Parasitism and Development ofConura acuta(Hymenoptera: Chalcididae) on Sugarcane Stalkborers (Lepidoptera: Crambidae) in Mexico

Abstract

A 10-yr study was conducted in the Los Mochis sugarcane area in western Mexico to determine rates of parasitism by Conura acuta (F.), an indigenous pupal parasitoid of the stalkborers Diatraea considerata Heinrich and D. grandiosella Dyar. Parasitism by C. acuta was practically zero in 1993, progressively increased soon after chemical insecticide applications were discontinued in the sugarcane area, peaked at a yearly average of 3.2% in 1997, and stabilized thereafter at 2–3%, except in 2000 and 2002, probably because of drought. Seasonal parasitism by C. acuta was density-dependent, with maximum parasitism occurring during summer, when hosts were more abundant. Maximum parasitism by C. acuta occurred during mid-September 1996 with 43.3%. Although parasitism by C. acuta was generally low throughout the study, its impact may be important in terms of indispensable mortality, late in the life history of stalkborers. No field parasitism by C. acuta was observed on Eoreuma loftini (Dyar), a concurrent sugarcane stalkborer in this area. In the laboratory, the most preferred hosts by C. acuta were D. grandiosella and D. considerata with 60% parasitism, whereas E. loftini, D. saccharalis (F.), and Spodoptera frugiperda (J. E. Smith) were poorly accepted (<5%). Parasitism was highest in the youngest pupae (1 d old) and decreased progressively with host age. Late-instar larvae and prepupae were not accepted, showing that C. acuta is a true pupal parasitoid (idiobiont). Attraction and parasitism by C. acuta were higher when pupae were exposed with larval frass compared with clean pupae, suggesting the presence of a kairomone in the process of host finding and acceptance. Developmental time of C. acuta was 10 d longer on D. considerata than on D. grandiosella, with no difference between parasitoid sexes within hosts. In contrast, C. acuta longevity did not differ after emerging from either host species, with females living >20 d longer than males. Opportunities for using C. acuta, the only known pupal parasitoid of sugarcane stalkborers in Mexico, as a biological control agent are discussed.