Panicle-Feeding Bugs: Rice Stink Bug, Oebalus pugnax (Fabricius); Southern Green Stink Bug, Nezara viridula (L.); Conchuela, Chlorochroa ligata (Say); Leaffooted Bug, Leptoglossus phyllopus (L.); False Chinch Bug, Nysius raphanus Howard

Description and Biology: Several species of true bugs, primarily stink bugs, may move in relatively large numbers from cultivated and noncultivated host plants to sorghum during kernel development. The bugs usually have a clumped distribution in a field.
The rice stink bug is one of the more common stink bugs infesting sorghum. Adults are straw-colored, shield-shaped, and 12 mm long. The insect overwinters in the adult stage in grassy areas. Approximately 10 to 47 light green, short, cylindrical eggs are laid in a cluster of two rows. Eggs hatch after five days. Nymphs require 15 to 28 days to become adults. The rice stink bug has many hosts, but shows a distinct preference for grasses.
The southern green stink bug is 19 mm long, green in color, and mostly shield-shaped. Females deposit 300 to 500 eggs in clusters of 30. The eggs hatch in about seven days, and the adult stage is reached in about six weeks. Generations occur at five- to six-week intervals and there are three to five generations per year. Adults live 40 to 60 days, or all winter as they overwinter in this stage protected under litter, bark, or other material.
The conchuela is a stink bug that varies in color from dull olive to ash gray. The most characteristic markings are orange-red bands along the lateral margins of the thorax and margins of the wings, and a spot of the same color on the back at the base of the wings.
The leaffooted bug is brown, oblong, and about 20 mm long. A white band extends across the front wings. Tibiae of the hind legs are dilated or leaf-like. Eggs are laid in flattened rows of 15 to 35 eggs. Nymphs are reddish.
The false chinch bug is uniformly gray to brown in color and about 3 mm long. The insect occasionally migrates in large numbers from wild hosts to sorghum fields, but infestations usually are concentrated in small areas of the field.

Symptoms and Damage: The bug species described above have similar nature and symptoms of damage. These bugs suck juices from developing sorghum kernels and, to a lesser extent, from other panicle parts. They may cause economic damage, depending on the number of bugs per panicle, duration of the infestation, and stage of kernel development when infestation occurs. The number of bugs that will reduce grain yield varies according to the species of bug and stage of kernel development when infestation occurs. Bugs cause more damage during early kernel development and less damage as kernels develop to the hard-dough stage. Both nymphs and adults can reduce kernel weight, size, and quality. Fungi often infect damaged kernels, causing them to turn black and be further deteriorated in quality. Damaged kernels rarely develop fully and may be lost during harvest with mechanized equipment.

Rice Stink Bug

Rice Stink bug

Southern Green Stink Bug

Southern Green Stink Bug

Conchuela

Conchuela

Leaffooted Bug

Leaffooted Bug

False Chinch Bug

False Chinch Bug

Monitoring: Accurately estimating numbers of panicle-feeding bugs per plant is affected by the tendency of these insects to congregate on sorghum panicles and within areas in a field. The beat-bucket technique described above for monitoring corn earworm can be used to estimate the average number of bugs per panicle. However, adult bugs will fly from the sampled plant and from the bucket. Plant leaves and weeds in the field also should be inspected for bugs. At least 30 plants from the whole field should be inspected to ensure reasonable reliability of sample estimates. Fields larger than 32 hectares should be subdivided for sampling into areas no larger than 32 hectares.
Management: Infestation in sorghum usually occurs when other hosts become unacceptable or unavailable. Early planting of sorghum helps avoid bugs migrating from other host plants. Not all species of stink bugs found in sorghum cause economic damage. Several species prey on harmful insects and, thus, are beneficial.
Sorghum kernels in the hard dough stage are usually not damaged by bugs. For most of the bug species, an infestation level per panicle of over sixteen bugs would be required to justify insecticide treatment at the hard dough stage of kernel development. The economic injury level for rice stink bugs ranges from four to nine and five to 13 at the milk and soft-dough stages, respectively. Insecticide applications would be justified when there are two to six or four to 11 per panicle at the milk and soft-dough stages of kernel develop, respectively, for southern green stink bugs, conchuela, or leaffooted bugs per panicle. The economic injury level for false chinch bug is 140 per panicle when infestations begin at the milk stage of kernel development.


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