Biology and ecology of Eucalyptus psyllid pests in South Africa

Abstract

As with other invasive insect pests, eucalypt-feeding psyllids can cause significant economic loss of eucalypts globally. Currently, the Eucalyptus plantations in South Africa are hosts to a number of eucalypt-feeding psyllids, namely Spondyliaspis cf. plicatuloides (Froggatt), Glycaspis brimblecombei Moore, Ctenarytaina eucalypti (Maskell) and Blastopsylla occidentalis Taylor. To better understand the threat of eucalypt-feeding psyllids to this industry globally, a comprehensive review of their diversity, distribution, biology and impact was compiled. Beside their high diversity in Australia, the review points out how little we know about psyllids reported as invasive for the first time, such as S. cf. plicatuloides, a recent introduction in South Africa. To manage eucalypt-feeding psyllids, long-term strategies, including resistant genotypes and parasitoids are required, which also requires a thorough understanding of their biology and seasonality. In a first part of this study, the biology of S. cf. plicatuloides was studied under controlled conditions using Corymbia ficifolia as the host. Females reached reproductive maturity two days after eclosion and on average laid 16 eggs/female. The first nymphal instars took approximately 11 days to hatch from the eggs. Five nymphal instars completed their development in about 23 days under the lerps. The insect’s total life cycle lasted approximately 37 days. Male and female longevity averaged about four and six days respectively. Factors influencing host preferences of S. cf. plicatuloides and G. brimblecombei are also unknown. For this reason, potential morphological and phytochemical leafy features were assessed in six preferred and six non-preferred eucalypt species in a second research chapter of the study. None of the morphological features were related to host preferences. GC/MS determined the composition of essential oils and polar metabolites in and on the surface of leaves. The abundance of certain terpenes, diterpenes, triterpenes, phenylpropanoids, organic and fatty acids was related to host preferences. Results suggest that leafy phytochemistry, rather than leafy morphology, influences host preference for both psyllids. A third part of the study assessed host specificity and host stage preference of three psyllid parasitoids namely Psyllaephagus blastopsyllae, P. pilosus, and P. bliteus, choice and no choice experiments towards the four invasive psyllids were evaluated. Results revealed that two Psyllaephagus spp. are not host specific, whereas one was highly host specific. Furthermore, all the tested parasitoids preferred third and fourth nymphal instars for oviposition. In a final part of this study, seasonal occurrence of S. cf. plicatuloides in South Africa was initiated, which covered all the life stages in three distinctive sites. Moreover, a first-time study to determine the seasonal occurrence of the adults of other invasive eucalypt-feeding psyllids namely B. occidentalis, C. eucalypti and G. brimblecombei was initiated. The initial results of these studies are presented, but additional data is needed to validate the pattern of psyllids’ seasonality. In conclusion, the current study provides foundational information on the biology, host preference, interactions with natural enemies, and seasonal occurrence of the newly reported psyllid, S. cf. plicatuloides, as well as other eucalypt-feeding psyllids in South Africa, which will inform knowledge-based management programs and future research.