Habitat of the corn leafhopper (Hemiptera: Cicadellidae) during the dry (winter) season in Mexico

Although the corn leafhopper Dalbulus maidis (DeLong and Wolcott) is the most important vector of maize pathogens in Latin America, little is known about how and where it overwinters (passes the dry season), particularly in Mexico. The objectives of this study were (1) to monitor the abundance of D. maidis adults throughout the dry season in maize and maize-free habitats and (2) to determine where and how D. maidis adults, exposed or nonexposed to the maize pathogen Spiroplasma kunkelii Whitcomb, overwinter in a maize-free habitat. Work for the first objective was done during the two consecutive dry seasons of 1999-2000 and 2000-2001; the second objective was done during the dry seasons of 2003-2004 and 2005-2006. During the dry winter seasons, D. maidis was prevalent as long as maize was present in irrigated areas. The leafhopper was found in 52 of the 58 irrigated maize fields sampled in Mexico at the end of the dry seasons of 1999-2000 and 2000-2001. However, leafhopper adults were not found in nonirrigated maize-free habitats at high elevation during the dry winter season (February, March, and April), although leafhopper adults were prevalent on perennial wild grasses in January after maize harvest. Additional experiments revealed, however, that corn leafhopper adults, although few in number, survived the entire dry season in these nonirrigated maize-free fields. Also, no detectable difference in survival existed between leafhoppers exposed and those not exposed to S. kunkelli during the two dry seasons in the maize-free habitat. © 2007 Entomological Society of America

Movement of Cicadulina storeyi [Homoptera:Cicadellidae] in maize fields and its behavior in relation to maize growth stage

The movement of Cicadulina storeyi China (Homoptera: Cicadellidae), vector of maize streak geminivirus, within maize (Zea mays L.) fields was studied using mark, release and recapture experiments. Cicadulina storeyi, marked with fluorescent dye, were released at dusk and monitored for 14 days using yellow sticky traps placed at different distances (5–160 m) and directions from the release point. The suitability of maize growth stage for settling by C. storeyi was also investigated. Catches decreased steadily with distance from the release point and exponentially with time following the release. The mean leafhopper dispersal rate varied between 2.6 and 2.8 m/day for dry season and rainy season tests, respectively. The dispersal rate increased with distance from 1.4 m/day at 5 m to 13.6 m/day at 160 m. Wind was a major factor affecting direction of leafhopper movement with the largest proportion of C. storeyi collected downwind. Investigations on the suitability of maize growth stage for settling by C. storeyi revealed that the leafhopper preferred young plants (2–6 weeks after planting) to old one

Endophytic fungi decrease available resources for the aphid Rhopalosiphum padi and impair their ability to induce defences against predators

1. The production of winged morphs is a well known mechanism of induced defence in aphids to escape from natural enemies, and is also a reaction to poor resource quality. 2. Host plants of aphids often associate with endophytic fungi that have been shown to reduce the fitness of some species of aphids. 3. It was hypothesised that endophyte infection of host plants that represent a low quality plant resource should increase the aphid’s induced response to a predator because both low plant quality and predator presence represent a stronger cue for wing production than predator presence alone. 4. In a laboratory experiment, bird cherry-oat aphids Rhopalosiphum padi L. were exposed to the factors predator threat and endophyte infection and the effects of these factors on the proportion of winged morphs produced by the aphid colonies was analysed. 5. The presence of endophytic fungi strongly decreased aphid colony sizes. When a predator threat was present, all colonies on endophyte-free grasses produced winged morphs whereas only a few colonies were able to produce winged morphs on endophyteinfected grasses. However, these few colonies produced larger proportions of winged morphs than colonies on endophyte-free grasses. Without a predator threat, no colonies on endophyte-infected grasses produced any winged morphs. 6. These results show that aphids in stressed conditions and with reduced fitness will only invest in inducible defences when predators are present but are unable to produce winged morphs in response to endophyte presence

Haloperidol, dynamics of choice, and the parameters of the matching law

Although the corn leafhopper Dalbulus maidis (DeLong and Wolcott) is the most important vector of maize pathogens in Latin America, little is known about how and where it overwinters (passes the dry season), particularly in Mexico. The objectives of this study were (1) to monitor the abundance of D. maidis adults throughout the dry season in maize and maize-free habitats and (2) to determine where and how D. maidis adults, exposed or nonexposed to the maize pathogen Spiroplasma kunkelii Whitcomb, overwinter in a maize-free habitat. Work for the first objective was done during the two consecutive dry seasons of 1999-2000 and 2000-2001; the second objective was done during the dry seasons of 2003-2004 and 2005-2006. During the dry winter seasons, D. maidis was prevalent as long as maize was present in irrigated areas. The leafhopper was found in 52 of the 58 irrigated maize fields sampled in Mexico at the end of the dry seasons of 1999-2000 and 2000-2001. However, leafhopper adults were not found in nonirrigated maize-free habitats at high elevation during the dry winter season (February, March, and April), although leafhopper adults were prevalent on perennial wild grasses in January after maize harvest. Additional experiments revealed, however, that corn leafhopper adults, although few in number, survived the entire dry season in these nonirrigated maize-free fields. Also, no detectable difference in survival existed between leafhoppers exposed and those not exposed to S. kunkelli during the two dry seasons in the maize-free habitat. " 2007 Entomological Society of America.",,,,,,"10.1603/0046-225X(2007)36[1066:HOTCLH]2.0.CO;2",,,"http://hdl.handle.net/20.500.12104/41828","http://www.scopus.com/inward/record.url?eid=2-s2.0-35748967911&partnerID=40&md5=3ca64ced028c9f7603cdce76f76d46c