SciCombinator

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Journal: Environmental entomology

27

Leishmania infantum-the causal agent of human and canine leishmaniasis in the Mediterranean basin-remains the most important of the phlebotomine sand fly-borne pathogens in the area. However, information on phlebotomine sand flies in certain European regions remains scarce and consequently epidemiological modeling, risk prediction, and disease control are difficult. Thus, we aimed to investigate the presence and distribution of phlebotomine sand fly vectors of L. infantum in an endemic region of continental Mediterranean Spain. Climatically stratified trapping of phlebotomine sand flies was performed over 39 points in south-central Spain. Later on, the effect of ecogeographical variables-geography trend, climate, habitat, and hosts-over the abundance of the predominant species-Phlebotomus perniciosus Newstead, 1911-was analyzed. Polymerase chain reaction was performed over pools of the captured species to search for L. infantum DNA. There were 152 phlebotomine sand flies (142 Ph. perniciosus and 10 Phlebotomus ariasi Tonnoir, 1921) captured. Model results showed that Ph. perniciosus abundance is expected to be higher in warm agricultural areas within the study region in agreement to previous findings in other climatic regions. Molecular analyses revealed the presence of L. infantum DNA in pools from locations in the study region displaying the highest abundance of phlebotomine sand flies. These findings suggest that along mainland Spain, warm agricultural landscapes are more prone to harbor higher abundances of Ph. perniciosus and account for a higher risk of exposure to L. infantum.

Concepts: DNA, Polymerase chain reaction, Climate, Leishmaniasis, Leishmania, Phlebotominae, Canine leishmaniasis, Phlebotomus

27

We examined the extent to which verbenone, a bark beetle antiaggregation pheromone, interrupted the semiochemical-based attraction of ambrosia beetles. Field trapping studies conducted in Ohio showed that a verbenone dispenser with a release rate of 50 mg/d at 25°C reduced the attraction of Anisandrus sayi Hopkins, Euwallacea validus (Eichhoff), Hypothenemus dissimilis (Zimmermann), Xylosandrus germanus (Blandford), and Xyleborinus saxesenii (Ratzeburg) to ethanol-baited traps. A verbenone dispenser attached to ethanol-injected Magnolia virginiana L. trap trees deployed in Ohio also reduced ambrosia beetle attacks compared to trap trees without a verbenone dispenser. Subsequent field trials demonstrated a direct relationship between distance from a verbenone dispenser and ambrosia beetle attacks on trap trees in Ohio in 2011 and 2012 and Tennessee in 2012, but not in Tennessee and Virginia in 2011. Assessment of the influence of verbenone on the probability of attacks above a density threshold found that although attacks occurred on trap trees regardless of their proximity to a verbenone dispenser, the higher density of attacks per tree occurred on trap trees farthest away from the verbenone source in Ohio and Tennessee. Verbenone alone could be somewhat useful for discouraging ambrosia beetle attacks on individual trees or on a small spatial scale, but deployment of verbenone might be most effective when integrated as part of a “push-pull” strategy.

Concepts: Beetle, Curculionidae, Magnolia, Virginia, Bark beetle, Ambrosia beetle, Xyleborini, Mycangium

27

Herbicides are the most commonly applied pesticides in agroecosystems, and therefore pose potentially significant ecotoxicological risks to plants and insects. Glyphosate is the most common herbicide worldwide, and glyphosate-resistant weeds are quickly becoming serious challenges in some agroecosystems. Because of this resistance epidemic and the recent development of crops with resistance to dicamba or 2,4-D, herbicide-use patterns are likely to change. Presently, dicamba and 2,4-D cause most herbicide-drift damage to nontarget plants despite limited agricultural usage, but the effects of these synthetic auxin herbicides on insects have been poorly explored. To understand the influence of dicamba on insects, we applied several sublethal, drift-level rates of dicamba to soybean, Glycine max L., and Carduus thistle, and measured growth and survival of Helicoverpa zea (Boddie) and Vanessa cardui (L.) larvae, respectively. For thistle, we measured percent nitrogen content before and after dicamba application. We also performed direct toxicity bioassays on the two caterpillar species with several rates of dicamba. Dicamba was not directly toxic to larvae of either species, and H. zea showed no negative effects when feeding on soybeans dosed with dicamba. We did, however, detect significant negative, indirect effects of higher rates of dicamba on V. cardui larval and pupal mass, total nitrogen of thistles post application, and thistle biomass in the presence of V. cardui larvae. Notably, thistle biomass was not related to dicamba dose in absence of larvae. Our results indicate that dicamba can indirectly influence the performance of some caterpillar species, possibly by altering plant nutritional content.

