The biology, ecology and integrated pest management of Ctenarytaina thysanura (Ferris & Klyver) (Homoptera:Psyllidae) on Boronia megastigma (Nees) in Tasmania

This study investigates the behaviour, population dynamics and integrated pest management of Ctenarytaina thysanura (Ferris and Klyver), a psyllid attacking Boronia megastigma (Nees), an essential oil crop in Tasmania, during the period 1986-1989. C. thysanura was studied extensively on boronia plants under glasshouse and field conditions and its life cycle and biology documented. Aspects of mating behaviour, ovipositional patterns on the host plant and the spatial distribution of C. thysanura eggs in relation to the position of the nodes of the host plant's terminal shoots are described. Field tests on attraction of adults to coloured sticky traps revealed a clear preference for yellow and least preference for white. Psyllid capture rates were directly related to the proportion of light reflected in the 440-480nm range. C. thysanura was identified as a major pest of boronia causing 41.7 per cent flower yield loss in commercial stands. It confined its attack to young, actively growing boronia shoots. Feeding damage to the host plant was cumulative and very much apparent as nymphs entered the 4th and 5th stages. Based on boronia oil market values and psyllid control costs for 1988 and 1989, the economic injury level for young and mature plants was eight and 20 C. thysanura 4th and 5th nymphs per terminal shoot respectively. The host-plant relationships of C. thysanura were studied in detail for 23 boronia cultivars. No antibiosis effect was detected for any cultivar but an ovipositional antixenosis was detected in cultivar HC27, whereas cultivars HC4 and HC142 were most preferred for oviposition. No cultivar was tolerant to C. thysanura attack. Measurement of terminal shoot hardness of the cultivars showed variations in relative hardness. C. thysanura laid more eggs on those cultivars with softer terminal · shoots (HC4 and HC142) and laid few eggs on harder terminal shoots (HC27). Detailed studies were made of the population dynamics of C. thysanura on boronia during 1986-1989 on 0.5 ha plots at five locations. C. thysanura completed three generations each year in Tasmania and overwintered in all stages. Life tables were prepared for C. thysanura populations at all study areas and Varley and Gradwell's key factor analysis used to determine that predators and parasitoids were key mortality factors by acting on late nymphal stages. Other factors such as quantity and quality of available food plant and oviposition sites, intraspecific competition, emigration, cultural practices including pruning of terminal shoots, and harvesting of boronia flowers also modified C. thysanura populations. The results of the population study suggested that the absence of key mortality factors through indiscriminate and ill timed applications of insecticides enabled C. thysanura populations to reach high densities at which levels they destroyed the plant habitat. An integrated pest management (1PM) programme was developed for C. thysanura using a low dosage of mevinphos insecticide applied as a stem spray rather than as a foliage spray at the peak of the C. thysanura late nymphal stage. The application of mevinphos stem spray conserved parasitoids, which were then pupating in the mummified nymphs, by minimizing contact effects while killing the active host on the boronia plant and this reduced host density to a level where the natural enemies could act effectively to bring psyllid populations to non damaging levels. As a result the number of insecticide applications was reduced from 10-12 pre study to 3 in the initial stage of 1PM programmes. Subsequent levels of parasitism removed the necessity to spray in 1989/90.