Integration of Tools for the Control of Drosophila suzukii
The spotted-winged fly ( Drosophila suzukii Matsumura ) is considered an invasive pest that constitutes a serious economic threat in various fruit trees, as has begun to occur in Chile. During the 2019/20 agricultural season, losses of 4,000 to 17,750 dollars per hectare were reported in some blueberry and cherry orchards in the Ñuble Region (Buzzetti, 2020), a situation that could be increased and extended to other fruit trees with the recent advance of the plague in other regions.
The economic losses associated with D. suzukii are mainly due to the damage generated by oviposition in fruits, which is usually carried out by one or more females on the same substrate from when the fruit begins to turn color onwards. It can lay several eggs per fruit, and continue to damage neighboring fruits to the larval stage.
Unlike other drosophilids, the spotted-winged fly oviposits on healthy fruits, recognizing that it prefers to lay on fruits with soft and thin skin, close to a pint or the beginning of maturity. It is extremely polyphagic, globally reporting hosts that vary from berries, stone fruit, grapes, tomatoes, wild species and ornamental plants, among others; It also has a high fecundity (it can produce up to 600 eggs per female), with an extremely short generation time, taking from egg to adult between one to two weeks.
Due to its high capacity to present resistance to insecticides, the need for complementary tools that support its management is foreseen, a line of research in which the use of meshes, mass capture traps, protectors of fruits based on phospholipids or diatoms, among other tools, with some conclusive results but still limited in applicability or extrapolation due to lack of local experiences for the Chilean case.
In this context, the objectives of the present study were proposed: 1) to inquire about the level of effectiveness of the use of traps adapted for mass capture of adults; and 2) study on the predisposition of D. suzukii females to oviposit in fruits treated with a phospholipid-based biofilm under the commercial formulation Parka®.
This test stage was carried out during the 2019/20 season in a cherry orchard located in the Ñuble Region, in an area registered as positive for the presence of D. suzukii according to records of the Agricultural and Livestock Service (SAG), and that later it was confirmed with incidence of damage in fruits during the same season. We worked with traps of the Flybuster® model and with homemade glass (or bucket) traps with a red lid with 4 mm diameter holes and a spacing of 2 cm between them (SAG, 2017). In both, the volume of capacity corresponded to 1 liter (standardized). The type of baits and the treatment combinations are summarized in Table 1.
In all the treatments, the equivalent of four traps / hectare was used, distributed in a square format outside the orchard. The location of the treatments was randomly drawn, establishing a completely randomized design with four repetitions (of 1 hectare each) and six evaluation moments (at 4, 6, 9, 10,14, 20 days after installation, the which have been summarized as the sum of adults captured in 20 days post installation). The traps were installed in pint and postharvest of the fruit tree (May 20, 2020), with independent evaluations.
The variables evaluated in each measurement were: number of adults of D. suzukii captured in trap (total and separated by sex) and number of other insects (total and by species) captured by trap.
In two orchards located in the Ñuble Region (one of cherry trees and the second of blueberries), both positive for the presence of the pest and with damage evidenced from the beginning of the pinon fruit, the treatments set out in Table 2 were carried out.
Each treatment was randomly drawn with 4 repetitions of 20 plants each, with subsequent measurements at each moment of application aimed at establishing, at 9 days after the first application (DDA-I) and at 9, 10, 12, 14 days after the second application (DDA-II), the total of infected fruits and the total ovipositions of D. suzukii in fruits.
For all studies, the data were analyzed in order to determine compliance with the ANDEVA assumptions, and establish, if required, the use of appropriate statistical transformations. To define the possible differences between results obtained according to treatments, the Tukey multiple comparison test was used (p: 0.05).
In order to confirm the identification of the specimens involved in all the tests carried out, traditional taxonomy techniques supported by molecular identification were used.
MASS CATCH TEST RESULTS
For all the treatments evaluated, the highest capture rate occurred in the post-harvest period, which would respond to the lack of competition between food attractants and the presence of fruits. The most efficient combination in capturing adults of D. suzukii was the use of Flybuster with its own bait (of the same name), followed later by the homemade trap with Flybuster bait, (always the bait diluted in 50:50 water and vinegar of Apple cider). Compared to the previous ones, the combinations with attractant of domestic manufacture were less efficient in capturing adults (Figure 1).
