The effect of different host plants on the reproduction and longevity ofNysius natalensis

Abstract

AbstractNysius natalensisEvans (Hemiptera:Orsillidae) is a pest of sunflower inSouthAfrica. Adults invade sunflower fields from their weedy hosts which occur inside crop fields and on surrounding headlands. The host plant suitability for survival and reproduction as well as the effect of within‐generation host switching was studied on different wild host plants and sunflower. Life history parameters used to assess host plant suitability were F1adult survival, pre‐oviposition period, fecundity, and longevity. Nymphs and adults were provided with stems and seeds of five host plants, viz.,Amaranthus hybridusL. (Amaranthaceae),Portulaca oleraceaL. (Portulacaceae),Chenopodium albumL. (Chenopodiaceae),Conyza albidaSpreng. (Asteraceae), and sunflower,Helianthus annuusL. (Asteraceae). Nymphs were reared on crushed seed of the five plant species. After completion of the nymphal stage, emerging adults of each host plant group were provided with seed of a different host plant species for food. Adults did not survive long on stems only and very few eggs were laid. Seeds of the host plant species were shown to be an essential source of nutrients forN.natalensisreproduction, whereas the vegetative plant parts were unsuitable. Nymphal food and host‐plant switching between the nymphal and adult stages significantly affected the pre‐oviposition period. Nymphal and adult food source also affected female longevity. The number of eggs laid was not influenced by nymphal food, but was influenced by adult food and the switch between nymphal and adult food. The comparative attractiveness of sunflower and wild host plants for oviposition was also investigated and showed that females preferred to lay eggs on wild host plants, compared with sunflower. These results may explain whyN. natalensiswill lay their eggs on sunflower after weeds in the vicinity are controlled, or senesce toward the end of the growing season.