S.T.E. Lommen

Is the Recent Decrease in Airborne Ambrosia Pollen in the Milan Area Due to the Accidental Introduction of the Ragweed Leaf Beetle Ophraella Communa

This study aims to determine whether a significant decrease in airborne concentrations of Ambrosia pollen witnessed in the north-west of the Province of Milan in Northern Italy could be explained by environmental factors such as meteorology, or whether there is evidence to support the hypothesis that the decrease was related to the presence of large numbers of the oligophagous Ophraella communa leaf beetles that are used as a biological control agent against Ambrosia in other parts of the world. Airborne concentrations of Ambrosia, Cannabaceae and Urticaceae pollen data (2000–2013) were examined for trends over time and correlated with meteorological data. The amount of Ambrosia pollen recorded annually during the main flowering period of Ambrosia (August–September) was entered into linear regression models with meteorological data in order to determine whether the amount of airborne Ambrosia pollen recorded in 2013 was lower than would normally be expected based on the prevailing weather conditions. There were a number of significant correlations between concentrations of airborne Ambrosia, Cannabaceae and Urticaceae pollen, as well as between airborne pollen concentrations and daily and monthly meteorological data. The linear regression models greatly overestimated the amount of airborne Ambrosia pollen in 2013. The results of the regression analysis support the hypothesis that the observed decrease in airborne Ambrosia pollen may indeed be related to the presence of large numbers of O. communa in the Milan area, as the drastic decrease in airborne Ambrosia pollen in 2013 cannot be explained by meteorology alone.

It is time to bridge the gap between exploring and exploiting: prospects for utilizing intraspecific genetic variation to optimize arthropods for augmentative pest control – a review

Intraspecific genetic variation in arthropods is often studied in the context of evolution and ecology. Such knowledge, however, can also be very usefully applied to biological pest control. Selection of genotypes with optimal trait values may be a powerful tool to develop more effective biocontrol agents. Although it has repeatedly been proposed, this approach is still hardly applied in the current commercial development of arthropod agents for pest control. In this perspective study, we call to take advantage of the increasing knowledge on the genetics underlying intraspecific variation to improve biological control agents. We argue that it is timely now because at present both the need and the technical possibilities for implementation exist, as there is (1) increased economic importance of biocontrol, (2) reduced availability of exotic biocontrol agents due to stricter legislation, and (3) increased availability of genetic information on non‐model species. We present a step‐by‐step approach towards the exploitation of intraspecific genetic variation for biocontrol, outline that knowledge of the underlying genetic mechanisms is essential for success, and indicate how new molecular techniques can facilitate this. Finally, we exemplify this procedure by two case studies, one focussing on a target trait – offspring sex ratio – across species of hymenopteran parasitoids, and the other on a target species – the two‐spot ladybird beetle – where wing length and body colouration can be optimized for aphid control. With this overview, we aim to inspire scientific researchers and biocontrol agent producers to start collaborating on the use of genetic variation for the improvement of natural enemies.

A follow-up study examining airborne Ambrosia pollen in the Milan area in 2014 in relation to the accidental introduction of the ragweed leaf beetle Ophraella communa

The North American invasive alien Ambrosia artemisiifolia L. (common or short ragweed) is considered to be an important weed in agriculture and source of highly allergenic pollen (Smith et al. 2013; Essl et al. 2015 references therein) in many parts of the world, including Europe. The oligophagous leaf beetle Ophraella communa LeSage 1986 (Coleoptera: Chrysomelidae) preferably feeds from A. artemisiifolia, and is successfully used as a biological agent to control this weed in China (Zhou et al. 2014). It can prevent plants from producing seeds and pollen when it kills them before flowering. In 2013, this beetle was found to have accidentally established in Southern Switzerland and Northern Italy, with high incidence and densities in the Milan area Muller Scharer et al. 2014). The map showing the presence of the beetle has now been updated for 2014 (Fig. 1). We have previously shown, using linear regression models, that the exceptionally low amounts of airborne Ambrosia pollen observed in the Milan area in 2013 could not be explained by meteorology in that year. We therefore suggested that the decrease might be related to the presence of large numbers of O. communa (Bonini et al. 2015)

Development of a wingless morph in the ladybird beetle, Adalia bipunctata

SUMMARY Many taxa of winged insects have independently lost the ability to fly and often possess reduced wings. Species exhibiting natural variation in wing morphology provide opportunities to investigate the genetics and developmental processes underlying the evolution of alternative wing morphs. Although many wing dimorphic species of beetles are known, the underlying mechanisms of variation are not well understood in this insect order. Here, we examine wing development of wild type and natural wingless morphs of the two‐spot ladybird beetle, Adalia bipunctata. We show that both pairs of wings are distally truncated in the wingless adults. A laboratory population of the wingless morph displays heritable variation in the degree of wing truncation, reflecting reduced growth of the larval wing discs. The coexistence of variable wingless morphs supports the idea that typical monomorphic wingless insects may be the result of a gradual evolution of wing loss. Gene expression patterns in wing discs suggest that the conserved gene network controlling wing development in wild‐type Adalia is disrupted in the dorsoventral patterning pathway in the wingless morphs. Previous research on several species of ant has revealed that the anteroposterior wing patterning pathway is disrupted in wingless workers. Future investigations should confirm whether interruptions in both taxa are limited to the patterning pathways found thus far, or whether there are also shared interruption points. Nevertheless, our results highlight that diverse mechanisms of development are likely to underlie the evolution of wingless insects.

