Insect Pupae and Larvae Size Separator

• Causes: The causes of size dimorphism in insect larvae and pupae are not allways fully understood, but are likely to be related to differences in mating behaviour, reproductive strategy and ecological factors. For example, larger females may have a competitive advantage in mating or may be better equipped to produce larger eggs.
• Developmental differences: Size dimorphism in insect larvae and pupae may be the result of developmental differences between males and females. For example, females may have a longer larval or pupal stage than males, allowing them to grow larger.
• Morphological differences: In some insect species, females have different morphological characteristics than males, which can lead to size dimorphism.

It is important to note that rearing conditions can influence the extent of size dimorphism in insect pupae. Nutrition is one key factor that can influence size dimorphism in insects - rendering a standardized feeding process imperative. Inadequate nutrition can lead to smaller body size, different feed application per tray will likely lead increased size heterogeneity and thus complicate sorting. Other environmental factors that can influence size dimorphism in insect pupae include temperature, humidity, and/or photoperiod. For example, low temperatures can slow insect development, while high temperatures can accelerate development. In addition, social factors such as crowding can also influence pupal size dimorphism. Crowding can lead to increased competition for resources, resulting in smaller or more heterogeneous body sizes. 

In summary, rearing conditions, including diet, temperature, humidity, photoperiod, and social factors, can all influence the extent of size dimorphism in insect pupae. In order to exploit size dimorphism to separate insect larvae or pupae using a size separator such as the IR-604 (or other methods, as illustrated below), it is therefore essential to maintain constant and optimized (diet, temperature, etc.) rearing conditions, e.g. in standardized rearing tray and rack systems, leading to most homogeniously sized larvae and pupae (per sex). 

• Sieving: Sieving is a simple and effective method of separating pupae by size. Pupae are poured into a sieve with a mesh size appropriate to the size range desired and the sieve is shaken or agitated to separate the larger pupae from the smaller ones. The separated pupae can then be collected and sorted as required. However, the mechanical stress on the pupae by sieving is high, resulting in frequent damage.
• Narrow plates: The narrow plate method, also known as Fay–Morlan glass plate separator, as used in the VSI IR-604 sex separator (see above), is another technique that can be used to separate insect pupae by size. Here a narrow plate of plastic, glass or metal forms a (an increasingly narrow) slit or slits of a specified width against another part. The width of the slit/slits can be chosen according to the desired size range of the pupae to be sorted. The mechanical stress on the pupae by narrow plate techniques is generally low, resulting in few damaged pupae.
• Density separation: This method separates pupae according to their density. Pupae are placed in a solution of a given density and the solution is then centrifuged or allowed to settle; partially iced water has been used to create density differences in a container. The larger and heavier pupae settle to the bottom, while the smaller and lighter pupae remain suspended in the solution. The separated pupae can then be collected and sorted. There is generally no mechanical stress to the pupae (unless centrifuged).
• Hand sorting: Hand sorting is a labor intensive but most effective method of separating pupae by size. Pupae are visually inspected and manually sorted into different size categories. This method is often used for small-scale rearing or research projects. Hand sorting is also necessary to select screen sizes and slit widths prior to, and to verify sorting accuracies after, using any of the above methods.

Overall, the choice of method for sizing insect pupae depends on the insect species, particularly the size range between large and small fractions, the resources and equipment available, and the volume of pupae to be sorted. The effectiveness and efficiency of each method should be evaluated and compared to determine the optimal approach for the specific application. Vienna Scientific is ready to assist in the design of automated, effective sorting systems, please get in contact.