Diadegma insulare development is altered by Plutella xylostella reared on water‐stressed host plants

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies’ response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella (L.), reared on water‐stressed host plants (Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare (Cresson). No significant differences were observed in development of P. xylostella when reared on water‐stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non‐stressed B. napus than non‐stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non‐stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water‐stressed than non‐stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species.     

Effect of insecticides on the diamondback moth (Lepidoptera: Plutellidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae)

Studies were conducted to evaluate the toxicity of insecticides to adult Diadegma insulare (Cresson) and its host the diamondback moth, Plutella xylostella (L.). Leaf-dip and direct-dip bioassays for diamondback moth larvae and residual bioassays for adults of diamondback moth and D. insulare were used to assess mortalities. Larval mortalities at field rates were significantly higher with carbaryl, permethrin, spinosad, and tebufenozide when compared with Bacillus thuringiensis, or imidacloprid in the larval-dip bioassay 72 h after treatment. In the leaf-dip and residual bioassays, both permethrin and spinosad caused 100% mortalities to diamondback moth larvae and adults, respectively, 72 h after treatment. Of all the materials tested, only B. thuringiensis and tebufenozide were not toxic to D. insulare 24 h after treatment. Spinosad was not toxic to D. insulare 30 min after treatment. However, 100% mortality was observed 8 h after treatment.     

岛弯尾姬蜂的温室饲养

介绍了一种温室大量饲养岛弯尾姬蜂的方法。该法操作简便 ,获虫量大 ,且后代性比均衡。该饲养法为岛弯尾姬蜂的进一步研究和田间释放提供了方便     

Effects of selected insecticides on Diadegma insulare (Hymenoptera: Ichneumonidae), a parasitoid of Plutella xylostella (Lepidoptera: Plutellidae)

Effects of eight insecticides on Diadegma insulare (Cresson), a parasitoid of the diamondback moth, Plutella xylostella L., were evaluated under the laboratory conditions. The insecticides were three azadirachtin-based products (Ecozin, Agroneem and Neemix), two Bacillus thuringiensis (Bt) products (Xentari and Crymax), indoxacarb, spinosad, and λ-cyhalothrin. When D. insulare pupae were treated, none of the insecticide treatments except λ-cyhalothrin significantly reduced adult emergence, with 76-90% adults emerged from the treated pupae. In the λ-cyhalothrin treatment, only 10% D. insulare pupae produced adult wasps. Indoxacarb, spinosad, and λ-cyhalothrin caused 100% D. insulare adult mortality in 24 h in Petri dishes sprayed with insecticides in the contact bioassays, and 95.8, 100 and 95.8% adult mortality in 24 h in the ingestion bioassays, respectively. In contrast, all three azadirachtin-based insecticides and the two Bt-insecticides caused only 0-10.4% mortality of D. insulare adults after ingestion. The surviving D. insulare from ingestion treatments with Bt- and azadirachtin-insecticides parasitized 50.8-67.6% of P. xylostella larvae, respectively, compare to 72.1% for the water control. After ingesting indoxacarb, spinosad and λ-cyhalothrin mixed in honey-water, both the females and the males lived significantly shorter than those ingesting Bt- and azadirachtin-insecticides and the non-insecticide honey-water. Effects of leaf residues of indoxacarb, spinosad and λ-cyhalothrin varied significantly. The leaf residues of spinosad had the least effects on D. insulare adults, and 7- and 10-day-old residue only caused 5.6 and 7.4% mortality in 24 h, whereas 10-day-old leaf residues of indoxacarb and λ-cyhalothrin caused 40.7 and 57.4% mortality in 24 h, respectively.     

Variation in susceptibility of Diadegma insulare (Hymenoptera: Ichneumonidae) to permethrin

Six field populations of the parasitoid Diadegma insulare (Cresson) were collected from Mexico and the United States and tested for their susceptibility to permethrin by using a glass-vial residue bioassay. Significant differences existed in susceptibility, with one population significantly more susceptible than the other five. Susceptibility of D. insulare increased when they were reared for several generations in the greenhouse in the absence of selection. D. insulare was less suceptible to permethrin than the adult stage of its host, Plutella xylostella (L.), from a laboratory colony, but more susceptible than those hosts collected from a commercial field. Our data suggest that a field population of D. insulare appeared to increase its tolerance to permethrin much more slowly than P. xylostella.     