The ratio of females: males captured of D. suzukii did not present significant differences between treatments. Regarding the selectivity of the treatments, contaminating insects were found in equivalent quantities, but of different composition, in all the combinations of traps evaluated. For the same measurement period, Flybuster captured mainly mosquitoes (Diptera: Culicidae) and house flies (Diptera: Muscidae), while the glass-type home trap captured other drosophilids (especially D. melanogaster), making it difficult to correctly identify the adults with traditional macroscopic taxonomic techniques. given the degree of similarity to the target species.
In future works and some currently in progress, the proposed evaluations are expanded by combining other interactions such as the color of the trap and design, as well as the direct impact of the use of these traps on measurement parameters of direct damage to fruits, but for now it is achieved establish a promising advance in the level of adult captures of D. suzukii in conditions of productive orchards in Chile, which would support a control program with conventional techniques such as the application of pesticides.
TEST RESULTS OF FRUIT PROTECTORS
The use of Parka® in cherry trees and blueberries produced a decrease (expressed as a percentage at the end of the evaluated period) in the average number of fruits damaged by oviposition of the spotted wing fly by 54-68% respectively compared to the control; and 59% -63% less severity of the attack when determining the average oviposition in cherries and blueberries versus the control treatment (data not shown).
Regarding the effectiveness as a single control, what has been achieved with the use of Parka® is evidently exceeded by the use of chemical treatments; however, these are products with different primary purposes. On the other hand, it should be noted that, despite the fact that some insecticides such as Imidan 70 WP or Invicto 50 CS may report a longer period of protection over other insects, regarding D. suzukii there is a shorter period of effectiveness due to the rapid Reinfestation that occurs with a new population of adults of different origins (high migratory rate), which, if they manage to land and lay eggs on the fruit, rapidly register a new incidence of damage to the crop (Figure 2).
Under these conditions, in the case of Invicto 50 CS, the control was adequate for at least ten days, similar in behavior to that observed for the control of D. suzukii achieved with another microencapsulated formulation of l-cyhalothrin previously studied (Karate® Zeon). (Buzzetti, 2020). For both formulations of l-cyhalothrin, a maximum interval between applications of twelve days would be suggested, in order to avoid a rebound in the infestation.
In the case of Imidan 70 WP, control against D. suzukii damage was appropriate in blueberries, which would allow a simultaneous control of various pests of agricultural interest at intervals between 12 to 14 days for the dose evaluated (Figure 3).
It is estimated that, for the period in which the applications of these tests were developed, at least two complete generations of D. suzukiiwere completed. A relevant factor to consider in the quantification of damage attributable to the attack of the spotted-winged fly is the increase in the expression of latent infections in asymptomatic fruits, due to the fact that it generates wounds in the cuticle of fruits, either due to the effective posture of eggs or by the attempt to oviposit when the fruit receives treatments whose mechanism of action does not affect adults (due to mortality, paralysis, repellency or other means). This increase in the expression of rots could be masked by being attributed solely to failures of a disease treatment program, even when it is also related to the attack of the pest.
Considering that each female of the spotted-winged fly has a high reproductive capacity, and that, as already mentioned, this pest can attack the same fruit several times or different females attack the same fruit, the results obtained in this work pose a great opportunity to complement a phytosanitary program, since, according to the company, the function of Parka® as a phospholipid-based biofilm is not related to the management or mortality of pests but to the protection of the fruit against adverse climatic effects such as a split due to rain or sunburn, which would allow that, pursuing the main objective for which the product is recommended, an improvement could be achieved in a phytosanitary program associated with this pest and, collaterally, with the expression of rot.
For this reason, the evaluations of combined treatments between this formulation and different insecticidal tools are projected in future works, in order to establish possible interactions that favor the management of the pest, and how they are inserted, in conjunction with tools such as mass capture, in an integrated pest management program that does not focus on the overuse of pesticides.
By: Karina Buzzetti , Doctor in Agricultural Sciences, Agri Development Consultant and Ian Homer , Doctor and Professor at the Faculty of Agronomic Sciences, Universidad De Chile
Buzzetti, 2020. “The Spotted Wing Drosophila in the South of the World: Chilean Case and Its First Productive Impacts”. Available at: https://api.intechopen.com/chapter/pdf-preview/71435 . SAG, 2017. Work plan for the Surveillance and Integrated Management of the pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in productive orchards and host fruit processing places.
This research was financed exclusively by the research team, which is part of an ongoing macroproject whose results are in the process of analysis. The authors declare that they do not receive commission for the sale or promotion of the products involved in the publication. Thanks to Pablo Silva Warner and Jorge Lundstedt for their technical guidance in the design of this work.