Biology, ecology and management of white wax scale, Ceroplastes destructor Newstead (Hemiptera: Coccidae), on citrus and syzygium

[摘要] ENGLISH ABSTRACT:The population density of the white wax scale, Ceroplastes destructor Newstead, hasincreased since 1994 in certain areas of Western and parts of Eastern Cape Provinces ofSouth Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A studywas conducted to investigate its morphology, biology and ecology as contributions to thedevelopment of a sound integrated management programme.Characteristics of the immature stages and adult females were described andillustrated from field-collected and slide-mounted specimens. A key to the differentstages and morphometeric characteristics useful for separating them are provided. Nosignificant differences in female fecundity were found between orchards (P > 0.05).However, fecundity varied significantly between female size classes from the sameorchard (P < 0.001). Female body-size also differed significantly between orchards (P <0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructorhas one discrete generation per year in South Africa. Oviposition commenced inNovember and continued through to the end of December with a few females ovipositinguntil mid January. Population density of the second instar peaked in February while thethird instar extended from March to the end of July, followed by a peak population ofadults in August. Seven primary and three secondary parasitoids, as well as four predatorspecies attacking C. destructor were identified. Aprostocetus (= Tetrastichus)ceroplastae (Girault) was the dominant species, accounting for 78.87% of the totalprimary parasitoids reared. Peak numbers of parasitoids and predators were synchronizedwith peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Keymortality factors varied slightly between two of the orchards. Key stage mortalitydetermined from a cohort life table was generally in the third instar (LIlI) and preovipositionalfemale (POF) stage. Significant density-dependent mortality factors weredemonstrated for the first instar (LI) and PDF stage.Dispersal of C. destructor is by first instar nymphs and the numbers caught on aseries of yellow sticky traps varied significantly between crawler densities at the source,trap distances and trap directions from the source (P < 0.001). The numbers caught werepositively correlated to the initial crawler density at the source (P < 0.01), suggesting thatdispersal was density dependent. Trap distance and the numbers caught were inverselycorrelated (P < 0.01). Evaluation of effects of different densities of C. destructor ongrowth, survivorship and reproduction of scales as well as on leaf bearing ability of treesand area of leaf surface covered with sooty mould fungus was carried out on naturallyinfested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecunditywere inversely related to scale density (P < 0.01), suggesting density-dependentintraspecific competition. Scale survivorship generally declined with increasing densitywhereas scale parasitism and predation were positively correlated with density (P < 0.05).At high scale densities production of new leaves was significantly reduced (P < 0.01),reducing the resource base for subsequent generations of scale. Scale density and leafarea covered with sooty mould fungus were significantly positively correlated (P < 0.05).The toxicity of four synthetic insecticides against the three immature stages of C.destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated.Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatmentsapplied at the LIII stage were not significantly affected by any of the chemicals (P >0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are notrecommended for integrated management of C. destructor in citrus orchards where A.ceroplastae plays an important role.

[发布机构] Stellenbosch University