In southern provinces, particularly Cautín, "white grubs" (Scarabaeid larvae) do damage to cereal and forage crops to a value no less than 60 millions of Chilean pesos per year.
1.- Observations accomplished from 1948 to date permit afirmation that there are six species of Scarabaeids more or less harmful including one new species undescribed yet. This paper deals especially with the Ruteline Hylamorpha elegans Burm. of which several ecological aspects, geographical distribution, population density and host plants are studied.
2.- Prunus avium L. is mentioned as a new ocasional host plant for the adult stage of this insect.
3.- A demographic variation reached its peak in 1946 and 1947 declining thereafter to its normal level of 10 to 25 larvae per square meter, which has been maintained to the present.
4.- The density of larval population increased up to 200 and even 300 individuals per square meter during the acute period of attack in 1946-47.
5.- The life cycle of Hylamorpha elegans takes only one year.
6.- Often the species Phytoloema hermanni Germ., Sericoides germanini D. T. and Schizochelus breviventris Phil. and rarely Brachysternus prasinus Guér. live in the same biotopes as Hylamorpha elegans (Burm.)
7.- Larva activity of "Sanjuan verde" takes place in the soil at a depth of no more than 20 cms. During the winter (especially June and July but even in August) they come very close te the soil surface and destroy plants roots.
8.- From the study of the feeding habits of Hylamorpha elegans a list has been prepared of plants that are associated in differenf combinations in infested areas of Cautín province.