This paper aims to model the biodiversity trends of three species of insects found in Mt. Arayat National Park. The biodiversity trends of Coleoptera, Odonata and Arachnida follow the law of natural growth and natural decay which were used to model the biodiversity trends and governed by the Differential Equation = = kP with a general solution of P(t) = Pye*-*). The traditional way of solving was used to manually solve the particular solution, and the growth decay rate of the three species. Also, the researcher developed a program of the model using SCILAB program. The data revealed that 15 species of Coleoptera will be facing population growth while the other 11 will experience population decay. Meanwhile, the population of eight Arachnida species will grow and the other five will decreased in number. Also, eight of the species under Odonata will multiply in number as projected on the model while the other three will be at risked. The projections are solely determined by mathematical models using population as main variable. Existing environmental factors of the study site are strongly recommended to be considered in conducting further analysis. Keywords: Coleoptera, Odonata, Arachnida, trends, differential equation.