Consequences of constitutive and induced variation in the host's food plant quality for parasitoid larval development

Constitutive and induced changes in plant quality impact higher trophic levels, such as the development of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to examine how the parasitoid larva is integrated within the host during the growth process. In two experiments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host was feeding on Brussels sprout plants that were either undamaged or were previously induced by caterpillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the specialist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Parasitoid growth was more depressed on induced than on undamaged control plants, and more on wild cabbage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feeding began inducing the previously undamaged control plants, the effect of induction disappeared, revealing a temporal component of plant-parasitoid interactions. This study demonstrates how insights into the physiological aspects of host-parasitoid interactions can improve our understanding of the effects of plant-related traits on parasitoid wasps.     

半闭弯尾姬蜂寄主搜索中的学习行为

研究了半闭弯尾姬蜂寄主搜索过程中的学习行为。结果表明,成虫期之前的饲养寄主所取食的寄主植物对成蜂行为没有影响,而雌蜂早期的短暂经历可对其随后的行为反应产生显著影响,从而对已经历的植物气味表现出显著的嗜好,但这种通过学习所表现出的嗜好又可因新的经历而改变。雌成蜂不仅能对其所经历的虫伤寄主植物释放的信息化合物进行学习,而且对其所经历的寄主幼虫的信息化合物也能进行学习。     

Isoprene emission by plants is affected by transmissible wound signals

Isoprene (2-methyl 1,3-butadiene) is emitted from many plants, but the signals regulating isoprene emission are unknown. Mounting leaves in a gas exchange chamber or taking small leaf punches for biochemical analysis was found to reduce the rate of isoprene emission (Loreto & Sharkey 1993). This phenomenon was investigated by putting terminal leaflets of velvet bean (Mucuna deeringeniana L.) and kudzu [Pueraria lobaia (Willd) Ohwi.] into a gas exchange chamber and monitoring isoprene emission and photosynthesis. Lateral leaflets or remote leaves were then wounded or mechanically stimulated. The rate of isoprene emission was reduced after 1 min by up to 75% by burning a lateral leaflet with a match. Even a 7 ms^?1 (25km h^?1) wind imposed on a lateral leaflet reduced isoprene emission from the terminal leaflet by 18%. Photosynthesis rates were either unaffected by these treatments or reduced more slowly than isoprene emission rates, indicating that the effect of isoprene emission rates was not a consequence of changes in photosynthetic activity. Isoprene emission from a terminal leaflet was reduced by burning leaves above and below the monitored leaflet when on the same stem. The effect was much reduced if the burned leaf (all three leaflets) was on a different stem from the monitored leaflet. Reduction of the rate of isoprene emission was observed even when the burned leaf was 52 cm distant from the measured leaflet. Increasing the distance between the stressed leaf and the monitored leaf caused the effect to be slower and smaller. It is speculated that a signal is generated by wounding which propagates through the plant at 1.3 mm s^?1. This velocity was consistent throughout the measurements and is similar to the rate of propagation of electrical signals such as action potentials and variation potentials. The effect of the environmental stress, and particularly the wind effect, can be frequent in nature and should be considered when estimating local and regional emission of isoprene for modelling atmospheric chemistry. If leaf samples used for isoprene determination are exposed to the type of stress we investigated, isoprene emission inventories based on leaf level measurements will be underestimated.     

Root architecture of Arabidopsis is affected by competition with neighbouring plants

How roots detect and respond to the presence of neighbors is relevant to understand plant belowground interactions. The aim of the present work was to evaluate the effect of the presence of neighboring plants and the limited availability of phosphorus on root architecture. A target plant of Arabidopsis thaliana (Ler or Col) was surrounded by combinations of two individuals (Ler and Col), and subjected to different growth conditions (levels of activated charcoal (AC) and phosphorus). Both accessions consistently concentrated their roots towards the competition zone shared with a neighbor of the same accession, avoiding the side shared with the other accession. All these competition strategies disappeared when plants were limited by phosphorus or when activated charcoal was added to the growth media. Plants produced consistently fewer but longer lateral roots when activated charcoal was added to the growth media irrespective of the neighbors. Our results indicate a direct role of secondary metabolites present in the root exudates and phosphorus availability in the response of presence and identity of neighboring roots.     

The performance of an aphid parasitoid is negatively affected by the presence of a circulative plant virus

Plant viruses and aphids can interact via contest competition for plant resources and induce changes in plant physiology, which can have effects on a third trophic level. The aim of this study was to determine how the interactions between a circulative plant virus and its aphid vector may affect the performance of an endoparasitoid and how parasitism may affect the efficiency of virus transmission by its aphid vector. The timing when parasitized aphids were transferred to virus-infected lettuce leaves was critical for the performance of A. ervi. Higher parasitoid larvae mortality, longer developmental times and lower percentages of mummification were detected on viruliferous/parasitized aphid nymphs when the time lag between parasitism and exposure to the virus was less than 24 h. No significant differences were detected in virus transmission rate between parasitized and non-parasitized M. euphorbiae aphids.     

