Population dynamics of nematode transmission in western flower thrips on caged impatiens

To evaluate potential of Thripinema nicklewoodi (Tylenchida: Allantonematidae) as a biological control agent of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), dynamics of nematode transmission were studied in two experimental thrips populations with different initial parasitism rates in caged impatiens plants. The initial parasitism rates of adult female thrips were set at 50% in a ‘Low nematode’ treatment and at 70% in a ‘High nematode’ treatment and were compared to a control population. Transmission of T. nicklewoodi persisted for seven host generations in both nematode treatments. There was convergence in both number of parasitized thrips and percent parasitism among all the subpopulations of the western flower thrips, and no differences were found between the two treatments. The highest parasitism rates were in adult female thrips, reaching 52% in the second generation of the ‘Low nematode’ treatment and 48% in the fifth generation of ‘High nematode’ treatment. Populations of healthy (i.e., not parasitized) female thrips declined 50–79% in the ‘Low nematode’ treatment and 39–73% in ‘High nematode’ treatment compared to the control thrips population between the fourth and seventh generations. However, no significant reductions were found in numbers of larval thrips in either treatment, compared to controls, and the numbers of larval thrips were not different between the two treatments. Higher proportion of male in thrips populations with nematode was observed during the last four sampling dates when adult female thrips declined significantly in both treatments compared to control population.