Comparative studies of two closely related Spodoptera species (Lepidoptera: Noctuidae) on six selected host plants under laboratory conditions

Abstract

Series laboratory trials were conducted to evaluate some biological characteristics of Spodoptera frugiperda (FAW) and Spodoptera littoralis (CLW) on various selected host plants under different conditions. Under no-choice conditions, parsley appeared to be the most preferred host for the larvae of both insect species, with the shortest larval stage for FAW compared to pepper, which was the least suitable; while the shortest larval stage for CLW was observed on castor, with the highest survival rates, and the longest on maize, with the lowest survival rates, making it the least suitable host for the insect; and the highest survival rates for S. frugiperda larvae were observed when fed on maize and the lowest when fed on watercress. Under binary choice conditions with castor, castor was the preferred host for the larvae of both species compared to other host plants offered as a second choice, with the exception of parsley, which was preferred by FAW larvae over castor, compared to pepper, which was the least preferred; whereas maize was the least preferred host for CLW larvae compared to other available host plants in binary treatments, which seemed similar larval consumption rates; and the shortest larval stage for S. frugiperda was observed in the binary treatment combined castor and maize, while the highest larval survival rates were recorded in the binary treatment combined castor and parsley compared to the binary treatment combined castor and watercress, which showed the lowest larval survival rates; meanwhile the longest larval stage for S. littoralis was observed in the binary treatment combined castor and maize, along with the lowest larval survival rates. However, under the conditions of binary choice with presence of maize, parsley appeared to be more preferred than maize in this combined treatment, while maize was the most preferred host plant of S. frugiperda larvae compared to other host plants available as a second choice among other treatments, and pepper remained the least preferred by the larvae. On the other hand, maize was the least preferred host for S. littoralis larvae compared to other available host plants in all binary treatments; the highest survival rates of S. frugiperda larvae was found in the treatment combined maize and parsley, on the contrary of S. littoralis; and the larval duration of CLW in all binary treatments was varied in the presence of maize; meanwhile the longest larval period for S. frugiperda was observed in the treatment combined maize with pepper. Castor, followed by parsley, were the most preferred hosts for the larvae of both species under multi -choice conditions, compared to other host plants which were combined with them; and the duration of FAW larvae was shorter than S. littoralis, which was lower in survival rates of larvae compared to S. frugiperda. Furthermore, larval growth indexes of S. frugiperda and S. littoralis were affected by the host plant species; where the highest growth index of S. frugiperda was obtained when it was fed on maize leaves; while, the lowest was recorded on watercress and pepper leaves. For S. littoralis, the highest growth index was obtained when it was fed on castor leaves; while, the lowest was recorded on maize leaves.