I would like to share some of my observation during the collecting activity. Right now, it's about Mr. Prepupa. Ladybirds are holometabolous insects which means, before they become adults, they must undergo larval stage. This is a challenging phase for it as it must thrive the surrounding for at least the next four larval stages (instars). Last time during the collecting, I found that there were so many larvae of zig-zag ladybirds on corn in response of the aphid, Rophalosiphum maidis. I also found there were many larvae that were turning into pupae but just died. They are known as prepupa. I knew they were dead because when I touched them, they did not move at all like the normal one. And when I squeezed them with a gentle crush, they shattered as if they were hollow. The same thing also happened yesterday when I went to look for C.transversalis. I found the prepupae also exhibited the same problem. They were attached to the leaves, stood still but when were touched, they did not give any response. And when I crushed them, they shattered. I am not sure what cause this mortality. I did not find any parasitoids around nor the larvae of them. Is it because of the weather (temperature, humidity)? Perhaps, it is...Probably the dehydration problem? However, there might an explanation to this phenomenan, that is cannabalism. Cannabalism is typical in ladybird life cycle especially when the food is scarce. According to the book (Insect-predator prey dynamics: Ladybird beetles & biological control), prepupal and pupal stages are the vulnerable period for them as they are succumb to cannabalism. Osawa (1992b) reported that pupae of ladybird, Adalia bipunctata, pupates on the trunks at some considerable distance from the leaves that have aphids resulted in lower pupal mortality. In other words, the more the larva pupates near or at the patch of food prey, the higher the possibility to get cannabilized by other larvae or adults, and the higher the mortalilty is. It is also said that, those prepupae that move off the host plants and pupate on the adjacent plants undergo lower parasitism. This would be a good explanation to my obrsevation above. I realized now that it is a dangerous buggy world out there for a ladybird to survive naturally. What if you put yourself in their situation, do you think you can survive successfully? Think about it.......
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