Biological control of Echinothrips americanus Morgan (Thysanoptera: Thripidae) in sweet pepper using the predatory thrips Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae)

Echinothrips americanus Morgan (Thysanoptera: Thripidae), also known as poinsettia thrips, has invaded several parts of the world becoming an important pest in many vegetable and ornamental crops. While biological control methods using predatory mites and bugs have been effective against flower-dwelling thrips, they have shown limited success against leaf-dwelling thrips like E. americanus. Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae) is a leaf-dwelling predatory thrips, that may offer a more effective solution due to its overlapping habitat with E. americanus which increases the likelihood of predator-prey interactions. This study aimed to evaluate the potential of F. vespiformis for controlling E. americanus populations in sweet peppers under greenhouse conditions. We also investigated whether supplementing the releases of the predator with Artemia franciscana Kellogg (Branchiopoda: Artemiidae) cysts would enhance the pest control efficacy of F. vespiformis. Our results showed a 93% decrease in the total E. americanus population with releases of F. vespiformis alone and a 98% decrease when the releases of F. vespiformis were supplemented with A. franciscana cysts, both of which were statistically significant compared to the control treatment. There was no significant difference between the two F. vespiformis treatments. Similarly, the abundance of both adults and immature stages of E. americanus was significantly reduced in the presence of F. vespiformis, regardless of the addition of supplementary food. Overall, these findings highlight the potential of F. vespiformis for the biological control of E. americanus and probably other leaf-dwelling thrip pests in sweet peppers.

Methods
Experiment Description
Conditions:

Temperature (°C): Average temperature of 17.3 ± 0.04 °C (min 9.1 °C, max 35.0 °C).
Relative Humidity (RH%): Average 68.1 ± 0.14% RH (min 22.5%, max 93%).
Lighting: Supplemental lighting is provided by four high-pressure sodium (HPS) lamps (400W), turned on from 5 am to 4 pm daily.
Cage Dimensions: Cages were 1.8 m wide, 2.5 m long, and 2 m high, covered with a thrips-proof screen net with a double door and zipper entrance. There were two rows, one with eight cages and another with four cages.

Experimental Setup:

Plant Species: Eight sweet pepper plants per cage, placed in a 0.5 x 0.5 m grid. The plants were 1.45 m high and without flowers.
Insect Species: E. americanus adults were introduced to each cage on October 26. F. vespiformis adults were released into certain cages on November 17 and again on November 24. 

Treatments:

The experimental setup involved four treatments with 3 replicate cages per treatment: Control: Sweet pepper plants infested with E. americanus.

F. vespiformis only: Cages where 10 adult F. vespiformis were released per plant. F. vespiformis + A. franciscana cysts: Cages where 10 adult F. vespiformis were released per plant, plus 0.1 g of A. franciscana cysts. A. franciscana cysts only: E. americanus was present, and 0.1 g of A. franciscana cysts were added per plant. 

Timeline:

October 26, 2022: 10 E. americanus adults introduced per plant in all cages.
November 17, 2022: First release of F. vespiformis adults.
November 24, 2022: Second release of F. vespiformis adults.
December 2 and 14, 2022: Additional applications of A. franciscana cysts.

Randomization:

The experiment followed a randomized complete block design with a total of 12 cages.