Kurt Put

Bombus terrestris as pollinator‐and‐vector to suppress Botrytis cinerea in greenhouse strawberry

BACKGROUND Bombus terrestris L. bumblebees are widely used as commercial pollinators, but they might also be of help in the battle against economically important crop diseases. This alternative control strategy is referred to as pollinator-and-vector technology. The present study was designed to investigate the capacity of B. terrestris to fulfil this role in greenhouse strawberry flowers, which were manually inoculated with a major plant pathogen, the grey mould Botrytis cinerea Pers.: Fr. A model microbiological control agent (MCA) product Prestop-Mix was loaded in a newly developed two-way bumblebee dispenser, and, in addition, the use of the diluent Maizena-Plus (corn starch) was tested. RESULTS Importantly, loading of the MCA caused no adverse effects on bumblebee workers, with no loss of survival or impairment of flight activity of the workers during the 4 week flowering period. Secondly, vectoring of Prestop-Mix by bumblebees resulted in a higher crop production, as 71% of the flowers developed into healthy red strawberries at picking (preharvest yield) as compared with 54% in the controls. In addition, these strawberries were better protected, as 79% of the picked berries remained free of B. cinerea after a 2 day incubation (post-harvest yield), while this percentage was only 43% in the control. Overall, the total yield (preharvest × post-harvest) was 2-2.5 times higher than the total yield in the controls (24%) in plants exposed to bumblebees vectoring Prestop-Mix. Thirdly, the addition of the diluent Maizena-Plus to Prestop-Mix at 1:1 (w/w) resulted in a similar yield to that of Prestop-Mix used alone, and in no negative effects on the bumblebees, flowers and berries. CONCLUSIONS This greenhouse study provides strong evidence that B. terrestris bumblebees can vector a MCA to reduce B. cinerea incidence in greenhouse strawberries, resulting in higher yields. Similar yields obtained in the treatments with Prestop-Mix and Prestop-Mix + Maizena-Plus suggest an equally efficient dissemination of the biocontrol agent into the flowers with only half the initial concentration of Prestop-Mix, which illustrates the importance of the diluent.

Development of a new dispenser for microbiological control agents and evaluation of dissemination by bumblebees in greenhouse strawberries

BACKGROUND To date, in modern agriculture, biological control strategies are increasingly becoming the preferred pest management approach. However, the success of microbiological control agents (MCAs) largely depends on efficient dissemination into the crop. The pollinator-and-vector technology employs pollinating insects like bees for a better dissemination. In this study, a new dispenser for bumblebee workers of Bombus terrestris L. was developed. Binab-T-vector and Prestop-Mix were used as two typical MCA products for dissemination. RESULTS In a first series of experiments in the laboratory for optimisation, the newly developed dispenser was a two-way type dispenser, 20 cm long, with two rectangular compartments and different entrance and exit holes. In addition, the amounts of MCA loaded on the workers were 10 times higher with the new dispenser as compared with the side-by-side passageway (SSP) dispenser. Typically, the highest amounts were recovered from the thorax and legs of the workers. In a second series of experiments under greenhouse conditions with the use of queen-right B. terrestris hives, successful dissemination in strawberry flowers was obtained at different distances from the hive (0-8 m, 8-18 m and 18-21 m), and the workers inoculated the first, second and third flowers that were consecutively visited. In addition, the new dispenser caused no adverse effects on worker foraging intensity, whereas a dramatic reduction was scored with an SSP dispenser. Finally, the data suggested that it is necessary to refill the newly developed dispenser at 3 day intervals. CONCLUSIONS The results demonstrated that, with the use of the newly developed dispenser, bumblebee workers carried high amounts of MCA, and this resulted in a successful dissemination of MCA into strawberry flowers.

Non-target effects of commonly used plant protection products in roses on the predatory mite Euseius gallicus Kreiter & Tixier (Acari: Phytoseidae)

BACKGROUND Euseius gallicus Kreiter & Tixier (Acari: Phytoseidae) is a predatory mite recently available for use against various pests in roses. We tested in greenhouse trials the impact on the numbers of eggs and motiles of E. gallicus of the most commonly used plant protection products in roses in northern Europe: the acaricides acequinocyl and etoxazole, the insecticides azadirachtin-A, acetamiprid, flonicamid, imidacloprid, indoxacarb, thiacloprid and thiamethoxam and the fungicides boscalid and kresoxim-methyl, cyprodinil + fludioxonil, dodemorph and fluopyram + tebuconazole. RESULTS The neonicotinoids thiacloprid, thiamethoxam, acetamiprid and imidacloprid had a negative impact on the number of eggs (47, 62, 81 and 76% reduction, respectively, compared with a water treatment) and number of motiles of E. gallicus (42.2, 42.9, 59.9 and 60.6% reduction) and were classified as slightly to moderately toxic. Also, the number of motiles was reduced after treatment with acequinocyl (47%) and etoxazole (43.9%) and after two treatments with flonicamid (41%) with a 1 week interval between treatments. CONCLUSION Azadirachtin-A, acetamiprid, flonicamid, boscalid and kresoxim-methyl, cyprodinil + fludioxonil, dodemorph and fluopyram + tebuconazole were harmless for E. gallicus. Special attention should be paid to the impact of neonicotinoids and of acequinocyl and etoxazole, and to the application frequency with flonicamid on E. gallicus.

Miniature-dispenser-based bioassay to evaluate the compatibility of powder formulations used in an entomovectoring approach

BACKGROUND Entomovectoring as a plant protection strategy demands the design of an appropriate bioassay to assess the risks of potential side effects of the powder formulations in the dispenser towards the vectoring insect. This study reports on the development of a laboratory miniature-dispenser-based bioassay. This bioassay system was used to investigate the compatibility of five model products, Prestop-Mix, Signum, kaolin, wheat flour and cellulose, with the bumblebee, Bombus terrestris L. RESULTS The laboratory one-way miniature-dispenser bioassay showed that the fungicides and the carrier/diluent kaolin caused a worker mortality of > 70% after 5 weeks of exposure, while worker loss with wheat flour and cellulose was no higher than in the blank control (i.e. empty miniature dispenser) (<25%). The laboratory two-way miniature-dispenser bioassay comprised separated passageways and demonstrated that only kaolin was toxic (89 ± 11%). These results were also confirmed in a flight-cage experiment. In addition, a negative effect was observed against reproduction/colony development when nests were exposed to kaolin (P < 0.05) in the two-way miniature-dispenser and flight-cage bioassays. CONCLUSIONS In the context of entomovectoring technology, the developed laboratory two-way miniature-dispenser bioassay gives a reliable prediction of the hazards associated with powder products. Additionally, the present data indicate the possibility of using cellulose and kaolin as respective negative and positive control carriers/diluents in future risk assessment experiments. Overall, the results show that, apart from kaolin, the tested fungicides and carriers/diluents are safe to be used with B. terrestris.