Modern Maize Hybrids Have Lost Volatile Bottom-Up and Top-Down Control of Dalbulus maidis, a Specialist Herbivore

Following damage by herbivores, many plants release volatiles that dissuade future conspecifics from feeding. In many crop plants however, induced volatiles mediating this kind of interactions among plants, herbivores and also their natural enemies have been altered through the process of domestication. The selection of crops for increased yield may have gone at a cost of defense, possibly including defense-related volatiles. Dalbulus maidis (Hemiptera: Cicadellidae), a specialist leafhopper that only feeds on Zea spp., is a vector of Corn Stunt Spiroplasma, a serious maize disease. Here, we compared the volatiles released following D. maidis attack by a maize landrace and two maize hybrids of temperate and tropical background. Also, we performed behavioral assays with the leafhopper contrasting healthy non-attacked maize seedlings versus attacked seedlings. The maize landrace produced more than 6-fold larger quantities of induced volatiles compared to the maize hybrids after herbivory. Corn leafhopper females were able to detect and significantly preferred the odors of healthy seedlings over the attacked ones only in the landrace. They did not discriminate between the attacked and non-attacked hybrids. Additionally, we found that the attraction of the parasitoid wasp Anagrus virlai (Hymenoptera: Mymaridae) to its host was diminished in the tested hybrids. The parasitoid was able to detect the odors of the attacked landrace, however it was unable to discriminate between healthy and attacked maize hybrid plants. These results suggest that those more domesticated germplasms may have lost the ability not only to release volatiles that avoid colonization of future herbivores, but also to attract their natural enemies in a tritrophic system.

n., an Egg Parasitoid of the Corn Leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) in the New World, and Anagrus incarnatus from the Palaearctic Region (Hymenoptera: Mymaridae)

The common New World egg parasitoid of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), an economically important pest of maize from Argentina to southern USA, has long been misidentified as the Palaearctic species Anagrus incarnatus Haliday or its synonym A. breviphragma Soyka (Hymenoptera: Mymaridae). Using a combination of genetic and morphometric methods, and available biological information, specimens reared from eggs of D. maidis in Argentina and Mexico, described and illustrated here as Anagrus (Anagrus) virlai Triapitsyn sp. n., are shown to be different from those of A. incarnatus from the Palaearctic region. Mitochondrial and nuclear ribosomal DNA sequence data provide clear evidence for the separation of the two species. Anagrus virlai is also known from Brazil, Colombia, Guadeloupe (France), and Guyana.

Long-distance dispersal by a parasitoid (Anagrus delicatus, Mymaridae) and its host

We demonstrate that an egg parasitoid, Anagrus delicatus (Mymaridae, Hymenoptera) and its host, Prokelesia marginata (Delphacidae, Homoptera) regularly disperse 1 km or more in a north Florida saltmarsh. Anagrus delicatus were caught on yellow sticky traps on offshore islets and oyster bars throughout the spring, summer, and fall, whereas P. marginata were caught during one pulse in the spring. Parasitism rates were higher on offshore islets than at mainland sites, even though egg densities were higher at the mainland sites. The majority of parasitoids caught offshore were females. Long-distance dispersal by A. delicatus may be a cause of inverse density-dependent or density-independent spatial patterns of parasitism and may represent a risk-spreading strategy.