Implications of sex and ovarian status on the responses of Luclia sericata (Meigan) (Diptera: Calliphoridae) to volatile compounds related to carrion

Dimethyl Disulfide (DMDS) is a known Volatile Organic Compound (VOC), which is one of the prominent sulfur VOCs emitted by decaying vertebrates. Proteus and Providencia species, which are commonly associated with blow fly larvae and adults, are able to deaminate, demethiolate and oxidate methionine to produce DMDS, linking microbes to fly colonization through VOC production. In the case of vertebrate carrion ecology, blow flies, such as Lucilia sericata (Meigan) (Diptera: Calliphoridae), are typically the first arthropods to colonize carrion. Consequently, these insects have been selected to have highly sensitive olfactory systems enabling them to detect low levels of VOCs indicative of the presence of carrion sources. It is suspected that DMDS might be a key VOC utilized to direct/locate food or oviposition sites. The behavioral responses of 7-9-day-old L. sericata adults to DMDS at dose of 10 µg, 0.25 µg, 0.05 µg, 0.005 µg, 0.0005 µg were examined in a Y-tube olfactometer. Twenty non-gravid, gravid females and males were tested for each dose. Individual flies were introduced into a Y-tube and the residence time in each arm corresponding to a treatment recorded. Logistic regression was used to analyze the behavioral data taking into account dose, sex and ovarian development on the response of the flies. Behavioral responses to DMDS were variable by different doses. DMDS was repulsive for gravid females while  marginally attractive for males at 0.005 µg. DMDS was also marginal attractive to males at 10 µg. Sex was significance in explaining the choice fly made in the bioassay in response to DMDS at dose 0.005 µg and 0.05 µg. Previous research determined DMDS was attractive for female flies at the dose of 0.05 µg; however they did not distinguish between gravid and non-gravid females. Failure to take into account ovarian status of the tested females would likely result in discrepancies in conclusions drawn regarding the attraction of female flies to a compound or carrion source. These data presented in the current study demonstrate a relationship between sex and physiological state with regards to attraction to a VOC that occurs during decomposition. Understanding this relationship could provide insight to the mechanisms regulating subsequent colonization and arthropod succession; clarifying previous work with this compound regarding the timing of attraction of different phenotypes (male, non-gravid and gravid females) to remains.