Abstract
The gall wasp,Trichilogaster sp., was imported from Australia to assess its potential as an agent for the control of the invasive shrub/treeAcacia pycnantha Benth. in South Africa. Host specificity tests indicate safety for release; of 19 tree/shrub species tested, including 16 species closely related toA. pycnantha, galls developed only onA. pycnantha. However, galling intensity remained consistently low on the host plant; only 21–29% of the branches exposed to the wasp were galled during 3 years of rearing. Neither the prolonged presence of males in test cages (someTrichilogaster species are thelytokous) nor the stage of maturity of reproductive buds exposed to oviposition affected the percentage of branches galled. It is not recommended thatTrichilogaster sp. be released before the possibility of insect-plant homeostasis or mis-matching of wasp and host plant populations/strains/subspecies is investigated, especially since galling intensities of 30% were ineffective in reducing seed production of a relatedTrichilogaster species/Acacia association.
Résumé
Le cynips,Trichilogaster sp., a été introduit d'Australie afin d'évaluer ses aptitudes en tant qu'agent de lutte en Afrique du Sud contre l'arbuste/arbre envahissantAcacia pycnantha Benth. Des essais de spécificité vis-à-vis de l'hôte ont permis d'établir que l'emploi de l'insecte est sans danger: en présence de 19 espèces d'arbustes/arbres (dont 16 espèces étroitement apparentées), l'hyménoptère n'a formé de galles que surA. pycnantha. Cependant, la formation de galles sur la plante hôte est demeurée de faible amplitude: sur 3 ans d'élevage, uniquement 21 à 29% des branches ont été atteintes. Le pourcentage de branches atteintes n'a été influencé ni par la présence prolongée des mâles dans les enceintes d'essai (certaines ▪▪ deTrichilogaster spp. sont parthénogénétiques), ni par le stade de croissance des bourgeons reproductifs exposés à l'oviposition. L'emploi deTrichilogaster sp. est déconseillé avant que la possibilité d'homéostasie entre plante et insecte, d'association erronée entre les populations/souches/sous-espèces de plantes hôtes et l'insecte ait été examinée, d'autant plus que des pourcentages de formation de galles de 30% se sont avérés inefficaces lors d'une association du même genre entreTrichilogaster spp. etAcacia.
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Dennill, G.B., Gordon, A.J. Trichilogaster sp. [Hymenoptera: Pteromalidae], a potential biocontrol agent for the weedAcacia pycnantha [Fabaceae] . Entomophaga 36, 295–301 (1991). https://doi.org/10.1007/BF02374565
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DOI: https://doi.org/10.1007/BF02374565