Common Potato Pksts. T 



TnE Potato Ladybird Beetle (Ejrilachna clregei Mills.)- 



Many ladybirds are valuable friends of the farmer, since they 

 render assistance in the control oE such important pests as scale insects 

 and plant-lice. The present species is, however, a plant-feeder found 

 all over the Union and in Rhodesia. It causes daniag'e to various 

 crops, both the adult and larvae feeding on the foliage of the potato, 

 pumpkin. vepetal)le marrow, cucumber, turnip, radish, melon, bean. 

 })arsnip, spinacli, and wild solanaceous plants; the potato is its 

 favourite food-plant. 



The presence of this insect in a potato-field is readily determined 

 by finding" the spiny yellowish larvae or the adult beetles on the 

 foliage. The adult is oval and strongly convex in form, each wing- 

 cover having 8 or sometimes 10 buff spots. The ground-colour of the 

 wing-covers is black, the iegs and the ventral slch* of the body being- 

 buff. 



Life-history. — The female deposits from 75 to 110 yellow eggs in 

 three or four clusters on the under surface of the leaves. After 

 7 to 11 days the yellow larvae hatch out {\i the atmospliere contains 

 much moisture many eggs do not hatch) and are at first very incon- 

 spicuous and gregarious in their habits. They are provided with long 

 branched spines which are white immediately after hatching, but soon 

 become darker. After the first moult, which occurs 10 to 14 days 

 after hatching, the laiwae scatter over the plants ; they feed on the 

 lower epidermis of the leaves, wliereas the adults usually feed on the 

 upper. 



xlfter the lapse of 28 to 36 days the larvae are full grown and 

 ready to puj)ate. For this purpose they seek sheltered spots on the 

 food-plants, and, hanging themselves by the tail-end to a leaf, twig, 

 or other convenient place, transform ijito yellow pupae. After 6 to 10 

 days the adults emerge from the pupal sheath. s. The complete life- 

 cycle takes on an average 49 days, and there are two generations in a 

 year. During the winter the beetles hibernate under the bark of euca- 

 lyptus trees, stones and rubbish near gardens, and potato fields. 



Control. — Both larvae and adults are comparatively easy to con- 

 trol because of their sluggish habits and the tendency whicli they 

 have to remain on particular leaves until these are entirely skele- 

 tonized. 



It is essential that spraying be resorted to as soon as the larvae 

 have been observed on potato foliage, for in the early stages the young 

 are very gregarious, and hence more easily destroyed than later, wiien 

 they have scattered over the plants. 



Use arsenate of lead at a strength of 3 lb. of the paste or 1^ lb. 

 of the powder for every 50 gallons of water, and endeavour to cover 

 both the upper and lower surfaces of the leaves with the spray. 

 Instead of lead arsenate paris green could be used in the proportion 

 of 1 lb. to 100 g-alJons of water, to which 2 lb. of slaked lime are 

 added in order to neutralize any soluble arsenic which may he 

 present, 



TAterature. — " Two Ladybirds injurious to Potato Plants," by 

 P. -Tack, Bull. 158. Salisl)nrv, Phodesia. 



