Antibioisis and antixenosis resistance to Dactylopius opuntiae (Hemiptera: Dactylopiidae) in Moroccan cactus germplasm
The wild cochineal, Dactylopius opuntiae (Cockerell), has become the main pest of the prickly pear [(Opuntia ficus-indica (L.) Miller] cactus crop in most of the Mediterranean countries, including Morocco since 2014. The use of D. opuntiae-resistant cactus ecotypes seems to be one of the most practical management option for the control of this pest. The objectives of this study were to identify the resistant genotypes and to determine the mechanism of resistance in 10 D. opuntiae-resistant cactus genotypes. From O. ficus-indica cochineal resistance screening experiments conducted in the laboratory and in mesh cages, 10 cactus genotypes that had fewer nymphs attached with no further developmental changes in the insect were identified. Studies on resistance mechanism showed that resistant genotypes of O. ficus-indica had significantly fewer D. opuntiae nymphs compared with susceptible genotypes. Genotypes 311 and 322 were the least preferred by D. opuntiae with 24.66 and 30 nymphs found after 72 h of infestation. All resistant genotypes have higher levels of dead nymphs compared with the susceptible control. The difference in the mean number of dead nymphs among the different genotypes tested and the control was highly significant. All nymphs produced on resistant genotypes died at first instar stage, indicating that these genotypes possess antibiosis as a mechanism of resistance. Genotype 295 had the highest number of dead nymphs, indicating a strong effect of antibiosis to D. opuntiae. Our study showed that both categories (antibiosis, antixenosis) play a role in resistance of the Moroccan cactus ecotypes.