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Chemical cues that Bracon compressitarsis Wharton and Bracon thurberiphagae Muesebeck (Hymenoptera:Braconidae) utilize to localize their host Anthonomus grandis Boheman (Coleoptera:curculionidae)
We conducted studies to identify and characterize chemicals responsible for host habitat location by B. compressitarsis and B. thurberiphagae. Copaene, caryophyllene, and humulene were responsible for the orientation of B. compressitarsis to the host plant (Hampea spp. male plants). Caryophyllene and chemicals from weevil frass were responsible for the orientation of B. thurberiphagae to its host plant (Gossypium thurberi). Bracon compressitarsis and B. thurberiphagae were unable to recognize G. hirsutum as host plant to search for boll weevil because of the difference in the ratios and concentrations of plant chemicals when compared against the native host plants, H. nutricia and G. thurberi, respectively. Females of both Bracon species responded to chemical cues after the preovipositional period. Bracon compressitarsis preovipositional period lasted 3.0 ([plus or minus]0.9) days, male and female longevity was 30.1 ([plus or minus]4.5) days and 63.3 ([plus or minus]7.7) days at 23 [plus or minus] 1°C. The preferred weevil instar used as host was third instar. Bracon thurberiphagae preovipositional period lasted 3.04 ([plus or minus]0.5) days, male and female longevity was 28.0 ([plus or minus]5.2) days and 60.5 ([plus or minus]6.3) days at 23 [plus or minus] 1°C. The preferred weevil instar used as host was third instar. These ectoparasitoids were gregarious developing a mean of 4.6 ([plus or minus]3.0) parasitoids per host larva. Both species host fed preferentially on the hemolymph of third instars during the preovipositional period through a feeding tube constructed by the female. Hosts which were used for feeding were not parasitized and they did not complete development. Heliothis virescens was tested as an alternate host for the rearing of B. thurberiphagae. After 3 generations of rearing this ectoparasitoid on H. virescens, the colony of B. thurberiphagae had a severe reduction in fecundity. After the addition of amino acids to the adult wasp diet, a 100% improvement in fecundity of this colony was observed. Analysis of gossypol and carbohydrate contents of the native host plants and cotton indicated that gossypol content in leaves and buds of G. thurberi was significantly higher than of G. hirsutum and both Hampea species. The content of gossypol in H. nutricia leaves was significantly higher than in H. trilobata leaves. However, the gossypol content in the buds of these two Hampea species was similar...