The importance of alternative host plants as reservoirs of the cotton leaf hopper, Amrasca devastans, and its natural enemies

Many agricultural pests can be harboured by alternative host plants but these can also harbour the pests’ natural enemies. We evaluated the capacity of non-cotton plant species (both naturally growing and cultivated) to function as alternative hosts for the cotton leaf hopper Amrasca devastans (Homoptera: Ciccadellidae) and its natural enemies. Forty-eight species harboured A. devastans. Twenty-four species were true breeding hosts, bearing both nymphal and adult A. devastans, the rest were incidental hosts. The crop Ricinus communis and the vegetables Abelmoschus esculentus and Solanum melongena had the highest potential for harbouring A. devastans and carrying it over into the seedling cotton crop. Natural enemies found on true alternative host plants were spiders, predatory insects (Chrysoperla carnea, Coccinellids, Orius spp. and Geocoris spp.) and two species of egg parasitoids (Arescon enocki and Anagrus sp.). Predators were found on 23 species of alternative host plants, especially R. communis. Parasitoids emerged from one crop species (R. communis) and three vegetable species; with 39 % of A. devastans parasitised. We conclude that the presence of alternative host plants provides both advantages and disadvantages to the cotton agro-ecosystem because they are a source of both natural enemy and pest species. To reduce damage by A. devastans, we recommend that weeds that harbour the pest should be removed, that cotton cultivation with R. communis, A. esculentus, and S. melongena should be avoided, that pesticides should be applied sparingly to cultivate alternative host plants and that cotton crops should be sown earlier

Design rules for high mobility xanthene-based hole transport materials

Tunable and highly conductive hole transport materials are crucial for the performance of organic electronics applications such as organic light emitting diodes and perovskite solar cells. For commercial applications, these materials\u27 requirements include easy synthesis, high hole mobility, and highly tuned and compatible electronic energy levels. Here, we present a systematic study of a recently discovered, easy-to-synthesize class of spiro[fluorene-9,9′-xanthene]-based organic hole transport materials. Systematic side group functionalization allows us to control the HOMO energy and charge carrier mobility. Analysis of the bulk simulations enables us to derive design rules for mobility enhancement. We show that larger functional groups (e.g. methyl) decrease the conformational disorder due to steric effects and thus increase the hole mobility. Highly asymmetric or polar side groups (e.g. fluorine), however, increase the electrostatic disorder and thus reduce the hole mobility. These generally applicable design rules will help in the future to further optimize organic hole transport materials

BIOLOGY AND REARING OF <i>PARAPHLEPSIUS IRRORATUS</i> (HOMOPTERA: CICADELLIDAE), A VECTOR OF PEACH X-DISEASE

AbstractA method of rearing Paraphlepsius irroratus (Say) under artificial conditions was developed by using a leguminous plant species as the oviposition host and a gramineous species as the food plant for nymphs. Nymphs completed their development on all 10 gramineous species tested. Total time for completion of the 5 nymphal instars ranged from 31.8 to 59.2 days, depending on the plant species used. With the exception of Alopecurus pratensis, all monocotyledonous species tested were found to be suitable food plants for nymphs, allowing 50% or more of the insects to survive for 3 weeks or more. Only 5 dicotyledonous species supported a similar survival level of nymphs. Adult survival remained above the 50% level on Apium graveolans var. dulce, 6 members of the Leguminosae, and all members of Composite with the exception of Callistephus chinensis. Survival of adult leafhoppers on monocotyledons was relatively high after 1 week but considerable mortality followed longer confinement. Although nymphs emerged from eggs laid on a wide range of plant species, the numbers recorded on monocotyledons suggest that monocots are important as oviposition hosts for P. irroratus in nature.</jats:p

The Court of Beast and Bough: Contesting the Medieval English Forest in the Early Robin Hood Ballads

After King William created the New Forest in the twelfth century, the English monarchy sought to define the vert, both legally and ideologically, as a site in which the king’s rights were vigorously enforced. In the romance literature of England, the forest was treated as an exclusive chivalric testing ground, as the site of the aristocracy’s self-validation. The folk reaction against the privatization of this common space and its resources finds a strong literary articulation in the first Robin Hood ballads centuries later. The outlaw reclaims the forest by inhabiting it, appropriating the symbols of its governance, and establishing within it a court that is both legal and social, decked out in the trappings and traditions of romance chivalry and the forest administration. This thesis examines the ideological impulses behind Robin’s occupation of the forest, discussing their relationship to the legal and literary history of the English forest

Transmission of Clover Phyllody Virus by the Leafhopper, <i>Paraphlepsius irroratus</i> (Say)

AbstractClover phyllody virus was transmitted from ladino clover to ladino clover by Paraphlepsius irroratus (Say). The preinfective period of the insect following acquisition of the virus was between 21 and 28 days. Nineteen of 25 plants fed on by leafhoppers that had completed their preinfective period became infected.</jats:p

EFFECTIVENESS OF ANTIBIOTICS APPLIED AS POSTINOCULATION SPRAYS AGAINST CLOVER PHYLLODY AND ASTER YELLOWS

Oxytetracycline HCl, tetracycline HCl, and doxycycline HCl, applied as foliage sprays to aster (Callistephus chinensis Nees), caused maximum delays in clover phyllody expression at concentrations of 800 ppm. Maximum delays of celery-infecting aster yellows were obtained at 600 ppm with oxytetracycline and at 1,000 ppm, the highest concentration used, with tetracycline and doxycycline. In tests with noncelery-infecting aster yellows, oxytetracycline and tetracycline produced maximum delays at between 600 and 800 ppm, whereas doxycycline proved most effective at 1,000 ppm. Methacycline reached a maximum at 600 ppm but was considerably less effective than were the other three tetracyclines. HCl and amphoteric formulations of oxytetracycline were more effective in delaying clover phyllody symptoms than was the calcium formulation. The HCl formulation was most effective against celery-infecting aster yellows but was followed closely by the amphoteric and calcium formulations. None of the five nontetracycline antibiotics proved effective. Increasing spreader concentrations appeared to decrease the effectiveness of tetracycline HCl. </jats:p

ADDITIONAL HOST PLANTS OF CLOVER PHYLLODY IN CANADA

Symptoms were observed on 35 out of 74 plant species, in 15 families inoculated with clover phyllody by the aster leafhopper (Macrosteles fascifrons (Stal)). Symptomatology for some of the hosts is described and illustrated. There were differences in numbers of plants infected, length of time for symptom development, and numbers of insects surviving on the various species of plants, but these were not correlated. Although the clover phyllody agent was transmitted to asters from 17 of 19 infected plant species the number of leafhoppers that became inoculative varied considerably depending on the source plant species. </jats:p