Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 1995
Publication Date: N/A
Interpretive Summary: To evaluate effectiveness of various vaccine formulations for cattle grub control, calves are infested with cattle grubs and the larvae closely observed. Previously, when cattle grub larvae arrived in the back tissues of cattle, the location was mapped, then a gown glued to the cow's back so that the larvae emerging from the back could be collected. Emerged larvae represented the potential adult flies that could reinfest the herd. It is important in evaluating effectiveness of vaccination to know exact where, in the host, larval death occurs and its total extent. Certain problems with the gowning included prevention of "mapping" and adverse effects of gown or glue on younger larvae. The present study was designed to provide biological data to support a new technique for larval collection. Mature 3rd instars are now collected just before pupation. Developmental aging of 3rd instars was followed by observation of the breathing apparatus of the larva while still in the cow's back tissues. Grub larvae molt to 3rd instar within 30 days of arriving in the back. Larvae emerge from the back in 60 days. A larva surviving to molt to 3rd instar has 86.7% chance of survival. A larva surviving to the development stage that is presently harvested has 93.3% chance of emergence. These data allow us to age-grade larvae in the backs of cattle and to support our technique of collection.
Technical Abstract: ABSTRACT Hypoderma lineatum (Villers), the common cattle grub, is an insect parasite that resides in a warble, in the subcutaneous tissues of the backs of cattle during a portion of the life-cycle. In the warble the larva undergoes two molts to the third-instar. In this study the development of the posterior spiracular plates of the third-instar larva of H. lineatum was observed in situ. Larvae were observed to molt to the third-instar, Phase 1 (P1) stage of development, 28.6 (+/-3.9) days after digesting a breathing hole in the backs of previously uninfested calves. The development of the spiracular plates through the various recognizable stages occurred on a 5- to 6- day period. It took 54.2 (+/-5.1) days for third-instar larvae to develop to the Phase 3 (P3) stage, the stage prior to larval emergence from the host and pupariation. The average elapsed time from the third-instar P3 stage to emergence from the host was 5.5 (+/-2.9) days. Of 22 larvae that were followed from arrival in the back to pupariation the elapsed time was 59.4 (+/-6.1) days. Most larval mortality in the back occurred during the first and second-instar stage. Of larvae surviving to the third-instar, 86.7% successfully emerged from the host. Of third-instar larvae surviving to the Phase 2 (P2) "goldplate" or P3 stage, 93.3% successfully emerged from the host.