RELATIONSHIPS BETWEEN THE PARASITOIDHYPOSOTER EXIGUAEAND THE CABBAGE LOOPER,TRICHOPLUSIA NI: EFFECTS ON HEAD-CAPSULE WIDTH, LIVE AND DRY WEIGHTS, AND HEMOLYMPH SPECIFIC GRAVITY OF HOSTS AT DIFFERENT AGES

Abstract

AbstractThe effects of parasitism byHyposoter exiguae(Viereck) on certain developmental parameters ofTrichoplusia ni(Hübner) were influenced by host age at parasitism.Head-capsule growth increments for parasitizedTrichoplusia nibecame smaller with each successive molt during parasitism so that determination of instar on the basis of head-capsule width became impossible.ParisitizedT.nishowed a proportionately smaller gain in weight from time of stinging until parasitoid emergence the older they were when stung (6 times for 3rd instars; 2 times for 4th instars; and no gain for 5th instars). This retardation was evident 24 h after parasitism. Essentially the same results were obtained for dry weight.Percentage dry weight of parasitized larvae tended to increase over control values until the 5th stadium when controls abruptly increased. Values for parasitized 5ths remained below the controls. Values found on the last days reflected those of the parasitoid which composed most of the mass inside the host cuticle.Hemolymph specific gravity in controls and parasitized 3rd instars oscillated with a frequency of one stadium in the 3rd, 4th, and early 5th stadia. Specific gravity of controls then rose to a maximum of 1.0501 in the prespinning phase and dropped by the pharate–pupal phase. Values for parasitized larvae in the 5th stadium rose slightly before leveling off, and parasitized 5th instars rose to a maximum on the next-to-last day. Maximum values attained for hosts parasitized as 3rd and 5th instars never reached that for controls on day 11. This may be related to the complete unacceptability or unsuitability ofT.nilarvae for parasitism from day 11 on.