Releases of a natural flightless strain of the ladybird beetle Adalia bipunctata reduce aphid-born honeydew beneath urban lime trees

Aphids can cause major environmental problems in urban areas. One important problem is the annual outbreaks of lime aphid, Eucallipterus tiliae (L.) (Hemiptera: Aphididae), which spoil the surroundings of lime trees by depositing honeydew. To date no environmentally friendly method has been demonstrated to yield effective control of lime aphids. Attempts are made in some cities to control lime aphids by releasing larvae of the native two-spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae). However, it is known that adult ladybird beetles disperse soon after release, and there is little indication they provide control of the aphids. Here, we demonstrate experimentally that releases of a flightless strain of A. bipunctata, obtained from natural variation in wing length, can reduce the impact of honeydew from lime aphid outbreaks on two species of lime in an urban environment. Both larvae and adult beetles were released, and we discuss the contribution of the flightless adults to the decline in honeydew.

Explaining variability in the production of seed and allergenic pollen by invasive Ambrosia artemisiifolia across Europe

To better manage invasive populations, it is vital to understand the environmental drivers underlying spatial variation in demographic performance of invasive individuals and populations. The invasive common ragweed, Ambrosia artemisiifolia, has severe adverse effects on agriculture and human health, due to its vast production of seeds and allergenic pollen. Here, we identify the scale and nature of environmental factors driving individual performance of A. artemisiifolia, and assess their relative importance. We studied 39 populations across the European continent, covering different climatic and habitat conditions. We found that plant size is the most important determinant in variation of per-capita seed and pollen production. Using plant volume as a measure of individual performance, we found that the local environment (i.e. the site) is far more influential for plant volume (explaining 25% of all spatial variation) than geographic position (regional level; 8%) or the neighbouring vegetation (at the plot level; 4%). An overall model including environmental factors at all scales performed better (27%), including the weather (bigger plants in warm and wet conditions), soil type (smaller plants on soils with more sand), and highlighting the negative effects of altitude, neighbouring vegetation and bare soil. Pollen and seed densities varied more than 200-fold between sites, with highest estimates in Croatia, Romania and Hungary. Pollen densities were highest on arable fields, while highest seed densities were found along infrastructure, both significantly higher than on ruderal sites. We discuss implications of these findings for the spatial scale of management interventions against A. artemisiifolia.

Defoliation of common ragweed by Ophraella communa beetle does not affect pollen allergenicity in controlled conditions

Abstract Ragweed allergy is one of the primary causes of seasonal allergies in Europe and its prevalence is expected to rise. The leaf beetle Ophraella communa, recently and accidentally established in N-Italy and S-Switzerland, represents a promising approach to control ragweed, but negative side effects should be excluded before its use. Since biotic and abiotic stresses are known to influence the allergenicity of pollen, we set out to assess the effect of sub-lethal defoliation by O. communa on the quantity and quality of ragweed pollen. Seventeen sister pairs (including six clones) of ragweed plants were grown in controlled conditions. One of each pair was exposed to O. communa as soon as the plant started to produce reproductive structures. After 10 weeks of exposure, plant traits were measured as a proxy for pollen quantity. Pollen quality was assessed by measuring its viability and allergenicity. Generally, plants produced very few male flowers and little amount of pollen. Damage by the beetle was severe with most of the leaf tissue removed, but no treatment effect was found on any of the quantitative and qualitative traits assessed. In conclusion, O. communa did not increase the amount or allergenicity of ragweed pollen grains in our experimental conditions.

Direct effects of insecticides on common ragweed-implications for natural enemy exclusion trials

Experimentally applying pesticides is an important method to assess the efficacy of weed biocontrol agents, but potential direct effects of the chemicals on plant performance are controversial or unknown. We assessed how three broad-spectrum insecticides applied in combination affect the performance of the widely invasive, crop-yield reducing, allergenic common ragweed (Ambrosia artemisiifolia L.) in an insect-free environment. Spraying insecticides had no significant effects on aboveground dry weight, seed and pollen output or pollen allergenicity, and only explained 1-8% of variation in these parameters. Our insecticide treatment can hence be applied to assess biocontrol impact on biomass and reproductive output of common ragweed. As our insecticide treatment delayed senescence, however, other methods of insect exclusion should be preferred when studying common ragweed phenology.