Effects of cannibalism on life history decisions of larvae of beetles.

Amos Bouskila, Pablo Blinder and Ally Harari

Tenebrio molitor is a Tenebrionid beetle found in grain storage facilities in many countries throughout the world. Its life cycle takes about 3 1/2 to 5 months (at 29 degrees C) from egg to adult through several stages of larvae including a period of 10 days of pupation. During pupation, the pupae are totally helpless against cannibalistic individuals that may attack them. The larval stages are not fixed in number, and pupation can be delayed under certain conditions. The risk of cannibalism on pupae is higher from adult beetles then from larvae, and higher from dehydrated beetles compared to non-dehydrated individuals. Inaddition, there is a risk of cannibalism on eggs by larvae, that may consume almost 50% of the eggs mixed in the substrate during one week. I hypothesize that T. molitor may be able to reduce the risk ofcannibalism by choosing the time and the location of pupation. There are tradeoffs involved in the pupation timing: for example, individualspupating early may reduce the chances that their pupae will be attacked by adults, but at the same time they may emerge as smaller adults (i.e., will have fewer eggs during their life time) and their eggs may be exposed to cannibalism by other larvae that delayed their pupation. The decision of the larvae when to pupate may be affected by the external conditions (availability of food and water sources) but there may be several strategies for selecting pupation time that are equally successful.

There is a possibility that individuals take into consideration what other individuals are likely to do, and this may indicate that a game situation may have evolved among these beetles. In this study I collect data on the life history of the larvae, and perform experiments in several directions in order to understand what determines the decisions of the larvae. The ultimate goal of the study is to construct a mathematical model for the life history stages of T.molitor , and to use the model to understand the main factors operating on the determination of pupation time.