Wj. Dekogel et al., VARIATION IN PERFORMANCE OF WESTERN FLOWER THRIPS POPULATIONS ON SUSCEPTIBLE AND PARTIALLY RESISTANT CUCUMBER, Entomologia experimentalis et applicata, 83(1), 1997, pp. 73-80
Biotypic variation is of major concern in breeding for host plant resi
stance to insects. The existence or development of aggressive biotypes
can lead to a rapid break-down of host plant resistance. Therefore th
e study of biotypic variation should be included in breeding programs
for resistance to insects. In the present study we measured the reprod
uction of randomly collected females of ten different populations of t
he insect herbivore Frankliniella occidentalis (Pergande) (Thysanopter
a: Thripidae) on one susceptible and two resistant cucumber (Cucumis s
ativus L.) accessions. Significant differences between thrips populati
ons were observed on all three cucumber accessions. None of the popula
tions had a significantly higher reproduction than the Dutch reference
population NL1. For three populations, the Dutch population NL1, a po
pulation from New Zealand (NZ), and an Italian population (IT), partia
l life history parameters, such as reproduction rate, developmental ti
me and survival were determined and the relative rate of increase r(r)
was calculated. On all three cucumber accessions the r(r)-value of po
pulation NZ was lower than of populations NL1 and IT. It is concluded
that there is biotypic variation in F. occidentalis with regard to per
formance on cucumber plants with different levels of resistance. Repro
duction is a good criterion for differentiating biotypes of F. occiden
talis on cucumber.