Developmental dynamics and survival characteristics of the common horse bot flies (Diptera, Gasterophilidae, Gasterophilus) in desert steppe

The genus Gasterophilus (Diptera, Gastrophilidae) is an obligate parasite of the equine family that causes widespread myiasis in desert steppe. Based on four common naturally excreted Gasterophilus larvae collected systematically in the Karamaili Ungulate Nature Reserve from March to September 2021, this paper studies the population dynamics and ontogenetic laws of horse flies, and discuss the coexistence pattern and population dynamics prediction of horse flies. The results showed that the Gasterophilus larvae had obvious concentrated development period, and the time of population peaks was different, the earliest was G. nigricornis (late March), followed by G. pecorum-I (mid-April), G. nasalis (late April), G. intestinalis (early May), G. pecorum-II (mid -August). The order of development threshold temperature "C-nigricornis < Cpecorum-I <= Cpecorum-II < C-nasalis < C-intestinalis" is consistent with the peak order of different larval populations. The life history survival rate (L) was as follows: L-nigricornis (83.97%) >= L-intestinalis (81.25%) > L-nasalis (72.42%) >= Lpecorum-II (71.65%) > Lpecorum-I (39.23%). This study combined indoor experiments and field surveys revealed the development of horse fly populations with different life strategies in desert grasslands. Based on the different development threshold temperatures of several horse flies, the staggered population dynamics of Gasterophilus form continuous infection stress on the host. In addition, G. pecorum exhibited a univoltine bimodal population distribution in this area and led to two high-intensity host infections, which is one of the important reasons why it has become the dominant species of myiasis in desert steppe.