Intercrop Relationships and Spider Mite Dispersal in a Corn/Peanut Agro‐ecosystem

Abstract

Crawling was determined to be an important dispersal mechanism for spider mites leaving border vegetation and entering corn fields early in the season. This dispersal did not appear important in peanut fields. Large populations of spider mites in field corn were found responsible for subsequent infestations in peanuts. As corn plants senesced, mites began crawling to the periphery of the corn plant and grouping in masses on leaf tips, tassels and silks. During this period of mite movement, large numbers of mites were dispersed from the corn on wind currents and carried to nearby host plants. Aerial trapping verified this dispersal of mites and their subsequent colonization of previously uninfested peanut fields. Mites labelled in corn with a fluorescent powder were later found on peanut plants confirming the interhost movement. RÉSUMÉ Dispersion des tétranyches et relations entre champs voisins de maïs et d'arachide Dans le S. E. des U.S.A. Tetranychus urticae Koch est un ennemi sévère de nombreuses cultures. Il attaque souvent le mais le N. E. de la Caroline du Nord en juin et juillet: cependant les pullulations sur arachide se produisent généralement en aoǔt et septembre. Les tétranyches peuplent la végétation sauvage sur les bords des champs chaque printemps, quelle que soit la nature de la culture. Ces acariens pénètrent dans le champ à partir de cette végétation limitrophe et commencent à consommer le maïs. Les dégǎts sont plus sévères le long des bords. A cette époque, pour des raisons inconnues, très peu d'acariens ont émigré dans les champs d'arachide. Quand les acariens attaquent les arachides (aoǔt — septembre), il y a rarement cet effet de bordure. L'absence d'effet de bordure est dǔ au fai que les acariens se déplacent dans la culture d'arachide de différentes façons. L'éloignement des acariens de la plante a été observé quand le maïs se dessèche en juillet. Pendant ce déplacement, de nombreux acariens sont dispersés par le vent. La capture de tétranyches sur des lames de microscope engluées suspendues au‐dessus du maïs et des arachides, confirme cette dispersion aérienne. Ces acariens abandonnent un hǒté dépérissant (le maïs) pour coloniser les champs antérieurement sains d'arachide. L'utilisation de poudre fluorescente pour marquer les acariens sur le maïs permet de les récupérer sur les champs adjacents d'arachide, ce qui confirme le changement d'hǒtes. 86% des acariens capturés sur les lames engluées sont des femelles; ceci montre l'utilisation maximale du comportement de dispersion pour libérer les éléments reproducteurs.

Responses to direct and indirect selection on aerial dispersal behaviour in Tetranychus urticae

“…They can land on plants in surround-ing areas or at a distance of several kilometres (Brandenburg & Kennedy, 1982). Although mites in all life stages, except adult males, can display aerial dispersal behaviour when food is denied and both light and wind are present (Smitley & Kennedy, 1985), young adult females (1-2 days old) are the predominant dispersers (Li & Margolies, 1993a).…”

“…greenhouse, field crop) ecosystems (Kennedy & Margolies,I 985a,b). Mites can achieve long distance dispersal as aerial plankton on wind currents (Brandenburg & Kennedy, 1982;Hoy et at., 1984). Aerial dispersal in tetranychid mites does not occur primarily by chance but is the result of an active behaviour that enhances the probability of mites being carried aloft from plant surfaces (Smitley & Kennedy, 1985;Margolies, 1987).…”

Genetic diversity of the cotton aphid Aphis gossypii in the unstable environment of a cotton growing area

“…Insect pest population dynamics in an agricultural landscape is dictated by the ability of the insects to disperse to and to exploit different habitat patches. Populations may move over great distances ( Stinner et al , 1983;Loxdale & Lushai, 1999 ), whereas others may move more locally by tracking a sequence of temporarily suitable host plants ( Brandenburg & Kennedy, 1982;Shelton & North, 1986 ). Consequently, many polyphagous pests exploit a sequence of crops that offer a substantial but time limited resource, and uncultivated or scarce hosts that permit them to bridge the critical period.…”

Dinâmica da resistência de Brevipalpus phoenicis (Geijskes, 1939) (Acari: Tenuipalpidae) ao acaricida dicofol.

“…Este mecanismo de dispersão pode exercer influência significativa na infestação inicial das culturas. Trabalho realizado por Brandenburg & Kennedy (1982) Hoy et al (1984) descreveram que na ausência de alimento estes ácaros apresentam o comportamento de distender as pernas anteriores e posicionar o corpo na vertical e apoiados pelas pernas posteriores quando submetidos a correntes fracas e moderadas de vento.…”

“…Trabalhos realizados com Tetranychus urticae (Koch) mostraram a importância da dispersão por caminhamento na infestação inicial de plantações de milho, sendo que os ácaros eram provenientes de plantas hospedeiras próximas e dentro destas plantações (Brandenburg & Kennedy, 1982;Kennedy & Smitley, 1985). Trabalhos realizados por…”