How to Control Soil Insects with Beneficial Nematodes Ed Lewis Department of Entomology and Nematology University of California, Davis Using Microbials in IPM • Do not have to change everything about crop management • Many microbial insecticides fit into current production plans with minimal effort and change • They require specialized information about their use Insect pathogens can be effective • Naturally occur – Even in intensively managed systems • Have an impact on insect populations at natural levels Necessary information: Products • Shelf life • Storage conditions • Resting stage? • Viability in field • Host range • Time to kill • What does an infected insect look like? Recognized Species of Entomopathogenic Nematodes H. bacteriophora H. marelatus H. brevicaudis H. megidis H. hawaiiensis H. zealandica H. indica H. argentinensis S. kraussei S. karii S. arenarium S. kushidai S. bicornutum S. longicaudum S. carpocapsae S. monticolum S. caudatum S. neocurtillae S. ceratophorum S. oregonense S. cubanum S. puertoricense S. feltiae S. rarum S. glaseri S. riobrave S. intermedium S. ritteri S. affine S. scapterisci Infective Juveniles • Resistant to Environmental Extremes • Only Function is to Find A New Host • No Feeding • No Development • No Reproduction • Only Life Stage Outside the Host Infective Stage Juvenile Steinernema carpocapsae Symbiotic Bacteria Released Bacterial Chamber Mating for Steinernema spp. Two to three generations occur in a single host. About 6 days after the original infection, this is the appearance New Infective Juveniles in 10 Days Entomopathogenic Nematodes Can Control: • Weevils: Diaprepes root weevil, Diaprepes abbreviatus Blue green weevils, Pachnaeus spp. Otiorhynchus spp. Bill bugs • Fungus gnats: e.g., Sciaridae Entomopathogenic Nematodes Can Control: • Scarab larvae: e.g., Japanese beetle, Popillia japonica, Chafers, etc. • Lepidoptera: Black cutworm, Agrotis ipsilon Codling moth, Cydia pomonella Leafminers, Liromyza spp. Banana moth, Opogona sacchari Navel Orangeworm, Amyelois transitella • Other: fleas, mole crickets Some Things to Remember About Entomopathogenic Nematode Products Products Can Be Deceiving • Infective Stage is NOT a Resting Stage Live Infective Stage Nematodes Infective Stage Survival H. bacteriophora S. carpocapsae S. glaseri How Long Do They Last? Formulation Shelf-life (storage method) Sponge 2 Months (Refrigerated) Vermiculite 3-5 Months (Refrigerated) Dispersable Granule 2-5 Months (Room Temperature) How Do We Figure Out Where and When to Use them? • Climate • Soil Types Special considerations for applying microbials • Not chemical pesticides – Storage – Application • Special habitat requirements • Realistic expectations – Kill slower than chemicals – Will not (usually) completely eliminate pests Case Study • Entomopathogenic nematodes to manage Diaprepes abbreviatus (citrus root weevil) in Florida and California Citrus Root Weevil Adult Diaprepes Damage Southport Grove, Osceola County, FL What makes Diaprepes difficult to control? • 270 known host plant species • asynchronous, complex, variable life history • high fecundity, protected egg masses • many pesticides are ineffective against soil-dwelling larvae • many natural enemies have limited, patchy distributions Diaprepes abbreviatus Life Cycle Eggs Adults Neonates Pupae Larvae Nematodes Most Effective in Coarse Sandy Soils 100 Field Experiment + S. riobrave 80 Untreated 60 40 20 Percent mortality 0 Sand Sandy Clay Loam (Duncan et al., unpublished) What to do in California? • Soil type has major impact on efficacy • Soils in California much more diverse than in Florida Objective • Develop methods to determine whether or not entomopathogenic nematodes will be effective biological control agents of citrus root weevils in CA citrus Column Assay Units S. riobrave – Efficacy Bioassay 1000 10 cm 800 600 400 200 0 ±SE) ( 400 25 cm 300 200 S. riobravae 100 0 400 Number of 50 cm 300 200 100 0 1 2 3 4 5 6 7 8 9 1 11 12 13 14 1 16 17 18 1 20 21 22 23 2 25 26 27 28 29 30 31 32 33 0 5 Soils 9 4 8 7 28 30 31 Cluster 36 A 32 analysis: 24 26 4 grouped 15 16 similar soils 6 5 35 B based on 3 17 18 physical and 2 25 chemical 1 23 21 characteristics 34 C 14 27 29 33 9 19 20 22 D 11 10 12 13 S1 S2 S3 S4 S5 MR pH EC Silt OM Clay 600 (a) a 500 a 400 10cm b 300 c 200 100 percentile ) Efficacy of th 0 25 ± 120 EPNs in (b) b a 100 25cm different 80 60 c clusters 40 20 d 0 60 (c) a 50 50cm Median Number of Nematodes ( 40 b 30 b 20 10 c 0 A B C D Cluster Using This Information Can soilless media be constructed to enhance persistence and efficacy of microbial insecticides? 10 Foraging of S. riobrave in Soilless Media Components 0 8 a 25 ab 50 ab abc 6 abc abc abc abc abcd bcde bcde bcde 4 cdef def def f Distance travelled (cm) travelled Distance f f ef 2 f f f 0 Sand Peat Mos s Cedar/Pine Rec y c led Redw ood Redw ood Per lite Vermiculite Bark Plant Saw dust Saw dust Mater ial (w /o bark) (w /bark) How to Make EPNs Work? • Product quality • Product suitability • Application rates • Application timing • Environmental conditions • Substrate conditions .