Infection of the immature stages of Diadegma semiclausum, an endolarval parasitoid of the diamondback moth, by Beauveria bassiana

Interactions between the immature stages of Diadegma semiclausum, an endolarval parasitoid of Plutella xylostella, and the fungal entomopathogen Beauveria bassiana were investigated in the laboratory. Detrimental effects of B. bassiana on D. semiclausum cocoon production and adult parasitoid emergence increased with increasing pathogen concentration and some parasitoid larvae became infected by B. bassiana within hosts. The negative impact of B. bassiana on D. semiclausum cocoon production decreased as temporal separation between parasitism and pathogen exposure increased. Adult parasitoid emergence was significantly compromised by the highest rates of B. bassiana tested even when exposure of host larvae to the pathogen was delayed until one day before predicted parasitoid cocoon formation. Parasitoid pupae were infected by the pathogen in all B. bassiana treatments which did not preclude their development.     

Effects of larval densities and the duration since larval infestation on the host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth larvae on plants

The host-searching behavior of Diadegma semiclausum, a parasitoid of diamondback moth (DBM) larvae, was studied in a wind tunnel. Wasps flew preferentially to a cabbage plant, freshly infested by 1 DBM larva, or one freshly infested by 10 DBM larvae, than to an intact plant. There was no significant difference between wasps?? responses to plants infested by different DBM larvae densities. We also found that the duration since the last infestation by 10 DBM larvae (1 or 3?days) negatively affected the attractiveness of infested plants. We also studied the time wasps spent searching for larvae on a cabbage plant (residence time). The wasps spent ca. 400?s on a plant freshly infested by 1 larva. Residence time was significantly longer (ca. 1,200?s) on a plant freshly infested by either 5 or 15 DBM larvae. Residence time of D. semiclausum on a plant freshly infested by 5 DBM larvae was significantly longer than on a previously infested plant (1 or 3?days after the last infestation). These results showed that host densities on a plant and the duration since their last infestation affected the host-searching behavior of D. semiclausum.     

Fitness-related traits in a parasitoid fly are mediated by effects of plants on its host

Plants can affect parasitoids directly, by reducing or enhancing their ability to locate hosts, or indirectly by affecting the fitness of herbivores and thus of parasitoids. Tritrophic interactions between three host plants (cucumber, tomato, sweet pepper), a polyphagous herbivore Trichoplusia ni and a generalist parasitoid Compsilura concinnata were assessed. Plants had a strong effect on T. ni larval survival, as well as on C. concinnata fitness-related traits: cucumber-fed hosts yielded parasitoids with shorter larval development time and females had heavier pupal weights than parasitoids from host larvae that were fed tomato. Furthermore, C. concinnata was more efficient at finding cucumber-fed than tomato-fed T. ni . These results suggest that C. concinnata has different efficiency and potential as a biocontrol agent on the different crops. This highlights the importance of assessing tritrophic interactions in systems where an inundative biological control agent may be released against generalist targets on more than one crop plant.     

Occurrence of Diadegma semiclausum,a parasitoid of diamondback moth in lowlands of Syria

The parasitoid, Diadegma semiclausum (Hymenoptera: Ichneumonidae) is one of the most effective parasitoids of diamondback moth (DBM) in the highlands (> 1600 m above sea level) of Asia. A Diadegma population from the lowland areas of Homs, Syria (about 203–487 m above sea level) was examined to determine if it differs at the species-level from the D. semiclausum and other Diadegma populations present in different countries using molecular diagnostic tools. Phylogenetic analysis based on the neighbor-joining method using the mitochondrial cytochrome oxidase I (COI) and the nuclear internal transcribed spacer 2 (ITS2) sequences grouped the Homs (Syria) Diadegma population with D. semiclausum populations from other countries. The results suggest that D. semiclausum occurs in the lowland conditions in Homs (Syria), where the temperature is higher. The Homs (Syria) strain did not show any variations in the parasitism when the parasitized host (DBM) larvae were exposed to varying temperatures for 24 h. It could not survive when the parasitized DBM larvae were continuously reared at 35 °C; however it inflicted significantly higher parasitism when the parasitized DBM larvae were reared at day and night temperatures of 35 °C and 20 °C, respectively. Preliminary results indicate that the D. semiclausum strain from Homs (Syria) possesses some level of heat tolerance, which could be exploited for successful management of DBM in the tropical lowlands.     

