Bean Bugs

Pests of Field Crops in Southern Africa

BEAN BUGS

(Hemiptera/Heteroptera: Coreidae)

Þ

Þ

Þ

Þ

Þ

Text Box: The coreid bug, Clavigralla tomentosicollis, can be troublesome on many bean species. It is a slender, spiny brown bug of about 10 mm in length, and the stiff piercing “beak” can be seen lying between the forelegs along the ventral surface of the body. It has a “shy” nature, remaining within the canopy and hiding when disturbed. It should not be confused with the similar, but much bigger and more heavily armoured “tipwilters”, which belong to the same family, and which tend to damage the plant by causing growing points to wither and die when pierced. TOP

Text Box: The main host plants are beans of the Phaseolus genus, although other legumes and pulse crops, such as soyabeans, are also attacked. TOP

Text Box: The damage is caused when the bugs pierce the developing seeds in the pods, with the result that the beans may be dimpled, blotched or even shrivelled. It is thought that these symptoms may be partly due to infection by a fungus, Nematospora coryli. If the bean crop is to be grown for seed, the resulting germination ability of the crop is often impaired. One often finds that the latest-maturing bean crop is by far the most damaged by these bugs, as if they find themselves congregating on the last green plant material of the season. This is definitely the case in soyabean crops. When the population of the bugs is high, a considerable amount of damage can be caused to seed number, seed weight and seed quality. TOP

Text Box: Eggs are laid in clusters on the foliage and after about a week hatch into tiny first instar nymphs. They pass through five nymphal stages in about a month, gradually growing the wings, but otherwise similar to the adults in appearance. TOP

Text Box: There have never been any specific control measures registered for bean bugs, probably because they are sporadic pests. They are difficult to spray, however, because they are very mobile and move away when there is any disturbance in the crop. Reasonable control may be achieved with sprays of relatively short-lived organophosphates such as trichlorfon, but any control measure should take into account the harvest interval, particularly in the case of beans harvested for vegetables. TOP

Bean bug.

Bean bug eggs.

Bean bugs feeding.

Dimpling caused by bean bug.