Entrapment of two-spotted spider mite, Tetranychus urticae (Acari: Prostigmata: Tetranychidae), by type IV glandular trichomes of Lycopersicon species

Two-spotted spider mite (TSSM) is becoming resistant to many of the pesticides used in the tomato
fields. A potential alternative method of control is host plant resistance, which may be mediated by
glandular trichomes. In this experiment, level of entrapment and mortality of the pest by type IV
glandular trichomes were studied on accessions of Lycopersicon hirsutum Humb & Bonpl, L. pennellii
(Cor.) D’Arcy and L. esculentum Mill on leaflets with trichomes intact or with exudates removed. Three
accessions of L. hirsutum (LA1740, LA1777 and LA2860), two accessions of L. pennellii (LA2963 and
LA2580) and one susceptible variety (Sankranthi) of L. esculentum were used. Leaflets from the terminal
pair of the third-last fully expanded leaves were excised and leaf disks prepared. Ten female mites of
Tetranychus orticae Koch were placed on the adaxial leaflet surface of each disk and after 2 h, the
number of mites trapped, untrapped and moved into water were recorded. Again after 24 and 48 h, mites
were recorded either dead, morbid or moved into water. Results indicated that the highest number of
entrapment was on L. hirsutum LA1777, followed by L. pennellii accessions. None of the mites was
entrapped on L. esculentum. Moreover, L. hirsutum (LA1777 and LA1740) and L. pennellii accessions
had greater number of dead mites than L. esculentum after 48 h. Lycopersicon esculentum did not possess
type IV glandular trichomes. The highest density of type IV glandular trichomes was recorded on abaxial
and adaxial leaf surfaces of L. hirsutum LA1777 (86.72 and 34.44 trichomes/mm², respectively). Removal
of trichome exudates has significantly increased the mite survival in resistant accessions. Correlation
between the density of type IV glandular trichomes and entrapment rate of TSSM was significantly
positive.