Manduca, along with the beetles, ants, bees, wasps, flies, and mosquitos, display the form of development seen in many insect species, a complete metamorphic change. The adult looks much different than the larva and pupa. Holometabolous insect like Manduca start life as an egg, then emerge from the egg to feed and grow as a larva. The insect then metamorphoses into a pupa and undergoes extensive reorganization of the body plan to emerge as an adult.
- The egg of Manduca is round and smooth.
- Eggs are about 1.5 mm in diameter and weigh approximately 1.4 mg.
- Females usually lay one egg per tobacco leaf primarily during the evening hours.
- The females curl their abdomen under the leaf and attach the egg with a glue-like substance.
- A female can lay upwards of 700 eggs during her life time.
- The fertilized egg undergoes rapid development, and emerges in about 120 hours.
- The new larva is pale yellow-green and displays a very long horn.
- The horn is often longer than the body.
- The larva uses its large mandibles to chew a hole in the chorion (egg shell) and climb out to eat the remaining chorion.
- Manduca display five instars during the larval stage.
- Under ideal conditions (78 degrees) larvae will hatch in about 120 hours.
- The cooler the surrounding temperature, the slower the insects will grow.
- First-instar (1:19 minutes; 4.4 MB)
- Second-instar (0:41 minutes; 2.3 MB)
- Third-instar (0:17 minutes; 949 KB)
- Fourth-instar (4:46 minutes – hosted at YouTube)
- Fifth-instar (0:52 minutes; 2.5 MB)
- Manduca goes into a wandering stage once it has stopped feeding.
- In nature the insect burrows into the soil.
- In our project the wandering Manduca is removed from the food, washed and dried and placed in a toilet paper roll. This is done so we can see the pupation process.
- Just before pupation, the larva develops a set of brown bars on the thorax.
- These metathoracic bars are visible about 12 hours before pupation. You can see the split in the bars at the center line of the insect. Along this line, the insect will break the old cuticle or skin and wriggle out over a period of several hours.
- While molting, the cuticle or exoskeleton of the pupa is transparent, and it is possible to see through to the hemolymph (blood).
- This transparency gradually decreases as the insect’s cuticle begins to harden.
- Over the next 24 hours the cuticle turns brown. The cuticle color is formed by a chemical hardening process (sclerotization).
- The length of time spent in the pupal stage depends upon the hours of light received by the larva.
- If a larva is exposed to 12 or less hours of light, (late summer conditions), the insect will go into the diapause phase and remain underground for 8 to 9 months.
- If the insect is exposed to 13 or more hours of light (early summer conditions), it will not go into diapause and will begin development immediately. This process takes about one month to complete.
Adult moth stage
- The insect emerges from the brown pupal case with it’s wings deflated and soft.
- The wings must be stretched out before they are ready for flying.
- The moth climbs a stick and lets the small uninflated wings hang behind it. Gravity and pumping of fluid into the wing veins inflates the wings; sclerotization (hardening) then occurs to make the wings rigid.
- This takes about 6 to 8 hours and usually happens during the evening or night.
- When the insect is ready to fly, (usually at dusk or night) it shivers to increase its body temperature to about 98 degrees F and then it is able to fly.
- The adults typically live about a week, feeding entirely on nectar from flowers.
Are all insect life cycles the same as Manduca?
No. Not all insects follow this pattern of development. Insect development can be describe as ametabolous, hemimetabolous, and holometabolous.
Holometabolous insects, like Manduca, undergo a complete metamorphic change during their lifetime.
The ametabolous insects emerge from the egg looking like the adult, only smaller. Insects in this group don’t have wings. These are some of the most ancient of the insect Orders having evolved better than 400 million years ago. Although they evolved along with the trilobites, they are still with us, indicating that they have been successful in adapting to an ever changing planet.
The hemimetabolus insects are insects that emerge from the egg looking similar to the adult but they don’t have wings and genitalia. The wings develop in small clumps of tissue outside the body wall. At the final molt to the adult stage, the wings become fully developed. Good examples of the hemimetabolous insects are the roaches, grasshoppers, stink bugs, and dragonflies.