Fitness consequences of ovicide in a parasitoid wasp

Ovicide, superparasitism and host rejection are alternative reproductive tactics facing female parasitoid wasps encountering an already-parasitized host. Superparasitism is simply the addition of an egg or a clutch of eggs by the secondary parasitoid, but under ovicide the primary clutch is removed or destroyed. Host rejection occurs if the wasp leaves without laying a clutch. The ectoparasitoid Laelius pedatus (Say) (Hymenoptera: Bethylidae) performs ovicide in this situation. Clutch manipulation experiments show that secondary clutches suffer high mortality in competition with primary clutches, which increases with increasing time delay between clutches. Primary clutches however suffer little in competition with secondary clutches, even if there is minimal time delay between clutches. These data suggest that the offspring of ovicidal females are substantially fitter than the offspring of superparasitizing females. Handling time and clutch size do not differ significantly between first (sole) parasitoids and second (ovicidal) parasitoids. The same is true for offspring survival and development time. However, offspring of second females are slightly smaller. This suggests that parasitized and unparasitized hosts are resources of similar quality when ovicide is performed. These data strongly support the predictions of evolutionary models of ovicide. They may also give some insight into the taxonomic distribution of ovicide in parasitoids.     

Anti-tumor activity of chemokine is affected by both kinds of tumors and the activation state of the host's immune system: implications for chemokine-based cancer immunotherapy

In this study, we screened the anti-tumor activity of murine chemokines including CCL17, CCL19, CCL20, CCL21, CCL22, CCL27, XCL1, and CX3CL1 by inoculating murine B16BL6, CT26, or OV-HM tumor cells, all of which were transfected with chemokine-expressing fiber-mutant adenovirus vector, into immunocompetent mice. A tumor-suppressive effect was observed in mice inoculated with CCL19/B16BL6 and XCL1/B16BL6, and CCL22/OV-HM showed considerable retardation in tumor growth. In the cured mice inoculated with CCL22/OV-HM, a long-term specific immune protection against parental tumor was developed. However, we were unable to identify the chemokine that had a suppressive activity common to all three tumor models. Furthermore, an experiment using chemokine-transfected B16BL6 cells was also performed on mice sensitized with melanoma-associated antigen. A drastic enhancement of the frequency of complete rejection was observed in mice inoculated with CCL17-, CCL19-, CCL22-, and CCL27-transfected B16BL6. Altogether, our results suggest that the tumor-suppressive activity of chemokine-gene immunotherapy is greatly influenced by the kind of tumor and the activation state of the host's immune system.     

Nitrogen uptake of plants affected by windbreaks

Summary The present study was carried out with the windbreaks to determine the effect of wind protection on the uptake of nitrogen by plants. The results of the analysis clearly show that nitrogen uptake is favourably affected by the windbreaks. Nitrogen uptake by the plants in the protected zone at Altona was 52% higher as compared to the unprotected zone. The plants at both the optimal protected and less protected areas at Newton absorbed similar amounts of nitrogen. The increased uptake of nitrogen in the protected zone at Altona was due to the windbreak which favourably influenced the temperature and the evapotranspiration rate. This resulted in the better growth and yield of plants.

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Sommaire La présente étude fut faite à l'aide de brise-vents afin de determiner l'effect de protection du vent en rapport à l'ingestion de l'azote par les plantes. Les résultats de l'analyse montrent clairement que l'ingestion d'azote est favourablement affectée par les brise-vents. L'ingestion d'azote par les plantes de la zone protégée d'Altona fut 52% plus haute que celle de la zone non-protégée. Les plantes, aux endroits de protection maximale et de moindre protection de Newton, ont absorbé des quantités semblables d'azote. L'augmentation de l'ingestion en azote dans la zone protégée d'Altona fut due à l'effect des brisevents qui ont influen?é favourablement la température et le taux d'évapotranspiration. Ceci donna finalement une meilleure croissance et une meilleure productivité des plantes.

     

Aggregation in field parasitoid populations: foraging time allocation by a population of Diadegma (Hymenoptera, Ichneumonidae)

ABSTRACT.

• 1 A field study was made of foraging time allocation by a population of parasitic wasps, Diadegma spp. (Ichneumonidae), to plants containing different densities of their hosts, the caterpillars of Plutella xylostella (L.).
• 2 The parasitoid population exhibited a clear aggregative response, spending more total time on higher density patches, which probably resulted from wasps making more and longer visits to these densities.
• 3 Despite this aggregation, positive density dependent parasitism was not found. The functional response of the Diadegma population exhibited an upper asymptote at high host densities, probably due to an increase in the proportion of time spent handling hosts, which countered the effect of aggregation.
• 4 While Diadegma may select and forage preferentially on plants with higher host density, they do not exhibit the tendency, predicted by some optional foraging models, to exploit progressively less profitable plants during a foraging bout. Some factors affecting patterns of parasitoid foraging in the field are discussed.