Stephen Gourley visited the Department of Applied Mathematics at Hong Kong Polytechnic University from 5 April to 14 April for research interaction with Prof Yijun Lou.  Stephen and Yijun are developing new approaches to modelling competition among the larvae of disease-carrying insects such as mosquitoes. If larvae grow at a rate that depends on how many other larvae are present at each stage of development, and mature only on reaching a certain size or weight, then the developmental time for larvae is determined by an integral constraint known as a threshold condition. This approach to modelling larval development is more realistic than classic approaches which assume they mature after a fixed period of time.