Dactylopius opuntiae: control by the Fusarium incarnatum-equiseti species complex and confirmation of mortality by DNA fingerprinting

Cultivation of the prickly pear cactus, Opuntia ficus-indica, an important cattle food in the semiarid region of Brazil, has been increasingly compromised by predation by the cochineal scale Dactylopius opuntiae. Entomopathogenic fungi represent a low environmental impact alternative to controlling this insect pest, and the genus Fusarium has been described as a promising agent for that task. As such, we selected isolates of the Fusarium incarnatum-equiseti species complex (FIESC) to evaluate their potential biological control of D. opuntiae and confirmed their efficiency/presence in the field through morphological and molecular characteristics. The pathogenicities of 25 isolates of FIESC obtained from D. opuntiae were evaluated. The isolates URM6782, URM6778, and URM6811 demonstrated kill rates above 45%, and good sporulation characteristics, and were thus selected for field testing. The isolate URM6782 showed the highest kill rate in the field, and amplification profiles obtained using the ISSR UBC834 marker confirmed that the isolates released in the field were in fact the causal agents of the high mortality of D. opuntiae. We also observed natural biological control by native Fusarium species present in the field. Our results suggest that the isolates URM6782 and URM6778 show significant promise for controlling D. opuntiae and that the ISSR primer UBC834 can be used to monitor those isolates when released into the field. This work represents an initial study directed toward the biological control of D. opuntiae using novel isolates from the FIESC.