Effect of potential companion crops on oviposition, development and infestation by diamondback moth, plutella xylostella (L.) on cabbage
Raini, Rebecca Kemunto
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The present study focused on laboratory and field evaluation of three brassica crops (Kale, Rape, Mustard) and three non-brassica crops (Cleome, Coriander and Onion) as potential companion crops in redacting the diamondback moth (DBM) population on cabbage. The effect of the crops on oviposition, development and the survival of DBM were assessed in the laboratory whereas infestation and damage were assessed in the field. Laboratory studies on oviposition by DBM moths showed that when cabbage is available for choice (under choice situation), more eggs were laid on mustard and rape, while very few eggs were laid on the non-brassica crops. Even when no other brassica hosts that were tested (80-108 eggs). Mustard appeared to attract the highest oviposition while onion recorded the lowest. Laboratory studies on the duration of development of larvae and pupae of DBM did not differ significantly among the brassica test host plants. The proportion of first instar larvae surving to adult stage in rape and Kale 927.0-29.5%) was comparable to that on cabbage (31%), while mustard appeared less suitable (21.5%) and was close to cleome (21.0%). Onion and coriander did not permit the first instar larvae to survive even into second instar stage. The adults that emerged from the DBM larvae fed on different test hosts did not show any significant differences in their longevity. However, the fecundity was significantly lower (3.6 eggs/ adult) among the adults reared from cleome and this was significantly different from the other test brassica hosts, namely Kale (114.9 eggs), rape (71.8 eggs) and mustard (45.8 eggs) and cabbage (115.6 eggs). There was no significant difference among the test brassica hosts. In the field studies where plots of cabbage were planted with and without the six test plants as companion crops, the DBM larval infestation was significantly low in plots intercropped with coriander (1.35 larvae per cabbage plant), and cleome (1.67 larvae per cabbage plant). Cabbage plots intercropped with the three brassica test crops: Mustard, Kale and rape also recorded significantly low infestation was also found to be significantly reduced by all the companion crops, compared to unprotected cabbage monocrop plot. The results have indicated the overall potential of brassica crops (like mustard) to be utilised as a trap (pull) crop and non-brassica crops (like coriander) and cleome as repulsive (push) crops in reducing the oviposition, survival and crop damage by DBM on cabbage. Nevertheless, there is need to further evaluate the optimum proportion and planting pattern of the promising push-pull crops and their relative economic as well as ecological benefit to the cabbage agro ecosystems.
- MST-Zoological Sciences