Identification and phenology of Hyalesthes obsoletus (Hemiptera: Auchenorrhyncha: Cixiidae) nymphal instars

Urtica dioica and Convolvulus arvensis are the main host plants of Hyalesthes obsoletus and play an important role in the epidemiology of Bois noir of grapevines. The earliest survey, which was carried out to compare the phenology of nymphal instars on U. dioica and C. arvensis, had highlighted some problems in the identification of the instars. Therefore, the correct identification of nymphs to species and instar level became a preliminary aim of this research. Adults and nymphs attributable to H. obsoletus were collected during 2008-2010 in three flatland vineyard habitats of northern Italy on U. dioica, C. arvensis and Artemisia verlotorum. Nymphs and morphologically identified adults of H. obsoletus were submitted to molecular identification. Morphometric and morphological studies were carried out on nymphs collected in the field or obtained in laboratory rearings. Molecular methods not only confirmed the identity of adults, but also allowed the assignment of the nymphs to this species. Morphometric and morphological characteristics (e.g. body and head-thoracic lengths, number of thoracic pits) showed the existence of five nymphal instars. Morphometric differences between newly hatched and older first-instar nymphs were observed. A key to distinguish the five instars was proposed. Evident differences between H. obsoletus nymphs studied here and elsewhere were identified. According to differences in adult-flight period, an earlier phenology of nymphs on C. arvensis than on U. dioica was observed. In particular, the typical overwintering instar was the second on U. dioica and the third on C. arvensis.

ISSR fingerprinting for the assessment of the bindweed biocontrol agent Stagonospora convolvuli LA39 after field release

AIMS

To develop a molecular identification method based on ISSR fingerprints to monitor the fungal leaf pathogen Stagonospora convolvuli LA39 used to biologically control bindweeds after a field release.

METHODS AND RESULTS

The developed method proved to be suitable to clearly distinguish LA39 from resident Stagonospora spp. and was applied in two field experiments. First, the environmental persistence of LA39 was assessed in an overwintering experiment. LA39 could be re-isolated from infected bindweed 1 year after field application, but with very low frequency of occurrence. Secondly, LA39 was applied in an area with natural bindweed infestation and re-isolated from infected bindweed. The dispersal of LA39 during one season was poor (4-5 m).

CONCLUSIONS

ISSR fingerprinting has been shown to be a valuable tool to monitor the environmental fate of S. convolvuli in the field. It is concluded that an LA39-based mycoherbicide will have minimal environmental impact caused by the restricted mobility, poor proliferation and poor persistence over seasons of LA39.

SIGNIFICANCE AND IMPACT OF THE STUDY

Studies about the dispersal and survival of biocontrol agents after field release as well as the development of methods needed for this purpose are indispensable for a comprehensive risk assessment for biocontrol agents.

Interactive Effects of Leaf Damage, Light Intensity and Support Availability on Chemical Defenses and Morphology of a Twining Vine

In a greenhouse study, we evaluated the effect of the light environment and support availability on the induction of tropane alkaloids (TAs) after leaf damage in the twining vine Convolvulus arvensis. We also tested whether leaf damage modifies the phenotypic responses of the plant to shade and physical support. We found a consistent pattern of induction of TAs after leaf damage in each environmental condition. The induction of TAs was differentially affected by combinations of support and light treatments. In the sun, prostrate and climbing vines exhibited similar induced responses. In the shade, prostrate vines showed greater induced responses. Thus, vines showed the greatest chemical induction when damage occurred in a resource-poor environment (shade), and there was no cue (support) of future increase in resource uptake. Damaged plants showed reduced plasticity to shading in leaf shape and internodes and petiole length in comparison with control, undamaged plants. Herbivory and/or induced responses to herbivory may limit adaptive plant responses to the environment. Therefore, the negative consequences of herbivory on plant fitness might be magnified in a context of changing environments.

Crop-weed competition between sunflower (Helianthus annuus L.) and Convolvulus arvensis L. in substitutive experiments

The main characteristics of a substitutive experiment is that the proportions of two species in the mixtures are varied while the overall density of the two species is maintained constant - a replacement series. In our experiments early competition between sunflower and field bindweed (Convolvulus arvensis) was studied in a replacement studies under glasshouse conditions. Pot experiments were set up with the following treatments: 1, sunflower 100% (6 plants pot(-1)); 2, sunflower 66.6% (4 plants pot(-1)) + C. arvensis 33.3% (2 plants pot(-1)); 3, sunflower 33.3% (2 plants pot(-1)) + C. arvensis 66.6% (4 plants pot(-1)); 4, C. arvensis 100% (6 plants pot(-1)). Sixty eight days after sowing dry weight of shoots and roots were measured and nitrogen (N), phosphorus (P) and potassium (K) content was also determined. Dry biomass production of sunflower was almost twice higher as compared to that of C. arvensis without interspecific competition. Dry weight of sunflower and C. arvensis shoots and roots for a plant continuously decreased by reducing their proportion in the mixtures. Higher biomass production of sunflower suggests, that its development is faster at the beginning of vegetation penod, therefore sunflower has better competitive ability in sunflower--C. arvensis mixtures in the early competition as compared to C. arvensis. Shoot:root ratio of plants did not change considerably in mixtures, but generally was ten times higher in sunflower plants, as compared to that of C. arvensis. Shoots generally contained macro elements at higher concentration as compared to those of roots. Total NPK content of sunflower was reduced by 53 and 82% for a pot, as its proportion decreased in the mixtures. More severe reduction in NPK content was observed in case of C. arvensis, which also proves stronger competitive ability of sunflower in the early vegetation.