Sampling for Estimating Frankliniella Species Flower Thrips and Orius Species Predators in Field Experiments

The western flower thrips is a major pest to vegetable, fruit and ornamental crops that will spread worldwide as a result of global trade. Efforts to control the pest with intended insecticide applications were unsuccessful creating problems with the development of insecticide resistance and associated outbreaks of secondary pests. The techniques are an efficient method to accurately quantify populations of the western flower thrips and other flower thrips species in field experiment.

The objectives are to determine the efficacy of management tactics including cultural tactics such as ultraviolet reflective mulch and conservation biological control programs using predatory minute pirate bugs. The techniques are critical in developing new management tactics against the western flower thrips and Other species of flower thrips are not even in other parts of the world. The techniques developed in Florida can be adapted to other geographical regions.

Demonstrating the procedures will be Iris Strzyzewski and Edward Traczyk, graduate students from my laboratory. To begin, prepare 50 milliliter sample vials. Place a label with the mulch, Kaolin, and companion plant treatment, the block number, and the sample date on the outside and inside of each vial.

Fill each vial with exactly 30 milliliters of 70%ethanol and place the vials into a tray. Take the trays to the experimental field site. Randomly assign the tomato or pepper plants to be sampled in each subplot.

Between mid morning and mid afternoon, obtain the samples from the upper half of the plant. Using a sharp-edged razor or scissors, carefully remove the flower from the plant and quickly place the flower into the appropriate pre-labeled vial. Collect 10 flowers per sample.

Make sure each vial is tightly sealed, then shake each vial to ensure that the flowers are submerged in the ethanol. Return the trays with samples to the laboratory and place the vials in a refrigerator to ensure the samples do not deteriorate prior to processing. Obtain the sample from the refrigerator, remove the lid of the vial and carefully remove with a pipette any excess alcohol above the flowers.

Reseal the vial and shake to dislodge the thrips and minute pirate bugs in the flowers. Open the vial and pour the contents into a Petri dish. Rinse the inside of the vial with 70%alcohol and pour the contents into the Petri dish.

Make sure all thrips and minute pirate bugs in the vial are flushed into the Petri dish. Dissect each flower with forceps and rinse with 70%alcohol to ensure that all the thrips and minute pirate bugs have been dislodged. Remove and discard the flower parts from the Petri dish.

Transfer the Petri dish to the plant form of a stereoscope with 40X to 150X magnification. With a 40X objective, identify a thrips larva which is smaller in size and lacks wings. Identify a female adult which is a larger size and has a cell-like ovipositor.

Count in each grid the number of adult males and females of each flower thrips species. Switch the magnification to 150X and identify the adult flower thrips species in Florida based on the setae on the pronotum, head and second antennal segment. Then position the adults and separate the adults of Frankliniella bispinosa from the adults of Frankliniella tritici and Frankliniella occidentalis by the extra stoutness of the two setae on the anterior dorsal margin of the second antennal segment.

Next, separate the adult Frankliniella occidentalis from those of those Frankliniella bispinosa and Frankliniella tritici by the near equal lengths of the anterior marginal and anterior angular major setae on the pronotum and by the longer 4th postocular setae on the head. To identify the minute pirate bugs in Florida samples, count in each grid the number of adult Orius insidiosus and Orius pumilio and the number of nymphal Orius species. Identify the adult Orius insidiosus by the brown basal antennal segments, by the femora that have dark markings, and by the that is dark brown.

Identify the nymphal Orius by the lack of wings and teardrop shape. Add the numbers from each grid to determine the total number of adult males and females of each flower thrips species, the number of Frankliniella species larva, the number of adult minute pirate bug of each species, and the number of minute pirate bug nymphs in the sample. In this protocol, the main effect of ultraviolet reflective mulch was significant for reduced number of female Frankliniella occidentalis with a p-value of less than 0.01.

While the main effects of Kaolin and companion plants were not significant for the female Frankliniella occidentalis with a p-value greater than 0.05. The effects of mulch on individual sample dates showed that the ultraviolet reflective mulch was effective in reducing flower thrips numbers early in the season but there was no significance on individual sample dates during mid or late season. Kaolin did not significantly affect female Frankliniella occidentalis numbers while male Frankliniella occidentalis numbers were significantly reduced.

The interaction of companion plant x sample date was significant for male Frankliniella occidentalis with a p-value less than 0.05 but not for female Frankliniella occidentalis with a p-value greater than 0.05. Companion plants reduced adult Frankliniella occidentalis numbers on late season sample dates but never on early or mid season sample dates. Numerous factors such as the time of day and the position of the flower on the plant influence sample estimates.

Therefore, it is critically important to know where, when and how to sample for thrips and minute pirate bugs. This procedure was used to develop a conservation biological control program using minute pirate bugs in strawberry. Other researchers are using these procedures to evaluate the effectiveness of these tactics in other crops and in other parts of the world.

The techniques have been instrumental in the development of push-pull strategies or cultural tactics such as ultraviolet reflective mulch and Kaolin pushed the thrips from the crops to a companion plant where they are eaten by minute pirate bugs.