Hi,

There are some answers (in French) in:

Poitout, S., & Cayrol, R. (1969). Action de differents facteurs sur le nombre de stades larvaires chez la noctuelle de la tomate Hilicoverpa armigera Hbn. Soc Entomol France Ann, 1969.

Best regards

Thanks Samuel.

I am trying to access the full paper of the same. In the mean time i also accessed some interesting papers on influence of diets on instar numbers of Helicoverpa armigera https://www.jstage.jst.go.jp/article/aez/35/1/35_1_69/_pdf

and

General review on factors that can induce intraspecific variations in instar numbers in insects.

http://www.zoologi.su.se/research/nylin/Esperk2.pdf

with regards,

Dr. Bob Fye, who was a scientists with the USDA, conducted a series of rearing experiments for a number of lepidopteran species that are herbivores of cotton, including H. zea and H. virescens, If I remember correctly, he reported the effects of several environmental variables on developmental duration, number of instars, and other biological variables.

I've observed variable instal numbers from field collected larvae in California, Texas, northwest Mexico, and eastern Australia. The number of instars is affected by food quality, temperature, and presence of pathogens, at least for H. sea, H. virescens, H. armigers, and H. punctigera. Increased stress appears to increase the probability of one or more additional instals being produced, at least for these species.

Thanks Prof. Wilson for sharing your experiences and citing the work of Dr. Bob Fye which are very useful in this discussion.

The work of Dr. Bob Fye is available as a book in http://books.google.co.ke/books?hl=en&lr=&id=QH-yGAoVbCMC&oi=fnd&pg=PA1&dq=Robert+Fye&ots=V1dYzjeW35&sig=mDmnW72j5ltRq3LxCwBDcMeEbk4&redir_esc=y#v=onepage&q=Robert%20Fye&f=false

Dear Sevgan, I tried to get the first link regarding papers on influence of diets on instar numbers of Helicoverpa armigera, but failed. Could you please send the paper to [email protected] ? I would realy appreciate it. Thanks!

Dear Sevgan,

Can you send me the PDF of the book chapter where The work of Dr. Bob Fye was described...my [email protected]

it will be a great help....Thanks in advance.....

Amit

http://books.google.co.ke/books?hl=en&lr=&id=QH-yGAoVbCMC&oi=fnd&pg=PA1&dq=Robert+Fye&ots=V1dYzjeW35&sig=mDmnW72j5ltRq3LxCwBDcMeEbk4&redir_esc=y#v=onepage&q=Robert%20Fye&f=false

As I know, here in China, H. armigera usually has 5-6 instars. The most larvae on pea and sunflower have 5 instars, many on corn, cotton, wheat and tomato usually have 6 instars. The larvae on the artificial diet in my lab have 5 instars.