Efficacy of Cotesia flavipes (Hymenoptera: Braconidae) in reducing Diatraea tabernella (Lepidoptera: Crambidae) injury in sugar cane

Sugar cane stem borers, Diatraea spp. (Lepidoptera: Crambidae), are the most important pests affecting sugar cane in Colombia. To date, the use of egg parasitoids such as Trichogramma exiguum Pinto & Platner (Hymenoptera: Trichogrammatidae), and larval parasitoids such as Billaea claripalpis Wulp and Lydella minense Townsend (Diptera: Tachinidae) have been the principal biological control approaches for pest management. However, a pest outbreak of Diatraea tabernella Dyar in the northern Cauca River Valley demonstrated that conventional control measures are insufficient, and that new pest control methods must be sought. Field evaluations were made using 2 sources of Cotesia flavipes Cameron (Hymenoptera: Braconidae): a commercial colony maintained in the laboratory, and a colony recovered from previous field releases (field-refreshed). Three releases of the parasitoid were made, each release consisting of 4 g of C. flavipes cocoons (about 4,000 wasps) per ha. The results from both sources of C. flavipes were compared with check plots where no releases were made. Larvae of D. tabernella were collected 2 different times (45 d and 75 d after the first release) and observed in laboratory. The proportion of larval parasitism ranged between 0.32 and 0.55, with no significant differences between sources of C. flavipes. Parasitism differed significantly from the check plots, where the proportion of larval parasitism was less than 0.1. Our results indicate that wasps from the check plots experienced an increase in the number of cocoons and wasps per parasitized larva between the first and the second larval collection. The high levels of parasitism in fields where C. flavipes was released resulted in a reduction of up to 65% in the percentage of bored internodes, demonstrating the potential of this natural enemy to effectively control D. tabernella. Changes in the number of progeny per parasitized larvae (cocoons and wasps) in the check plots can be explained as the increase of parasitoids in an area under the influence of nearby releases, and the subsequent effects of multiple parasitism. In addition, comparisons between the 2 parasitoid sources indicate higher biological efficiency in the field-refreshed plots expressed in an increase in adult longevity between the first and second collection times.