Concepts: Agriculture, Plant, Larva, Soybean, Maize, Lepidoptera, Caterpillar, Herbicide

27

We present a population model of the insect Scaphoideus titanus Ball, the leafhopper vector of Flavescence Dorée phytoplasma in Vitis vinifera L. The model accounted for the stage-dependent S. titanus life cycle rates and timing, and vineyard settings such as surface area, plant density, and sampling characteristics. The model parameters were estimated against 13 independent cases of population counting in both laboratory and field conditions, and returned a correlation coefficient in the range 86.4 to 99.1% with residuals in the range 3.5 to 26.3%. A statistical parametric analysis showed that the standard deviation of life cycle rates generally varied more than the one resulting from timing parameters. However, a stochastic sensitivity analysis showed that S. titanus dynamics were more susceptible to variations in timing than rate parameters. Analysis of scenarios of insecticide suppression efficiency and timing showed that S. titanus presence could be optimally controlled by a combination of suppression efficiency and timing. These results were instrumental to understand in which specific aspect of S. titanus life cycle could pest management operations be most effective to reduce S. titanus presence in vineyards, and possibly reduce the risk of Flavescence phytoplasma spread.

Concepts: Statistics, Vitis vinifera, Deviation, Wine, Vitis, Viticulture, Parametric statistics, Winemaking

27

Mutualism is a common and important ecological phenomenon characterized by beneficial interaction between two species. Red imported fire ants, Solenopsis invicta Buren, tend honeydew-producing hemipteran insects and reduce the activity of these insects' enemies. Ant-hemipteran interactions frequently exert positive effects on the densities of hemipterans. We tested the hypothesis that ant tending can increase the densities of the mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), and reduce the densities of the mealybug’s predatory and parasitic enemies, the lady beetle, Menochilus sexmaculata Fabricius (Coleoptera: Coccinellidae), and the parasitoid wasp, Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae). We found that more ants foraged on mealybug-infested hibiscus plants than on mealybug-free plants. The number of foraging ants on plants infested with high densities of mealybugs (62.5 ants per plant) was nearly six times that on mealybug-free plants (10.2 ants per plant). Experiment results showed that ant tending significantly increased the survival of mealybugs: if predatory and parasitic enemies were present, the survival of mealybugs tended by fire ants was higher than that in the absence of tending ants. Furthermore, this tending by fire ants significantly decreased the survival of lady beetle larvae. However, no apparent effect was observed on the survival of parasitoid.

Concepts: Insect, Symbiosis, Beetle, Ant, Hymenoptera, Parasitoid, Aphid, Mutualism

26

Subterranean termites are extremely vulnerable to desiccation, and high moisture makes their habitat and food favorable for survival and colony growth. Although there is a general perception that termites can manipulate moisture, documentation is surprisingly scanty with regard to how termites transport water and the factors that impact it. There has been no study of water transfer by Coptotermes formosanus Shiraki, a notoriously invasive termite in the southern United States. We conducted a study to determine if C. formosanus transfers water. Bioassays using arenas with a dry food source connected to a moist substrate by either a short tube (10 cm) or a long tube (100 cm) were conducted. Three moistened substrate types were tested to see how they impacted water transfer. In addition, workers and soldiers sampled from a moist sand substrate were dissected to determine water sac volumes for possible transfer of water to wood. The results indicated that some water transfer is achieved by the evacuation of water sacs. However, moist soil was also moved to increase humidity. When termites had use of moist silty clay, wood moisture gain increased significantly in both 10 and 100 cm tubes. As tube distance increased, moisture to the more distant food source decreased. Workers had the largest water sacs, though soldiers appear to contribute in water transfer via water sacs as well. Water transfer and its implications are discussed.

Concepts: Insect, Orders of magnitude, Cellulose, Cockroach, Termite, Rhinotermitidae, Termites, Formosan subterranean termite

26

Ophraella communa LeSage (Coleoptera: Chrysomelidae) is an important biological control agent of the common ragweed, Ambrosia artemisiifolia L., in China. Development and fecundity of O. communa, and hatch rate of progeny eggs were studied at five photoperiods (8:16, 10:14, 12:12, 14:10, and 16:8 [L:D] h). The highest survival rate of eggs was 92% at the photoperiod of 16:8 (L:D) h, and those of both larvae and pupae were observed at the photoperiod of 14:10 (L:D) h (85 and 96%). The shortest developmental durations of larvae and pupae were observed at photoperiods of 14:10 and 16:8 (L:D) h. Fecundity was 1,159-1,976 eggs per female from photoperiods of 8:16 to 16:8 (L:D) h. The hatch rates of progeny eggs were 67-92% from photoperiods of 8:16 to 16:8 (L:D) h, and photoperiods did not affect developmental duration of progeny eggs. The intrinsic rate for increase ®, the net reproductive rate (R0), and the finite rate of increase (λ) reached the maximum values at 16:8 (L:D) h (0.2219 d(-1), 721 hatched eggs and 1.2484 d(-1), respectively) and 14:10 (L:D) h (0.2133 d(-1), 605.6 hatched eggs and 1.2378 d(-1), respectively). Their minimum values were observed at the photoperiod of 8:16 (L:D) h, which were 0.1731 d(-1), 212.2 hatched eggs and 0.1890 d(-1), respectively. The shortest T value was 29.7 d at a photoperiod of 16:8 (L:D) h and the longest was 31.4 d at a photoperiod of 12:12 (L:D) h. Our study shows that O. communa could survive and reproduce successfully at different photoperiods, thus may expand its distribution to regions with different photoperiods.

