Abstract
The distribution and mor phology of various sensory organs (sensilla) on the antenna and mouthparts of Spodoptera littoralis larvae were investigated using scanning electron microscopy. In this study we focused on the morphological alterations of the antennal and mouthparts sensilla of Spodoptera littoralis last instar larvae reared on different hos t plants; alfalfa, cotton, and soybean leaves. Based on our results, we found that sensillum chaeticum on the antenna was morphologically affected by shifting the host plan t since it became longer in those larvae reared on soybean and alfalfa leaves when compared with those reared on cotton leaves. Furthermore, several morphological variations were observed in sensilla trichodea on the labium, mandibles, and labrum by shifting the host plant. In addition, clear morphological changes were observed in sensillum digitiformium on the maxillary palps due to changing the host plant. On the other hand, no morphological changes in ante nnal basiconic, trichodium and styloconic galeal sensilla styloconica, maxillary campaniform and placodeum sensilla were observed. Taken together, these results showed that shifting host plants of Spodoptera littoralis larvae induced plasticity and morphological changes of th e antennal and mouthparts sensilla.
Highlights
Insects have a special need to have developed sensory organs to monitor their external environment (Zacharuk, 1985)
We found that, changing the provided food items and rearing of Spodoptera littoralis larvae on different host plants induced distinct changes and plasticity in the antennal and mouthparts sensilla
Our results showed that feeding of Spodoptera littoralis larvae on different host plants affected size and morphology of some antennal and mouthparts sensilla such as antennal sensillum chaeticum (SCh), labial sensillum trichodium (STr), mandible (Tr) and labrum (T1-T6) sensilla trichodea, and maxillary palps sensillum digitiform (SD)
Summary
Insects have a special need to have developed sensory organs to monitor their external environment (Zacharuk, 1985). Larvae are generally restricted in habitat and mobility, and are generally more favored targets for the management and control of pest-insect populations (Zacharuk and Shields, 1991). Knowledge of the sensory organs involved in their food-finding, feeding behavior, and ingestion is paramount in the development and application of those pest control agents, in particular, that require ingestion (i.e. microbial agents) or that will prevent feeding (antifeedants), Azza A. Taste and tactile cues for food selection and gustation are of primary importance to the immature stage, along with sensilla that provide temperature, humidity, tactile, and some visual monitoring for orientation and protection (Zacharuk and Shields, 1991). Immature stages develop through several molts, at which times cuticular parts of existing sensilla are replaced and new sensilla may develop (Zacharuk and Shields, 1991)
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