Effect of temperature on infection, development and reproduction of the parasitic nematode Thripinema nicklewoodi in Frankliniella occidentalis
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The parasitic nematode Thripinema nicklewoodi Siddiqi (Tylenchida: Allantonematidae) is currently under investigation for use in inoculative release strategies against western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) infesting greenhouse floricultural crops. The aim was to determine whether temperatures within greenhouses would permit the establishment of T. nicklewoodi. The abilities of T. nicklewoodi to infect, develop and reproduce in WFT were assessed under a range of constant and fluctuating temperatures in the laboratory. At constant temperatures, T. nicklewoodi infected WFT over the range of 1-30C, although the temperature-related infection profile followed an asymmetric distribution around an optimum 20C (80% infection). The lower and upper thresholds for T. nicklewoodi in vivo development and reproduction were higher than for infection, at 10C and 35C, respectively. Climate data recorded over 1999-2000 in a commercial greenhouse (Texas) revealed a temperature range of 15C to 31C from early March through mid June, when WFT were most abundant. While low (nighttime) greenhouse temperatures are conducive for T. nicklewoodi, upper daytime temperatures are close to the upper threshold for infection and may reduce reproductive output. However, fluctuating temperature bioassays in the laboratory demonstrated that T. nicklewoodi maintained separately at the upper threshold temperatures for infection (30C) and development (35C) readily infected and developed in WFT when they were allowed intermittent (10 h daily) exposure to a permissive temperature in the range 10-20C. Drawing on the results, the diurnal temperature-fluctuations of various greenhouses growing ornamentals would permit the establishment of T. nicklewoodi.
