Predation test results and dynamics between three species of soil-dwelling predatory mites and early stages of maize pest.

PREDATORY MITES

                The three species used in this experiment were stored in climatic chambers at 25°C +/- 0,5°C and 70% +/- 10 RH% with constant obscurity. A mix of Aleuroglyphus ovatus stages was used as food and extra water was provided three times a week in a 100 mm x 94 mm bugdorm-5002 with 30µm nylon screen port sold by Bugdorm©.

Macrocheles robustulus

                Koppert Biological systems provided Macrocheles robustulus. Their product is called Macro-mite©. We maintained them on vermiculite for 2 months with a mix of A. ovatus stages.

Gaeolaelaps aculeifer

                Gaeolaelaps aculeifer is produced by EWH Bioproduction, Denmark. The population was maintained during 8 months on a substrate made of 1/3 third blond sphagnum peat and 2/3 of fine vermiculite and fed with a mix of A. ovatus stages.

Stratiolaelaps scimitus

                Stratiolaelaps scimitus individuals used in this experiment are produced by Bioline AgroSciences. The product is called Hypoline©. This population has been maintained on blond sphagnum peat and fed with a mix of A. ovatus stages for 2 years.

PREYS

                We experimented eggs and first instar larvae for both Diabrotica virgifera virgifera and Agriotes sordidus as potential prey. We also added Aleuroglyphus ovatus eggs as a positive control of predation activity since astigmatid mites are known to be a suitable food source for those species (Rueda-Ramirez et al. 2018).

Diabrotica virgifera virgifera eggs

                WCR diapausing eggs were provided by the Centre of Agriculture and Bioscience International (CABI), Hungary. They were stored at 7°C +/- 0,5°C below their temperature of development (Meinke et al. 2009). We sieved the eggs from their substrate and selected only turgescent eggs to offer them to the predatory mites.

Diabrotica virgifera virgifera first instar larvae

                 We placed WCR eggs on the plaster of Paris in a climatic chamber at 25°C +/- 0,5°C and 70% +/- 10 RH%. We added water twice a week to keep the plaster of Paris moist. We checked daily if eggs hatched and introduced the first instar larvae in the predation device.

Agriotes sordidus eggs

                Arvalis provided Agriotes sordidus eggs and first instar larvae by sending us a couple of adults ready to lay eggs in Petri dishes filled with a sample of soil where they have been collected. Both eggs and first instar larvae have been extracted from this dirt.

Aleuroglyphus ovatus eggs

                A. ovatus eggs are produced by Bioline AgroSciences. Eggs were sterilized before presentation to the predatory mites.

Ephestia kuehniella eggs
 

               E. kuehniella eggs are produced by Bioline Agrosciences. Eggs were sterilized before presentation to the predatory mites.

                PREDATION DEVICE

                Predation tests have been inspired by El Adouzi, Bonato, et Roy 2017; Lovis et al. 2011 and Nordenfors et Hoglund 2000 protocols by isolating each mite individually. However, we chose to carry out the predation tests in 2 mL Eppendorf tubes containing each 1 mL of dried plaster of Paris to maintain a high percentage of humidity necessary to soil-dwelling predatory mites survival (El Adouzi, Bonato, et Roy 2017). Adult mites of both sexes were individually isolated and starved for 7 days in the tubes before the predation tests. In total, 240 predatory mites have been isolated with 1/3 of each species to present them to 4 different types of prey. Twenty predation tests were made by prey/predator couple.   
                During the 7-days period of starvation, we added 100µL of water every 3 days to maintain a suitable relative humidity necessary for soil-dwelling predatory mites survival. We also drilled the top of the tube and covered it with a 106 µm mesh width nylon tissue. This size of mesh allowed for water and gas exchange while preventing mites from leaving the tube. These tubes were stored in a climatic chamber at 25°C +/- 0,5°C with 70% +/- 10% RH.  All three species were active after this period of storage and starvation.

                We introduced 20 times one prey in a tube containing a predatory mite and observed predation activity during a maximum of 10 minutes or less if predation happens before that timing. We observed each mite feeding or non-feeding activity through the tube with a binocular. We used an indirect source of light, controlled at 100 lux (measured with the Digital Illuminance meter TES 1335), to minimize natural behavior disruption of these lucifugous species. During each assay, the timing and number of contacts between the predator and the prey before predation were noted. We considered predation activity when mites impaled the prey with their chelicerae. We chose to observe predation on a short duration because some of the prey could be impacted by plaster of Paris abrasive texture if it dries up.