ENGLISH VERSION

ZESZYT 381

Interactions between host plants and Coccus hesperidum L. (Hemiptera; Sternorrhyncha; Coccidae) 
zeszyt 381, ss. 122

Understanding of complex relationships between the insects and their hosts is one of the main aims of current ecology and plant protection. Although a great number of Sternorrhyncha studies have been carried out on basic plant–insects interactions during the last ten years, interaction between plants and scale insects are poorly described. Therefore the following research aims were accepted in order to determine: 1) the effect of host plants on morphometric, demographic parameters and age structure of C. hesperidum developing on various host species; 2) the plant acceptance and colonization by C. hesperidum 3) the process of C. hesperidum feeding monitored in plant tissues using EPG; 4) honeydew excretion dynamics on various host plant species; 5) the response of C. hesperidum to host plant biochemical properties; 6) the effect C. hesperidumfeeding on biochemical changes of colonized plants; 7) host plant susceptibility to C. hesperidum feeding.

The studied material consisted of two-year old plants of Citrus limon var. Ponderosa, Ficus benjamina and Nephrolepis biserrata. For artificial colonization Coccus hesperidum a polyphagous pest of ornamental plants was selected. Identification of particular stages of C. hesperidum was conducted based on microscopic sliders. The feeding behaviour of soft brown scale was monitored using the technique of EPG [Leszczyński and Tjallingii 1994]. The analysis of C. hesperidum honeydew excretion activity was performed following the method by Koteja [1981] modified by Golan [2008a]. The biochemical and physiological analysis of plants material control and infested by scale insects was performed using commonly known methods described in literature.

The study demonstrated significant differences between the time of pre-reproductive period and females average daily fecundity only for C. hesperidumfeeding on lemon and ficus and over 98% mortality of the first-instar nymphs from F. benjamina. During presented study C. limon var. Ponderosa was the most abundantly colonized host species. However in the free-choice test nearly 50% of mobile instar nymphs of C. hesperidum chosen F. benjamina for a suitable host for feeding on. The results of EPG tests proved that females feeding on C. limon var. Ponderosa and N. biserrata faster started plant tissues penetration, shorter penetrated peripheral tissues and longer ingested phloem sap compared to individuals from F. benjamina. The values of honeydew excretion rate and daily excretion of C. hesperidum decreased with insect’s age. The leaves of analyzed host plantsdiffered significantly in the content of primary and secondary metabolites. F. benjamina leaves contained highest amount of sugars and protein nitrogen but the highest content of essential and non-essential amino acids was characteristic for the control leaves of N. biserrata. Among analyzed host plants the highest content of tannins was noted in lemon leaves, when leaves of ficus were characterized by significantly highest content of flavonoids and leaves of fern – phenolic acids. Scale insects infestation caused increase concentration of sugars and usually decrease in other examined primary metabolites concentration in leaves. Also the changes in physiological state of the plants are a result of C. hesperidum feeding, changes depend on host plant species and number of individuals feeding on it. Constant high activity of antioxidative enzymes and malondialdehyde level is characteristic for F. benjamina which is the least susceptible on soft brown scale feeding. The analyzed parameters changes in the leaves of lemon and fern were the strongest during C. hesperidum individuals feeding on the leaves in density class II and V. The threat for resistance mechanisms breaking in these plants is soft brown scale population in a number from 11 to 30 individuals per 1 leaf, for which maximum level of the analyzed physiological parameters is observed. In C. limonvar. Ponderosa, plants colonization with this number of insects caused the changes in cell membranes permeability leading to their degeneration and plants leaves dying.

The examined plant species are characterized by various degree of susceptibility on C. hesperidum feeding. Low degree is characteristic for Ficus benjamina, on which a decreased rate in a development of C. hesperidum colonies was noted with unprofitable influence of this plant on morphometric, demographic parameters, as well as feeding and honeydew of this scale insect. The studies for the first time have shown the differences in the degree of plants acceptance by C. hesperidum are conditioned by their constitutional properties: leaves structure and mainly biochemical composition. The differences in host plants colonization by scale insects result from an induction via stimulation or limitation of the concentration of substances constitutionally observed in the plants. The results obtained may be used in the practice, and especially practical application may be found for the results of the study on honeydew process and on mechanisms of plants resistance on C. hesperidum feeding.