insect is a quarantine pest in several countries, including Argentina, the main consumer market for bananas from southern Brazil. Little information is available about the biology and ecology of this moth, such as a suitable diet for laboratory rearing. In order to provide support for integrated pest management of the pest, this study furnished data for selecting two diets suitable for continuous laboratory rearing of O. sacchari, one based on dried beans, wheat germ, soy bran, brewer’s yeast, and casein and another diet with wheat germ and casein as protein sources. With both diets, the viability of the egg-adult period exceeded 68%, with fertility over 338 eggs per female. A corrected biotic potential analysis gave similar values for the two diets.     

A PCR-based analysis of plant DNA reveals the feeding preferences of <Emphasis Type="Italic">Apolygus lucorum</Emphasis> (Heteroptera: Miridae)

The mirid bug Apolygus lucorum (Meyer-Dür) (Heteroptera: Miridae) is a severe pest of cotton and other crops in China. The feeding preferences of this pest are unclear due to its frequent movement among different host plants and the inconspicuous signs of its feeding. Here, we present results of a field trial that used direct observation of bug densities and a PCR-based molecular detection assay to detect plant DNA in bugs to explore relationships between A. lucorum population abundance and its feeding preference between two host plants, Humulus scandens (Loureiro) Merrill and Medicago sativa L. The field-plot samples showed that A. lucorum adults generally prefer flowering host plants. Its density was significantly higher on flowering H. scandens than on seedlings of M. sativa, and a similarly higher bug density was observed on flowering M. sativa than on seedlings of H. scandens. In the laboratory, we designed two pairs of species-specific primers targeting the trnL-F region for H. scandens and M. sativa, respectively. The detectability of plant DNA generally decreased with time post-feeding, and the half-life of plant DNA detection (DS₅₀) in the gut was estimated as 6.26 h for H. scandens and 3.79 h for M. sativa with significant differences between each other. In mirid bugs exposed to seedlings of H. scandens and flowering M. sativa, the detection rate of M. sativa DNA was significantly higher than that of H. scandens. Meanwhile, in mirid bugs exposed to seedlings of M. sativa and flowering H. scandens, a significantly higher detection rate of H. scandens DNA was found. We developed a useful tool to detect the remaining plant food species specifically from the gut of A. lucorum in the current study. We provided direct evidence of its feeding preference between H. scandens and M. sativa at different growth stages, which strongly supported a positive correlation between population abundance and feeding preference of A. lucorum on different plants under field conditions. The findings provide new insights into the understanding of A. lucorum’s feeding preference, and are helpful for developing the strategies to control this pest.     

Toxicity,membrane binding and uptake of the <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> agglutinin (SSA) in different insect cell lines

The fungal lectin purified from Sclerotinia sclerotiorum, further referred to as Sclerotinia sclerotiorum agglutinin or SSA, possesses insecticidal activity against important pest insects such as pea aphids (Acyrthosiphon pisum). This paper aims at a better understanding of its activity at cellular level. Therefore, different insect cell lines were treated with SSA. These cell lines were derived from different tissues and represent the three major orders of insects important in agriculture: CF-203 (midgut Choristoneura fumiferana, Lepidoptera), GUTAW1 (midgut, Helicoverpa zea, Lepidoptera), High5 cells (ovary, Trichoplusia ni, Lepidoptera), Sf9 (ovary cells from Spodoptera frugiperda, Lepidoptera), S2 (hemocyte, Drosophila melanogaster, Diptera), and TcA (whole body, Tribolium castaneum, Coleoptera). Although the sensitivity to SSA differs between the cell lines, SSA clearly showed toxicity in all six cell lines with median effect concentrations (EC₅₀) ranging between 9 and 42 μg/ml. An in-depth analysis of the mechanism of uptake in the cells revealed superior amounts of FITC-SSA at the membrane of CF-203 cells compared to Sf9 cells, while a similar small amount of SSA was internalized in both cell lines. Pre-incubation with the clathrin-mediated endocytosis inhibitor phenylarsine oxide inhibited the internalization of SSA into the CF-203 and Sf9 cells with a respective reduction of 6- and 1.7-fold. The data are discussed in relation to the importance of cellular uptake mechanism for SSA binding and cytotoxicity.