Host resistance to two parasitoids (Diptera: Tachinidae) helps explain a regional outbreak of novel Diatraea spp. stem borers (Lepidoptera: Crambidae) in Colombia sugarcane

Lydella minense and Billaea claripalpis (Diptera: Tachinidae) are important parasitoids used in augmentation biological control of sugarcane stem borers, Diatraea spp. (Lepidoptera: Crambidae), the primary pests of sugarcane in Colombia. Following the recent discovery of two new Diatraea species in the Cauca River Valley (CRV), D. tabernella and D. busckella, stalk-boring damage to sugarcane has increased and rates of larval parasitism have declined. The present study assessed the suitability of all four stalk-boring Diatraea species now present in the CRV, D. tabernella, D. busckella, D. indigenella and D. saccharalis, as hosts for the two parasitoids. Following manual inoculation of larvae with maggots of L. minense and B. claripalpis, the development, immature survival, sex ratio and longevity of resulting flies were recorded. Both parasitoid species parasitized a lower percentage of D. tabernella and D. busckella larvae compared to larvae of D. saccharalis or D. indigenella. Although host larvae were more likely to yield two puparia of L. minense than of B. claripalpis, the likelihood of a second puparium was reduced when L. minense parasitized D. tabernella and D. busckella. These results suggest these two Diatraea species have resistance to parasitism by the tachinids, which might explain why outbreaks of these pests have occurred in the regions of the CRV where commercial releases of the parasitoids are relied upon as the primary pest management tactic. Although breeding programs may eventually provide flies with improved ability to parasitize these novel host species, additional work is warranted to explore alternative pest management tactics for these stem borers.