Aphids Facing Their Parasitoids: A First Look at How Chemical Signals May Make Higher Densities of the Pea Aphid Acyrthosiphon pisum Less Attractive to the Parasitoid Aphidius ervi

Herbivore-induced plant volatiles constitute the first indicators of insect host presence, and these can affect the foraging behavior of their natural enemies. The density of insect hosts may affect the nature and concentration of these plant-induced volatiles. We tested the impact of infestation density (low, intermediate, and high) of the pea aphid, Acyrthosiphon pisum (Homoptera: Aphididae), feeding on the broad bean Vicia faba, on the attractiveness of the parasitoid Aphidius ervi (Hymenoptera: Braconidae), using a Y-tube olfactometer (infested vs. non-infested plants). The emitted volatile compounds from both infested and non-infested plants were collected and identified. In addition, two series of experiments were carried out to test the impact of the presence of a conspecific female parasitoid within the aphid/plant complex on the attractiveness to other females. Parasitoids were significantly more attracted to the plants with low and intermediate aphid infestation levels. The volatile blend composition of the infested plants changed in relation to aphid density and may explain the low attraction of parasitoids toward high aphid density. The presence of conspecific females on the aphid patch had no apparent impact on the behavioral choices of other parasitoid females. Our study adds a new aspect to understanding plant–aphid–parasitoid interactions, including the possibility that aphids may manipulate chemical cues of host plants affecting the orientation of parasitoids.

Competitive Capacity of Native Species From the Carajás National Forest, Brazil

The present research had the objective to use the factor analysis in the evaluation of the competitive capacity of three native species from the Carajás National Forest in competition with different plant densities of the Urochloa brizantha grass. The experiment was conducted in a greenhouse and consisted in planting pots with the native species Bauhinia longipedicellata, Mimosa acutistipula and Solanum crinitum in competition with the exotic grass Urochloa brizantha. The exotic grass was established at densities ranging from 1 to 5 plants per pot, composing a 3 × 5 factorial arrangement with four replications that were delineated completely at random. Data were submitted to factor analysis for further analysis of variance and Tukey’s test at a 0.05 level of significance with the extracted factors. The effects of U. brizantha densities were evaluated by regression analysis. Out of the four extracted factors, three could be interpreted and were defined as vegetative growth index, infestation density index and physiological quality index. The Solanum crinitum species was slightly greater than the others in terms of vegetative growth rate and physiological quality. Generally speaking, native species maintain their vegetative growth in competitive conditions with up to two Urochloa brizantha plants; above that, the vegetative growth index tends to zero, while the infestation density index becomes positive.

Reproduction abilities of Ips typographus (L.) (Coleoptera: Curculionidae, Scolytinae) in the stands damaged by the wind in 2013 in the Kościeliska Valley (Tatra National Park)

At the end of 2013, strong wind destroyed spruce stands on large areas of Kościeliska Valley in Tatra Mts. in Poland. In 2015–2017, 304 bark samples were collected from 106 spruces; 25 cm × 25 cm large samples were taken from 2 or 4 sections of infested trees in July/August each year. The infestation density, sex ratio, length of maternal galleries, number of progeny and impact of natural enemies were recorded. The infestation density in individual years was 0.79–0.86 mating chambers per dm2, the average length of maternal gallery (55.2–56.6 mm) did not differ between years, The average number of progeny per female from 3-year pooled data was 18.22, the highest in 2015 (27.4) then collapsed to 15.5–16.8. The gallery systems with 2 females, in which the reproduction success was the highest, dominated (62.6%). The frequency of parasitoids or entomopathogens was very low (2–20% mortality rate in 19 bark samples). Possible reasons of relatively low reproduction success regardless generally favourable breeding conditions and its collapse after first year, such as high infestation density and low survival rate of larvae because of climatic conditions (drought), are discussed. Taking into account the described population features, very intense tree mortality and mechanisms known from the other wind events, further development of the outbreak can be expected in this area.

