Efficacy of entomopathogenic fungi in an integrated pest management plan for cucumber beetles in melons and pumpkins

View the project final report

• 2010 annual report

Commodities

• Vegetables: cucurbits

Practices

• Crop Production: biological inoculants
• Pest Management: biological control, biorational pesticides, disease vectors, integrated pest management, physical control
• Production Systems: organic agriculture

Funds from SARE were used in 2011 for my dissertation research project to examine the efficacy of biopesticides for potential organic pest management of cucumber beetles on melon and pumpkin crops in the Southeastern U.S. Cucumber beetles are an annual pest on cucurbit crops and can damage pumpkin, cantaloupe/muskmelon, summer squash, cucumbers and watermelon. In addition to vectoring bacterial wilt, beetles chew stems, leaves and feed directly on fruit, reducing both marketable yield and quality. Organic growers are limited in what they can use for cucumber beetle management and need alternatives, and consumers increasingly demand vegetables that are grown chemical-free. Biopesticides made from naturally occurring microorganisms that kill the insect pest while preserving beneficial insects are worth exploring. This project evaluated the efficacy of three different mycoinsecticides in reducing cucumber beetle damage in an attempt to offer sustainable IPM guidelines suitable for small to medium sized growers in our region. The biopesticides tested were: 1. MBI-203, an early stage product under registration by Marrone Bio Innovations (Davis, CA), comprised of secondary metabolites isolated from a bacteria, Chromobacterium substugae; 2. Mycotrol O, a commercially available strain of Beauveria bassiana strain GHA (Laverlam International Corporation, Butte, MT) labeled for use on cucumber beetles; 3. Beauveria bassiana strain 11-98; 4. Isaria fumosorosea 3581 (a fungal strain known to infect cucumber beetles but has not been tested). These substances were tested for efficacy in the lab, and compounds 1, 2 and 4 were used in field testing.

Introduction

Cucumber beetles are annual pests on cucurbits and are difficult to manage due to alternative hosts of larval and adult stages and are highly mobile. The options for organic growers are limited and include crop rotation, use of reflective mulches, kaolin clay, nematodes, Beauveria bassiana and pyrethrins to manage these beetles. The efficacy of some of these methods is questionable. Conventional chemicals are effective but can have negative effects on the applicator, can pollute groundwater and may impact aquatic organisms as well as beneficial insects and pollinators. Consumer demand is moving increasingly toward chemical-free produce, and growers need to use a variety of strategies to minimize pesticide use to avoid environmental effects and pest resistance.

Both spotted (Diabrotica undecimpunctata) and striped cucumber beetles (Acalymma vittata) vector bacterial wilt. The spotted cucumber beetle, Diabrotica undecimpunctata howardi, is also serious pest of field crops. Larvae are known as southern corn rootworm and feed on roots of corn in the soil. Adults may defoliate plants of the Curcurbitaceae such as cantaloupe, cucumber, squash and watermelon; other host plants include corn, soybean, beans and sweet potato. The striped cucumber beetle, Acalymma vittata, has similar host preferences in the field to the spotted cucumber beetle, described above, however it is considered a cucurbit specialist (Bach 1980; Ellers-Kirk and Fleischer 2006), and larvae only develop on cucurbit roots (Bach 1980). Adults are long-lived; surviving up to 125 days, and females may lay up to 4 eggs per day (Ellers-Kirk and Fleischer 2006). Similar to the spotted cucumber beetle, there are two generations per year of A. vittata in the southern U.S. (Ellers-Kirk and Fleischer 2006).

The inundative use of entomopathogenic fungi should not be thought of as a therapeutic control like a typical chemical pesticide, but rather, as a form of biological control that should be used in tandem with other management practices, such as using insect predators and parasitoids and other cultural techniques (Jaronski 2009). Successful control can only be achieved by “winning the numbers game,” where infective propagules are introduced in sufficient numbers to reduce pest populations, a feat that is easier accomplished in a controlled greenhouse setting rather than in the field (Jaronski 2009). Therefore it is practical to begin research on biopesticides in a laboratory setting before moving to the field. Environmental factors can constrain efficacy of biopesticides and applied research to investigate the practicality of using these pathogens in agricultural pest management strategies focuses on the effective formulation and dispersal of infective propagules in the field and whether this is economically feasible (Jackson et al. 2010). This graduate student grant helped fund laboratory and field efficacy studies on 1. MBI-203,comprised of secondary metabolites isolated from a bacteria, Chromobacterium substugae; 2.Mycotrol O, a commercially available strain of Beauveria bassiana strain GHA; and 3.Isaria fumosorosea 3581.

• Literature cited

1.Determine the efficacy of of early stage biopesticide MBI-203 on cucumber beetles using a laboratory bioassay.
2.Determine the efficacy and virulence of Beauveria bassiana (Mycotrol-O and Bb11-98) and two strains of Isaria fumosorosea (3581 and 1506) on cucumber beetles using a laboratory bioassay.
3.Examine the efficacy of early stage biopesticide MBI-203 in managing two species of diabroticite beetles (Diabrotica undecimpunctata and Acalymma vittata) and effects on yield of melon and pumpkin plants in the field.
4.Compare two different rates of the novel biopesticide MBI-203 with the label rate of Beauveria bassiana (Mycotrol O) and Carbaryl (Sevin 80 S).
5.Determine if beetle densities are reduced by alternating commonly used plant protectants with MBI-203 in an integrated pest management program for sustainable melon and pumpkin production.
6.Examine the efficacy of entomopathogenic fungi Isaria fumosorosea strain 3581 in managing two species of diabroticite beetles (Diabrotica undecimpunctata and Acalymma vittata) and effects on yield of melon and pumpkin plants in the field.
7.Examine the potential of row covers to reduce cucumber beetle populations in melon and pumpkin plants before flowering, and effects on yield.