Insect Diet & Rearing Information & Opinions: Food for Thought-Issue 1

Introduction

This column is offered by Dr. Allen Carson Cohen to call your attention to information and thinking relating insect rearing systems. Hopefully, it offers information useful to rearing professionals and is intended to evoke (and provoke) thinking about the complexities of diets and rearing systems. I hope that this thinking will improve your rearing efforts. I emphasize that these columns represent opinions and current thinking of Dr. Cohen and as such are not offered as or intended to be taken as reviewed research products. Although I am a strong advocate of publishing in refereed journals, I have that many useful aspects of rearing are difficult to publish as peer-reviewed papers. I also hope that it will stimulate thinking about how our company can be useful in consulting about these and related issues.

Allen Carson Cohen, Ph.D. and Director of IDRR, LLC

Diet “Ripening”

In a number of rearing facilities, one of the standard operating procedures (SOPs) is the “ripening” of freshly made diets. As is common for SOPs in diet domains, the reason behind the recommended procedure is obscure, usually derived from empirical means-somehow found to work with no explanation for why. Where ripening is an SOP, the diet is held for a period ranging from several hours to a couple of days, sometimes refrigerated, sometimes at room or rearing room temperatures prior to inoculation of the target insects.

The term, ripening does not imply merely cooling a diet that had been heat processed so that the target insects will not be heat-killed. Ripening refers to other kinds of changes that render the diet to be physically or chemically suitable where pre-ripened diets would inflict high mortality to the insects in question. The quest for understanding diet mechanisms leads to the question of what kinds of changes are involved in ripening?

One hypothesis is that a toxic substance evaporates or is otherwise disabled through the time-course of ripening. For example, if formaldehyde (37-40% formaldehyde solution = Formalin) is added to diets as an antimicrobial substance, which may also be toxic to insects (See Alverson & Cohen 2001). As the diet ages, some of the formaldehyde, which is moderately volatile, my evaporate or become degraded. The loss of formaldehyde may render the diet palatable.

A second hypothesis is that after diets are poured and allowed to cool, there is an expression of water from the diet gel. This process is known as syneresis (like what happens to yogurt after a few days in the refrigerator and watery material seeps out of the firmer gel). Syneretic water can trap and drown neonate (newly hatched) larvae. So allowing the water to evaporate prevents the losses that would stem from drowning.

A third hypothesis is that the texture of the diet is improved with a few hours of aging (texture includes the rheological properties such as hardness, gumminess, viscosity, elasticity, stickiness, cohesiveness, and many other facets of “mouthfeel”). We have found that the gel strength (as measured with a penetrometer) increases as diets ripen. Certainly, it is possible that all three hypotheses are valid, as well as several other reasons why diet ripening works to improve rearing success.

*This page was revised on January 5, 2009.