Comparative Study On Ovipositor Sensilla Of Insects With Four Different Types Of Oviposition Strategies

Oviposition process of insects is one of the most important steps of their lifecycle history, certain insect species overwinter in their stage of egg, and the newly hatched larvae tend to be immobile or slow in movement, therefore, it is essential that the female provide the egg with suitable environment as well as relatively sufficient protection, most of all, make sure that their offspring can have access to enough source of food to finish their larval stage. Four stages concerning the site location of insect oviposition are concluded: host orientation, landing, assessment and acceptance or rejection of oviposition. During this process, the antenna, maxillary palp, labial palp, tarsi, leg and ovipositor are the most vital sensory apparatus functioned in the location and external assessment of host. The insect ovipositor, as the one apparatus directly used in this process, plays a vital role in monitoring the micro-environment of the oviposition site and triggering the final oviposition decision. In this study, we reveal and conclude the ovipositor morphology and ovipositor sensilla on insects of economic values in China, associated with profound discussion of their oviposition behavior, it enables us to have a better understanding of the stimuli sensory mechanism, and furthermore, the communication between insects and plants. This study provides us with fundamental knowledge about ovipositor sensilla, leading to promising further electrophysiology and electrochemistry research.In this study, ovipositor morphology and sensilla morphology, distribution as well as ultrastructure is revealed, in the meantime, via indoor observation of oviposition behavior and studies regarding oviposition behaviors, four different strategies of oviposition are concluded, i.e., direct external oviposition, scar carving oviposition, crack detecting oviposition and host penetration oviposition. Morphology, density and distribution of ovipositor sensilla in different oviposition strategies are compared and discussed for detailed functions, some of the main results are listed as below:1. Insects of direct external oviposition behavior have short ovipositors on which sensilla with two distinct types are distributed. These sensilla chaetica could be used to evaluating the superficial conditions, chaetica hairs could also be used to sensing the air current or vibrations as well as monitoring the location of eggs.2. Weevils with scar carving oviposition strategy have ovipositor characterized as extensible tubes, sensilla chaetica with distinct variation in lengths as well as sensilla basiconica are discovered on their ovipositors. Chaetica sensilla could be used in pushing the eggs into the oviposition scars, basiconica sensilla proves the existence of chemical communication between weevil and host.3. One weevil and three carpenter moths are cataloged as cracks detecting oviposition type. Sensilla basiconica are found on all their ovipositors, while sensilla trichodea are discovered on the ovipositors of carpenter moths. The various chemical sensitive sensilla found on this type of oviposition prove that these insect could be receiving and evaluating a lot of both chemical and mechanical cues from the hosts.4. Ovipositors of the host penetration oviposition type have generalized ovipositor with all or part of the primary valvula structures preserved. Sensilla on these valvulae are sensory pits with or without a terminal pore. These pits functioned in evaluating the inner status of the host and lead to a decision of oviposition.5. The comparison of ovipositor and ovipositor sensilla morphology among insects demonstrating these four different modes of oviposition revealed that ovipositor and sensilla typology, distribution are distinctively different, while within the same mode of oviposition, different insects shared a lot of similarities.