Common names:White grubs, June beetles (female beetle), Chafers (female beetle), Root grubs, Gallina cieia (Spanish), Jaboto (Spanish), Chobote (Spanish), Abejon de mayo (Spanish), Chicote (Spanish)
Latin name:Phyllophaga and Cyclocephala spp.

Life cycle and description

• Adult stage: Adult beetles are pale yellow to dark brown, with a light brown abdomen. Legs are dark brown. Adult antennae are 10-segmented. Adults are 1.5 to 2cm long and 1.2 to 2.3cm wide. Females tend to be wider than males. Beetles emerge from pupae in the soil in response to the onset of the rainy season or soil disturbance (e.g. plowing). Adults typically emerge at dusk at temperatures between 27 and 30۫C and are active night fliers. Adults commonly feed in trees, but return to grasslands and cultivated fields to lay eggs following mating. Female adults can continue ovipositing for over 100 days. Up to 60 eggs can be oviposited at a time.
• Egg stage: Freshly laid eggs are oval, white, about 3mm long and 2 mm wide. After three to four days, eggs become spherical and smooth and are about 2mm in diameter. Mature eggs are brownish-black with a diameter of about 4mm. Eggs are deposited singly in weedy fields or grasslands several centimeters (5-15cm) below the soil surface. Duration required for eggs to hatch varies considerably from 6 days to over 50 days in some cases.
• Larval stage: Larvae are creamy white and C-shaped. They measure 2 to 3mm when young, but grow to nearly 4cm when mature. Mature larvae appear slightly swollen and semi-transparent. Larvae have prominent brown heads, mandibles, and five segmented antennae. Larvae have three pairs of spiny, well developed legs and a shiny tip to the abdomen. Larvae undergo three instar stages. Larvae may also undergo diapause prior to pupation. Wet soil conditions during diapause will cause high larval mortality.
• Pupal stage: Pupae are soft and white to yellowish in early stages, gradually becoming brown. Pupae generally occur in cells in the soil and range from 1.5 to 3cm in length. Width is typically about 1.5cm. Pupal development takes 30 to 40 days.
• Most species of white grub complete their lifecycle in one year; however, the most damaging species Phyllophaga implicita can take up to three years.

Confirmation

Examination of soil and roots of affected plants will reveal the characteristic white C-shaped grubs of varying sizes. Species can be confirmed by detailed examination of larvae setae or examination of genitalia of adult beetles. Due to the long life cycle, rearing of larvae to adulthood may not be practical.

Problems with similar symptoms

Wilting seedlings, poor plant stands and lodging can be caused by a variety of borers, seedcorn maggots, and damping off of seedlings by pathogens.

Why and where it occurs

Serious crop damage generally occurs when the crop has followed pasture, as the ovipositing beetles prefer weedy fields. Ovipositing generally occurs within 90m of trees in which adult beetles feed. Immature larvae prefer plants with shallow, matted root systems. Sandy loam and clay loam soils with a moisture content of 15-25% moisture content favor larvae and egg development. Adults disperse to uninfected areas by flight or through wind currents.

Host range

Maize, sorghum, rice, beans, potato, tomato, coffee, oats, wheat, barley, jasmine, Nerium sp., turf grass, pasture, red pine seedlings, Larix leptolepis, and tea.

Geographic distribution

Worldwide - but is a particular problem in North, Central and South America.

Damage

• Mechanism of damage: Larvae feed on root systems, resulting in wilting, poor absorption of nutrients, crop lodging and stunted plant growth. Adult beetles feed on the foliage of deciduous and coniferous trees. Sometimes just the petiole is eaten, causing the whole leaf to drop. However, this damage is generally not considered serious.
• When damage is important: Severe infestation can result in extensive loss of crop stand and poor plant growth. Damage is most serious when infestation occurs while plants are in the seedling stage.
• Economic importance: This species can cause massive crop losses. In Rajasthan, India, losses reaching 80% have been reported. The economic threshold in North Dakota is 1 larva per 0.304 m².

Management principles

Monitoring

• Adult populations can be monitored using light and pheromone traps.
• Incidence of larvae can be monitored by soil sampling to determine whether the larval population has exceeded the economic threshold.

Control

• Integrated pest management of white grubs should include:
  
  • Planting of resistant maize varieties.
  • Crop rotation with deep-rooted legumes such as alfalfa, sweet clover or other clovers. Maize may follow clover in the rotation, but should never follow grasses. Sunflower can also be used in rotation.
  • Promotion and conservation of natural predators and pathogens.
  • Reducing or pruning trees that attract adults bordering the crop.
  • Use of light and pheromone traps to trap adults prior to egg laying.
• Heavy nitrogen fertilization adversely affects first instar larvae.
• Trees that harbor adults can be sprayed with insecticide or shaken down to collect and destroy the beetles.
• Spores of the pathogens Bacillus popilliae and B. lentimorbus can be used to inoculate the soil.
• Effective parasitic wasps include Tiphia species, Myzinum species and Pelecinus polyturator, as well as the fly Pyrgota undata. Nematodes Metarhizium anisopliae and Steinernema glaseri have also been effective against white grubs
• Granular insecticide treatment of the soil can reduce larvae numbers in serious infestations. Application should occur when the grubs are immature, as the mature larvae often are quite deep in the soil and are very resilient. Granular soil treatment with fensulfothion, quinalphos, phorate, carbofuran or isofenphos during planting and 90 days later has been effective in suppressing white grubs. Granular treatment may not be necessary in the entire field and larvae numbers are typically highest near tree borders where adult beetles feed. Soil sampling should determine area of application.

References

CAB International. 2002. Crop Protection Compendium. Wallingford, UK. CAB International.

Davidson, R.H. and W.F. Lyon. 1987. Insect Pests of Farm, Garden and Orchard. Hoboken, NJ: John Wiley & Sons.

King, A.B. and J.L. Saunders. 1984. The Invertebrate Pests of Annual Food Crops in Central America. London: Overseas Development Admin.

Knodel, J. n.d. White Grub Management for North Dakota. NDSU Extension Service, North Dakota State University. http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/whitegrub/whitgrub.htm (24 Jan 2007).

Kuhlman, D.E. and R.G. Dedert. 1987. Insect Pests of Maize in Zambia. Urbana – Champaign, IL: University of Illinois

Ortega, A. 1987. Insect pests of Maize: A Guide for Field Identification. Mexico, D.F.: CIMMYT.

Sidebottom, J., J. Owen, D. Hundley and J. Neal. 1998. White Grubs. Scouting Fraser Fir in North Carolina. Publication AG 573. North Carolina Cooperative Extension Service, North Carolina State University. http://ipm.ncsu.edu/Scouting_Fraser_Fir/white_grubs.html (24 January 2007).

Contributors: Gabrielle Turner, David Bergvinson, and Biswanath Das