ENDOGENOUS REGULATION OF MOSQUITO HOST-SEEKING BEHAVIOR BY A NEUROPEPTIDE

Most species of mosquitoes must engage in host-seeking behavior to fin d a vertebrate host and ingest a meal of blood in order to initiate an d complete each oogenic cycle. Female Aedes aegypti fed to repletion a lmost immediately fail to respond to odor cues that would otherwise le ad them to a host for another blood meal. This response is delayed for approx. 24 h in females that ingest small blood meals. In both instan ces, during this period of inhibition, the hemolymph titer of Ae. aegy pti Head Peptide I (Aea-HP-I; pGlu-Arg-Pro-Hyp-Ser-Leu-Lys-Thr-Arg-Phe -NH2) rises to a peak, as measured with an Aea-HP-I radioimmunoassay ( RIA). This homologous RIA is based on an antiserum that specifically b inds Aea-HP-I (5-100 fmol range, 1:100,000 final dilution) as compared to other related peptides. Aea-HP-I and at least one other immunoreac tive peptide were identified in pooled hemolymph from sugar-fed female s with HPLC fractionation and the RIA. To determine whether Aea-HP-I a ffects host-seeking behavior, synthetic Aea-HP-I and related peptides were injected into non-oogenic females, which actively seek a host. Ho st-seeking behavior was inhibited by Aea-HP-I within a dosage range of 16.5-825 pmol/female, whereas related peptides differing by a few ami no acids had no effect. The relatively high doses of Aea-HP-I, which e licited behavioral inhibition, were rapidly degraded in vivo as determ ined with the RIA of hemolymph from experimental females. Other associ ated behaviors were not altered by the Aea-HP-I injection, even at hig h doses. These results together suggest that Aea-HP-I regulates the ob served behavioral inhibition in this mosquito species.