Population Maintenance Of Liriomyza Sativa In Laboratory And The Odor Learning In Its Parasitoid

Liriomyza sativae, the vegetable leafminer, has been an important insect pest of vegetables and ornamentals, since it was introduced in China in1990’s. However, this insect species has been becoming a model insect to study on the plant-insect interaction, cold tolerance, and host adaptation.The process of parasitoid searching the host insect is divided into four main steps: the host habitat location, host location, host acceptance and host regulator. Our group has demonstrated that the leafminer-induced plant volatiles played important role in the host habitat location. Obviously, the hidden living lifestyle of larvae is beneficial for Liriomyza sativae to avoid being found out by parasitoids directly via vision after the host habitat location. Therefore, which cues are more detectable and reliable is a vital question for the approaching parasitoid. Based on our previous study, we hypothesized that Opius dissitus may locate the larvae of Liriomyza sativae through larvae-associated odors accurately. The larvae frass was postulated as this kind of odor sources for it possesses the characteristic of detectability and reliability of the presence of living larvae on the host plants. Besides, To facilitate the population maintenance in laboratory, we studied the effect of cold storage on the pupal development and survivorship at8℃, which is the developmental threshold of L. sativae. Then, this paper is divided into two parts:1) Three-day pupae of L.sativae were collected and stored at8℃. The effect of time courses (0day,7days,14days,21days,28days,35days) of cold storage on the development and survivorship of the vegetable leafminer were studied. The morphology of developmental pupae was observed by dissection in a24h interval. The pupae of L.sativae were defined to different development stages according to their morphology. In order to know the reason of mortality, we dissected and compared the dead pupa of each treatment based on the definition of the pupal stages. we found that eclosion rates decreased following the time courses of cold storage. Emergence rate was significantly affected after14days, and dropped to zero at day35. The developmental stage of pupa were divided into7stages:prepupal stage, crypto cephalic stage, early phanerocephalic stage, yellow-eyed stage, amber stage, red-eyed stage, and bristle stage. We found that the dead pupa were mostly presented at bristle stage, and the percentage of dead pupa increased with the time of cold storage. The optimized cold storage time for pupa is within14days at8℃in the laboratory and the bristle stage is the most sensitive stage to cold temperature.2) Based on the studies of the tritrophic interactions among plant, leafminer, and parasitic wasp in our laboratory, we conducted the behavioral observations of parasitoids and chemical analysis relative to larvae frass of leafminers. The mated female Opius dissitus have been divided into two groups:experienced parasitoid and naive parasitoid. The behavioral study showed that64%of experienced parasitoids can locate larvae leafminers and complete the oviposition within2hours, but only16%of naive parasitoid can do so, indicating that odor learning played important role in the host location of parasitoid. Then, we extracted the chemical compounds of L.sativa frass, which was collected from3-day larva tunnels. The following behavioral observation showed that63%of experienced parasitoids were chemotactic to extraction of larval frass, but only23%of experienced parasitoids displayed the same preference for solvent control. Our GC-MS study on the odors from healthy bean leaves and larval frass revealed that7specific compounds merely detected in the fecal crude extractions, among which pentadecanal is the most abundant component in the blend. Our further GC-EAD study confirmed that four specific compounds of the seven elicited the obvious electrophysiological responses on the antennae of parasitoids and pentadecanal was the most significant ones. Using the synthetic pentadecanal, we found that experienced parasitoids approach this odor source more often than the naive parasitoids. Therefore, our study demonstrated for the first time that through the learning of the larvae-associated odor, at least in part the compound pentadecanal, leafminer parasitoids locate the host larvae more efficiently and accurately.