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An ecological study of the damage done to avocado fruits by citrus leafhopper Penthimiola bella (Cicadellidae) and coconut bug Pseudotheraptus wayi (Coreidae) in South Africa

by Dupont, F.M.A; Dennill, G.B.
Publisher: Abr-Jun 1996ISSN: 0967-0874.Subject(s): PERSEA AMERICANA | PENTHIMIOLA BELLA | PSEUDOTHERAPTUS WAYI | PLAGAS DE PLANTAS | MORBOSIDAD | DAÑOS | SUDAFRICA | PERSEA AMERICANA | PESTS OF PLANTS | MORBIDITY | DAMAGE | SOUTH AFRICA | PERSEA AMERICANA | RAVAGEUR DES PLANTES | MORBIDITE | DEGAT | AFRIQUE DU SUDOnline Resources: Es In: International Journal of Pest Management (RU) v. 42(2) p. 107-112Summary: Many biologists perceive organisms as constantly evolving and therefore consider the host plant ranges of biological control agents as labile. Host plant ranges are thus likely to undergo adaptive change should environmental conditions change, for example following successful biological control. As a consequence, the introduction of biological control agents against weeds is considered by many to be an inherently unsafe practice with non-target plants at risk of attack. However, despite the introduction of over 600 insect species from one geographic region to another for biological weed control during this century, there are relatively few documented cases of changes in host plant range. Purported instances are discussed in relation to behavioural and genetic concepts. It is concluded that apparent additions to the host range can, in all of the cases examined, be explained in terms of established behavioural concepts of preadaption, threshold change resulting from host deprivation, and effects of experience (learning). The inappropriateness of the oftenused term 'host shift' to describe these cases is demonstrated, and it is concluded that evidence from biological weed control contradicts some aspects of ecological and evolutionary theory.
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Many biologists perceive organisms as constantly evolving and therefore consider the host plant ranges of biological control agents as labile. Host plant ranges are thus likely to undergo adaptive change should environmental conditions change, for example following successful biological control. As a consequence, the introduction of biological control agents against weeds is considered by many to be an inherently unsafe practice with non-target plants at risk of attack. However, despite the introduction of over 600 insect species from one geographic region to another for biological weed control during this century, there are relatively few documented cases of changes in host plant range. Purported instances are discussed in relation to behavioural and genetic concepts. It is concluded that apparent additions to the host range can, in all of the cases examined, be explained in terms of established behavioural concepts of preadaption, threshold change resulting from host deprivation, and effects of experience (learning). The inappropriateness of the oftenused term 'host shift' to describe these cases is demonstrated, and it is concluded that evidence from biological weed control contradicts some aspects of ecological and evolutionary theory.

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