Metarhizium Spray on Brown Marmorated Stink Bug Nymphs and Lace Bug Adults in 2015

The objective of the study was to evaluate a commercial Metarhizium (Met52 EC) product when sprayed directly onto nymphal brown marmorated stink bug (BMSB), Halyomorpha halys Stål, and adult azalea lace bug, Stephanitis pyrioides Scott. BMSB is a polyphagous pest of many agricultural and ornamental crops, and the azalea lace bug is a pest of azaleas and rhododendrons, Rhododendron spp. BMSB nymphs and lace bug adults were collected from multiple sites in the Willamette Valley of Oregon. Five BMSB nymphs of unknown sex were placed in a 85- × 23-mm Petri dish per replication with eight water (check) and eight Met52 EC dishes of small nymphs (3rd–early 4th instars), and 20 water (check) and 19 Met52 EC replicates of large nymphs (late 4th and 5th instars). Five female and five male adult lace bugs were in each Petri dish per replication for a total of 15 water (check) and 15 Met52 EC replicates. Sprays were tested between 29 Jul and 5 Aug 2015 for BMSB, and between 4 and 21 Aug 2015 for lace bugs. Insects were sprayed with Met52 EC (Novozymes Biologicals, Inc., Salem, VA), which contains an 11% solution of Metarhizium brunneum (=anisopliae) strain F52 spores. The solution was mixed the same day of spraying at 7.81 ml per liter of water (1 fl oz/gal water). Insects were chilled on ice and then both species were sprayed with 2 ml of the solution or sterilized water with a Potter spray tower (Burkard Scientific, Uxbridge, UK) at 15 psi. After spraying, the insects were transferred to a new ventilated plastic container with a water wick and food at 26°C, 16:8 (L:D) h, and 40%–50% relative humidity. BMSB were held in a 16 fl oz container with carrots and peanuts, and lace bugs in a 32 fl oz cup with azalea clippings. The number dead was recorded at 2, 5, 7, 9, 12, and 14 d after treatment (DAT). Dead insects from Met52 EC sprays were incubated at 26°C and 0:24 (L:D) h to confirm sporulation. Treatment, day, and treatment × day (and instar for BMSB) were fixed effects, and the replicate was the random effect. The model was fitted with a binomial distribution, autoregressive correlation, and included Kenward–Rogers adjustment for degrees of freedom. The cumulative proportion of dead insects were analyzed using repeated measures with the SAS procedure, GLIMMIX. Means were separated within DAT by Tukey’s mean separation (P = 0.05).

For BMSB, while there was significantly higher mortality with Met52 EC spray from 7–14 DAT (Table 1), it was only a ~26% increase over the untreated check at 14 DAT. In the Met52 EC spray, over half of (51 out of 100) BMSB nymphs molted to adults and one laid eggs. While 54% of the Met52 EC-sprayed BMSB sporulated, it took 9 d before 56% of them died. The 39% mortality in the untreated check was expected because BMSB nymphs reared on suitable foods in ideal lab conditions have >20% mortality at each nymphal stage and nymphs are sensitive to handling. For lace bugs, mortality was not significantly different between Met52 EC and untreated check (Table 1). Although 80% of the Met52 EC-sprayed lace bugs sporulated, it took 9 d before 55% of them died. Moreover, 83% from the untreated check died by day 14 which led us to later examine water sprays on these delicate insects. In a separate trial conducted in a similar setup, 56% of lace bugs died from water sprays and 22% in the unsprayed check (Lee, unpublished data). These trials confirmed that both insects are susceptible to the product. Moderate control might be achieved in the field with an air blast direct spray that covers the underside of leaves where both insects are found. However, this spray is not an effective option for either pest when growers could use more effective measures. Other modes of delivering Met52 EC to BMSB may warrant study, such as attracting BMSB to a station where they are inoculated with spores.

This research was supported by industry gift of pesticide and research funding and was assisted by C. Alba, A. Cave, and A. Lake.