The gall miteAceria cladophthirus. I. Life-cycle, survival outside the gall and symptoms' expression on susceptible or resistantSolanum dulcamara plants

Abstract

The gall miteAceria cladophthirus (Nalepa) is able to survice outside its gall on detached leaves ofSolanum dulcamara L. kept under non-aseptic in-vitro conditions. The survival rate of the females on susceptible leaves is about 90% after 1 day and 85% for the following days. In contrast, on resistant leaves, less than 40$ survive after 1 day while necrotic local lesions develop and later the mortality increases severely. However, the mite only completes its life-cycle on susceptible leaves. The life-cycle forA. cladophthirus takes about 12 days: six days for egg incubation and six days for two instars growth. Its life-history is simple, without alternating females specialised for hibernation; arrhenotokous parthenogenesis occurs in experimental conditions. Eggs do not play any role in gall formation. Immature stages induce gall symptoms but are less efficient than females. Mite feeding only induces complete gall symptoms on the less differentiated leaves of susceptible shoots. On susceptible detached leaves, gall symptoms are similar but weaker and their intensity decreases with increasing leaf age; fully expanded leaves remain free of symptoms.

On resistant plants, mite feeding induces a hypersensitive response: necrotic local lesions, about 350 μm in diameter, appear both on shoots and on detached leaves. However, young leaves develop smaller lesions than old ones. Females induce larger lesions than first larvae. Once necrosis formation is initiated, it proceeds to completion regardless of the duration of mite feeding.