If your mummies are on the underside, there are several possible reasons for that. The reasons that I can think of (precoffee/breakfast) in order of probability: (1) The weather was inconducive for proper husk formation. (2) Adaptation to the ants. (3) The parasite did not move the host fast enough before the host brain stopped functioning. (4) A hyperparasite with different plans.
(1)Here on the East coast we get days on end of glorious sunshine. The top side of the leaf is the optimal place to be in order for the exoskeleton of the aphid to dry. Dry is what is needed for the parasite to complete its metamorphosis.
I have always lived on the East coast; my understanding of the Maritime North West (along with the British Isles and Tasmania) is that it is very rainy/foggy. Wet gray days...kind of like a perpetual spring over here. Thus, the underside of the leaf would be a better place to finish metamorphosis.
(2)The ants. If an aphid cow acts odd and separates from the rest of the herd it will attract the ant overlords attention. So for self-preservation reasons, the parasitoid has learned to pupate amongst the rest of the herd on the underside of the leaf.
(3)The host's nervous system gave out. Pretty self explanatory...no need to delve there. Although, this book I am writing seems a bit dry...and this is a forum and forums are part information, part entertainment...
So! For your gory entertainment imagine if you will that you yourself are the aphid and there is something in your abdomen that wiggles around every so often. You think its just gas and continue on your aphid ways inserting your stylets into a plant leaf and sucking out sugary water from the plant you are attached.
Nothing seems amiss as you sway in the breeze surrounded by your sisters as your mother gives birth to yet another sibling. Then that wiggly feeling in your abdomen wiggles more. Perhaps your wing bugs are starting to grow! The thrill at the prospect of finally becoming an adult is shattered with a sharp pinch in your stomach. That is the wrong place for wing buds. More wiggling. Something is wrong, very wrong. Another pinch, this time closer to your head. Your central nervous system is being hijacked. Like a zombie you are no longer in control. Your limbs are flaying, your stylets have snapped.
The thing inside you with its hooks sunk into your brain is moving you. Away from your mother and sisters. Its moving you to the top side of the leaf. Into the sun. In an odd way, you are thankful. Your misery will be over soon as the sun's rays dessicate your soft body.
(4) Hyperparistoid. Which is another book.
and I need breakfast lol
Disclaimer: The word *you* is used in a collective manner, not *you* in a personal/directive manner. No Aphids were harmed in the creation of this story. Any similarities to actual persons/aphids was coincidental. All rights reserved. Ha!