Occurrence of Ips typographus (L.) after wind damage in the Kościeliska Valley of the Tatra National Park

At the end of 2013, Norway spruce stands in the area of the Tatra National Park were severely damaged by strong storms especially in the Kościeliska Valley region. In the following spring of 2014, a survey recording the occurrence of the spruce bark beetle Ips typographus (Coleoptera, Curculionidae, Scolytinae) was initiated in order to describe the dynamics of beetle reproduction in relation to protection measures executed in wind-damaged stands. Ten research plots with 20 trees each were established in a socalled active protection zone, where the broken and fallen trees had been processed and removed in 2014, and in a passive protection zone, where no actions were taken, and the dynamics of Norway spruce mortality due to bark beetle infestation including quantitative parameters (infestation density, sex ratio of beetle populations) were examined. The entomological analyses were performed on 25 × 25 cm large bark samples taken from four (active zone) or two (passive zone) tree sections. In the first year of the survey, no infested standing trees were recorded on the plots and the colonisation of fallen and broken trees was very weak. In the second year (2015), infestations appeared in larger numbers on the plots with passive compared to active protection but the infestation density was 0.89 mating chambers per 1 dm2 regardless of the protection status. In the third year (2016), most of the remaining living spruces had been infested with a mean density of 0.82 m.ch. per 1 dm2. In 2015, the proportion of females in the beetle population was 65.8% being higher in the active (68.4%) than the passive (64.0%) protection zone, while in 2016 the proportion was 63.5% and in this case slightly higher in the passive protection zone (63.9% as compared to 63.2%). These results are in accordance with patterns observed in wind-damaged Norway spruce stands of other areas in Poland and Europe and demonstrate the usefulness of forest management procedures in mitigating I. typographus outbreaks.

Ecological data of Lepidosaphes gloverii (Hemiptera: Diaspididae) in Greece

In June 2001 the scale Lepidosaphes gloverii (Packard) (Hemiptera: Diaspididae) was found on orange trees in Peloponnesus, Gastouni area, (Southwestern Greece). From the day it was first recorded until August 2003 observations on orange trees were held both in field and laboratory, concerning the biology and ecology of this scale. L. gloνerii infests mainly the upper surface of the leaves and the fruits and less the shoots of the tree. During the period April to August 2002 the scale completed 3 overlapping generations. Female fecundity ranged between 32 and 57 eggs. Chilocorus bipustulatus (L.) (Coleoptera: Coccinellidae) and Rhyzobius lophanthae Blaisdell (Coleoptera: Coccinellidae) predators were found to feed upon this scale. In Ju1y 2002 a mass release of those predators took place on infested orange trees. To assess the action of these predators, observations were conducted in both field (by shaking the branches of the trees and counting the number of the predators) and laboratory (by counting the predated scales found on leaves). The release of predators contributed to the decrease of infestation density of trees. C. bipustulatus developed significantly higher populations than R. lophanthae.

Weed Occurrence in Sugarcane as Function of Variety and Ground Straw Management1

ABSTRACT This study aims to verify the effect of crop varietal architecture and straw removal from planting rows in the occurrence of weeds in sugarcane and infer about the sustainability of the production system with no herbicide application. The experiment was established in 2011 in a randomized block design with split plots and four replications. Main plots were varieties IACSP95 5000 and SP91 1049. In the sub-plots there the straw removal was allocated (evenly scattered in the area, or concentrated in inter-rows). Assessments were conducted in 2012 and 2013 and the absolute levels of infestation, density, frequency and dominance of weed species were obtained. Areas were intra-characterized by the coefficients of Simpson and Shannon-Weiner and sustainability inferred by the SEP coefficient. Areas were grouped by the similarity coefficient of Jaccard. Other factors besides leaf architecture were more significant for level of infestation. Treatments with straw removal from planting rows were more infested than those with evenly scattered straw. In the second year of cultivation, those species most adapted to the system increased their importance value. Wild poinsettia was the dominant weed in all treatments, deserving attention from pre-planting on, to reducing its occurrence in the soil seed bank. Species diversity was higher where straw was evenly scattered due to the occurrence of species other than wild poinsettia. Sustainability was reduced from the first to the second year, indicating that only cultural practices are not enough, even with high shading provided by crop and straw production, demanding herbicides.