Green Beetles under the Microscope

If you ask most people, they would say that almost all species of animals are already known -except for a handful at the bottom of the ocean or deep in the jungles. A group of students at South Texas College knows that isn’t true. They are working on a project with Dr. David Robacker at the Weslaco campus to identify new species of beetles from Mexico. Every week on Friday afternoon students from the Dual Enrollment Medical Science Academy (DEMSA) gather in a laboratory with their microscopes to dissect and examine green-, white- and red-striped jewel scarabs that live in montane pine forests all over Mexico. Right now, and since the species was first described scientifically more than 150 years ago, these beetles have borne the name Chrysina adelaida. Members of this genus Chrysina comprise a group that includes species from Texas and Arizona all the way through Central America to Ecuador. Many of the species are metallic gold or silver, but the species in Mexico are mainly green. Right now there are about 120 known species according to experts Dave Hawks (Riverside, CA) and Jose Monzon Sierra (Guatemala City, Guatemala), but everyone who loves these magnificent insects believes there are many more waiting to be recognized. Most of these probably live in remote mountains where roads don’t exist and scientists rarely go. But our students know that some new species may be right under our noses.

Last year, students Norma Barrientos, Brianna Miranda, Naidely Castillo, and Esmer Aguilar began the work and took it to a point where emerging evidence implicated one particular population (sorry, can’t say where due to proprietary considerations) as different from nominate C. adelaida in central Mexico. Most of those students have since moved on to new adventures. Enter current team leader Naidely Castillo and fellow students Alejandra Escobedo, Nathan Martinez, Galilea Casas, and Guadelupe Martinez who plow through genitalic microdissections with ease to look for morphological differences that distinguish populations from different places as probable different species. The premise of the work is that if male genitalic capsules and female genicalic plates differ between beetles from different places, they must be different species. This idea is based on a long-held tenet called mechanical isolation that means different species may have different genitalic structures that prevent them from mating with each other because they simply don’t fit together during copulation.

So, are there any morphological differences? The students can tell you that it is hard to discern by looking so we turn to careful quantitative methods. Math always seems to be the answer. Using a powerful dissecting microscope equipped with a built-in camera system (courtesy of the STC Biology Department), the students obtain images precise to tenths of a millimeter and determine the sizes and angles of the genitalic structures that simply could not be measured another way. Naidely has witnessed the results for 6 males from the nominate population compared with 7 from the study population and she can attest. “Yes, we can see that they are different” referring to males from the two groups. Statistical analysis of the data confirms what she observed. “It is exciting to realize we are discovering new species that no one else even knows about”.

There is still a lot of work to do but the research is progressing quickly to a conclusion – maybe by the end of spring semester 2020. “The reward is knowing we are doing science and seeing that these beetles are different, and then that the species we are discovering will get a name that will last forever”, says Naidely. Indeed, the students themselves will get to suggest a name that will become part of the legacy of Chrysina taxonomy.