Concepts: Insect, Developmental biology, Beetle, Biological pest control, Common cold, Ragweed, Ambrosia artemisiifolia, Ambrosia

26

To develop safe and effective methods to protect whitebark pines, Pinus albicaulis Engelmann, and limber pines, Pinus flexilis James, from attack by mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), we compared verbenone and verbenone plus green leaf volatiles (GLVs) for prevention of beetle attack. We used two strategies: area-wide protection where semiochemical-releasing flakes are dispersed over the forest floor, and individual tree tests where flakes are applied to tree trunks. The area-wide bioassays were conducted by applying verbenone- and GLV-releasing flakes without stickers to the forest floor on 0.81-ha plots dominated by whitebark pines in the State of Washington with four replicates. We conducted individual tree bioassays by applying the same formulations with stickers to whitebark and limber pines in Montana and Colorado, respectively. In all three situations, both verbenone-alone and verbenone plus GLVs significantly increased the proportion of trees escaping mass attack by beetles, but the two formulations were not significantly different from one another. Despite a lack of significance at a Bonferroni-adjusted α = 0.05, adding GLVs gave slightly greater absolute levels of tree protection in most cases. Monitoring traps placed in the area-wide treatments in Washington showed similar outcomes for numbers of beetles trapped: both treatments had significantly fewer beetles than controls, and they were not significantly different from one another. At peak flight, however, plots with GLVs combined with verbenone had roughly 40% fewer beetles than plots with verbenone alone. GLVs are considerably cheaper than verbenone, so tests of higher application rates may be warranted to achieve enhanced tree protection at reasonable cost.

Concepts: Beetle, Pine, Pinus classification, Curculionidae, Pinus, Mountain pine beetle, Bark beetle, Tree line

26

Potato virus Y (PVY) is an economically important and reemerging potato pathogen in North America. PVY infection reduces yield, and some necrotic and recombinant strains render tubers unmarketable. Although PVY(O) is the most prevalent strain in the United States, the necrotic and recombinant strains PVY(NTN) and PVY(N:O) are becoming more widespread. Infection rates in aphid-inoculated (Myzus persicae (Sulzer)) and mechanically inoculated plants were compared across two potato genotypes (‘Yukon Gold’ and A98345-1), three PVY strains (PVY(O), PVY(N:O), and PVY(NTN)), and two growth stages at inoculation (pre- and postflowering). Susceptibility of genotypes was measured as infection rate using a double-antibody sandwich-enzyme-linked immunosorbent assay; virus titer and tuber mass also were recorded from the infected plants. Yukon Gold generally was more susceptible than A98345-1 to all three PVY strains, especially following mechanical inoculation. Within genotypes, Yukon Gold was most susceptible to PVY(O) and A98345-1 was most susceptible to PVY(N:O). Plants exhibited age-based resistance, with both genotypes showing higher susceptibility at the pre- than postflowering stage. The overall ranking pattern of virus titer in infected plants was PVY(O) > PVY(NTN) > PVY(N:O); across all three strains, infected Yukon Gold had higher titer than infected A98345-1 plants. Yukon Gold plants had lower tuber mass than A98345-1 when infected, and there were differences between the two inoculation methods in regard to tuber mass for the three stains. The results showed differences in infection response between inoculation methods and as a function of genotype, strain, inoculation stage, and their interactions. These factors should be considered when screening genotypes for resistance.

Concepts: DNA, Potato, Hemiptera, Aphididae, Potato virus Y, Myzus persicae, Potato leafroll virus

25

The coconut rhinoceros beetle, Oryctes rhinoceros L., is a serious pest of coconut and other palms throughout Southeast Asia and on several Pacific Islands. Adults damage and sometimes kill palms when they bore into the crown to feed. In contrast, larvae feed only on dead plant material at breeding sites. Typically, coconut rhinoceros beetle populations are controlled with a combination of biocontrol, pheromone traps, and breeding site removal. A field trial was performed at two locations on Guam to test the feasibility of using the Judas technique, releasing radio-tagged adults to discover cryptic breeding sites, for potential coconut rhinoceros beetle control. Of 33 radio-tagged beetles that were released, 19 were successfully tracked to landing sites, 11 of which were considered to be active or potential breeding sites, in five different microhabitats. The remaining 14 beetles were lost when they flew beyond the range of receivers. Only one of the radio-tagged beetles was caught in the numerous pheromone traps present at the release sites. Percent emergence weight (%EW, ratio of current/emergence weight) varied significantly by the microhabitat to which coconut rhinoceros beetles were tracked. When microhabitats were further grouped, the difference in mean %EW between the arboreal (74 ± 2%) and the soil-associated (82 ± 3%) groups were found to be highly significant. The %EW for coconut rhinoceros beetles that were successfully located (78 ± 2%) and those that were lost (72 ± 2%) also differed significantly. Radio-tracking coconut rhinoceros beetles shows promise as a method to identify cryptic breeding sites, which could then be treated, removed, or destroyed.

Concepts: Insect, Larva, Beetle, Scarabaeidae, Japanese rhinoceros beetle, Dynastinae, Rhinoceros beetle, Xylotrupes ulysses