Changes in the Mechanical Properties of the Cuticle of Triatoma Infestans associated with the ingestion of food 

Introduction

          The mechanical properties of the cuticle of some insects could vary in a quick manner.  The larvae of many assassin bugs are capable of taking in a single ingestion a quantity of blood so great, that it represents many times its own weight.  During ingestion, the abdomen expands considerably, allowing it to enlarge its surface more than 4 times its size and making its cuticle very thin.  Not only are the elastic segmented membranes expanded, but the abdominal inner cuticle is made "extensible."  This phenomena is known as the "plasticization" and is associated with a decrease of the cuticle pH which from a normal state of above 6, is made smaller than this value.  This decrease of the pH is sufficient to break weak junctions between microtubules of protein and chitin, which could then be slid over one another.  This change is temporary and after some time, the pH, the molecular junctions, and the mechanical properties of the central nervous system and endocrine factors that respond to the signals associated with the detection, approximation, and contact with the host.

          In this practical work, there will be practices performed that will allow to show evidence and to quantify the modifications in the mechanical properties of the cuticle of the assassin bugs Triatoma infestans associated with ingestion.  There will be attempts to correlate the physiological changes with the morphological changes encountered by the plasticized cuticle.

Objectives

          To analyze the mechanical properties of the cuticle of the assassin bug Triatoma infestans and its modification by the ingestion of food.  To observe the morphological changes produced in the cuticle structure related with the plasticization process.

Materials and Methods

- The figure represents the device that will be used in these practices and it consists of: mercury manometer, graduated pipette of 1 ml, metal cannula of 0.3 mm in diameter, 3 ml syringe to apply pressure to the manometer, T connections, rubber hoses, Mohr forceps.

- Triatoma infestans, larvae of the 5th state, not fed.

-Ringer solution for insects (case modified, 1957):    Base solution: 1000ml of distilled water, 7.5 g NaCl, 0.14 g NaHCO3, 0.35 g KCL, 0.21 g CaC2, 2.5 g glucose.  Take to PH 7.0  buffer: 0.15 molar solution of KH2PO4, 0.15 molar solution of Na2HPO4.  Ringer: 10 volumes of base solution + 1 volume of buffer.

-Dissecting forceps

-Artificial feeder

-Cow's blood

-Bough of magnets

-Micro cauterizer

-Paraffin

-Absorbing paper

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