Tara P. Smith, Abner M. Hammond, Craig A. Abel, Michael J. Stout and B. Rogers Leonard
The first reported damage by the sugarcane beetle, Euetheola humilis
, to crops in the United States was in Louisiana sugarcane plantations during 1880. Since that time, this beetle has been documented as an occasional pest of field corn, rice and more recently sweet potato. Historical crop damage reports related to this pest have varied through the decades, and reports of damage to seedling corn plants have been more common in recent years. Sugarcane beetle damage to sweet potato was reported for the first time in 2001, and several Louisiana sweet potato growers have suffered significant losses from this insect in recent years.
The adult beetle appears to be the most common stage that causes crop injury as it feeds beneath the soil surface on root tissue. Damage to sugarcane, field corn and rice often results in death of the plants. Sugarcane beetles gouge holes in sweet potato roots, and damage is often confused with that of a more familiar pest, the white grub. Feeding damage from the beetles (Figure 1) compromises the aesthetic quality of the roots, rendering them unmarketable.
Sugarcane beetles have one complete generation each year. They overwinter as adults and become active in the spring as soil and air temperatures increase. These beetles can injure corn seedlings in early spring but will continue feeding on corn plants up to 4 feet tall. Sugarcane beetles emerge in the spring and early summer, mate and lay eggs in the soil. Larvae develop in June and July, and a new generation emerges from August through September. Recent research suggests that this newly emerged generation damages sweet potatoes prior to harvest.
Granular soil insecticides and some insecticide seed treatments have been shown to reduce sugarcane beetle infestations in corn; however, no insecticides are currently labeled to control this beetle in sweet potato. Researchers have limited information on the ecology and biology of the sugarcane beetle, probably as a result of its sporadic occurrence. The recent increase in reports of damage to Louisiana corn and sweet potatoes suggests that additional research is warranted.
A series of experiments were conducted in LSU AgCenter greenhouses in Baton Rouge in 2003 and 2005 to investigate sugarcane beetle feeding on known host plants. Seven different plant species – sweet potato, sugarcane, corn, Bt corn (corn with a gene from Bacillus thuringiensis
, a bacterium toxic to some insects), strawberry and Bermuda grass – were evaluated as host plants. Plants of each species were maintained in the greenhouse and transferred to plastic tubs for a selective feeding choice test. The tubs were divided into seven sections with plexiglass partitions. Fresh potting soil was placed in each tub level with the tops of the plexiglass, and plants were assigned randomly to each section. Two plants each of sweet potato, sugarcane and strawberry were placed in a section. Two groups of six seedlings each (12 seedlings per section) of corn, Bt corn and rice were planted in a section. Corn and rice used in the experiments were 6 to 12 inches tall. Bermuda grass was transplanted to totally cover a section. After transplanting the plants, the soil was leveled across all sections and the plants were watered. Five replications (one per tub) were conducted each year.
Sugarcane beetles were collected using black light traps and were starved 48 hours before each test. Six beetles were placed in each section of a tub; three grouped around each plant or clump of plants. After all beetles had burrowed into the soil, hardware cloth was secured across the top of the tub to prevent their escape. The insects were allowed to feed and move freely for 96 hours. To make a choice, beetles had to leave one host plant and then search and find an alternative host plant by moving across plant sections and burrowing into another section; however, they could not move underground between sections because of the plexiglass dividers. At the end of 96 hours, the hardware cloth was removed, the soil from each section of each grow tub was sifted, and the number of beetles per section was recorded.
Sugarcane beetles fed on all plants evaluated; however, the majority of beetles were recovered from sections containing sweet potato, corn or sugarcane plants. In 2003, 36 percent of the beetles were recovered from sweet potato sections and 29 percent were recovered from sugarcane sections (Figure 2). In 2005, more beetles were recovered from corn, 33 percent, than any other plant evaluated. However, 18 percent of the beetles were also recovered from Bt corn and 19 percent were recovered from sweet potatoes. These data are consistent with recent field observations of sugarcane beetle damage. Most damage reports from this insect in the past five years have been in sweet potatoes and corn.
LSU AgCenter scientists are monitoring the pest status of this beetle in both corn and sweet potatoes. New and innovative strategies will be required to manage this pest because of its biology and behavior. Research projects are currently focused on identifying a sampling technique to monitor adult populations and evaluate insecticides that might fit into the overall integrated pest management programs in those crops where it proves to be a pest. Tara P. Smith
, Assistant Professor, Sweet Potato Research Station
, Chase, La.; Abner M. Hammond, Professor, Department of Entomology, LSU AgCenter, Baton Rouge, La.; Craig A. Abel, Research Leader, USDA-ARS Southern Insect Management Research Unit, Stoneville, Miss.; Michael J. Stout, Associate Professor, Department of Entomology, B. Rogers Leonard, Professor, Macon Ridge Research Station, Winnsboro, La.