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ARS Home » Plains Area » Kerrville, Texas » Knipling-Bushland U.S. Livestock Insects Research Laboratory » LAPRU » Research » Publications at this Location » Publication #350375
Title: Cluster size influence on the survivability of Rhipicephalus Boophilus microplus larvae under low relative humidity stress

Author
item ZAMORA, EMILY - University Of Texas Rio Grande Valley
item LEAL, BRENDA - University Of Texas Rio Grande Valley
item DEARTH, ROBERT - University Of Texas Rio Grande Valley
item Thomas, Donald

Submitted to: Entomological Society of America, Southwestern and Southeastern Branch
Publication Type: Other
Publication Acceptance Date: 3/25/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Seed cattle ticks (immature ticks) are known to be more numerous in the rainy season because they are very susceptible to dessication in the dry periods. Cattle ticks at this stage are known to cluster into balls and it is thought that this reduces their moisture loss and enables them to survive longer during droughts. To test this theory we placed different numbers of ticks together in porous envelopes and placed them into a chamber with low humidity. The low humidity killed most of the ticks except those that were in the biggest clusters. Thus, our experimental evidence supports the theory based on observations in nature.

Technical Abstract: Low relative humidity (RH) levels (=63%) have been previously shown to be a determining factor in the survival of southern cattle fever tick, Rhipicephalus microplus, larvae, regardless of temperature. Supporting this observation, large larval clusters can retain more water than isolated larvae. Thus, the goal of this study was to identify if cluster size plays a role in the survivability of R. microplus larvae exposed to low RH. Initially, 14- day old larvae were placed into individual packets inside enclosed terrariums. A total of 48 packets were made and divided into 3 groups: one group of 16 packets contained low numbers of larvae (=10 larval ticks, LOW group), another group of 16 packets contained intermediate numbers (~100 larval ticks, INT group), and the other group of 16 packets had high numbers (=200; HIGH group). The packet groups were split and half placed in an enclosed terrarium with an internal RH of 55%. The other half of each packet group, served as controls, and were placed in an enclosed terrarium at a RH of >75%. After 5 days the numbers of live and dead larvae were counted to determine the percentage of larval survival in each group. All larvae survived in each of the 3 groups in the control terrarium. In the low RH terrarium, no larvae survived in the LOW groups (0%), the INT group showed a low rate of survivability (0-32%), and the HIGH group had the largest survival rate (28-74%). Overall, these results indicate that larger cluster sizes increase larval survival under low RH stress.