Relationship of sitona discoideus (coleoptera: curculionidae) larval density to september-october potential soil moisture deficits

Abstract

The relationship between maximum potential soil moisture deficit (D max.) during Silona discoideus Gyllenhal oviposition and subsequent peak larval establishment in young lucerne (Medicago sativa L.) is described. Regression analysis showed that variation in larval establish-. ment from year to year was best correlated with the values of D max. attained during September and October. The best fit was hyperbolic, implying a precipitous reduction in peak larval numbers when D max. exceeded about 50 mm. After this reduction. larval populations were stable at about 1000/m2. This pattern is probably a result of rhizobial nodule availability for neonate larval populations. The eventual size of larval populations is related to the prevailing soil moisture conditions in September-October. This period has previously been found to be the most important for sitona weevil egg-laying within New Zealand, in terms of resultant larval establishment. © 1986 Taylor & Francis Group, LLC.