Effects Of Cantharidin-Related Compounds On Plutella Xylostalla

Cantharidin is a kind of sesquiterpenoid mostly found in Meloidae,acting as a natural defensive toxin.It attracts attention of researchers recently in the field of plant protection because of its excellent activity against pests,harmful fungi and weeds.Due to restriction of natural cantharidin resources it will be a most important way to develop cantharidin-related compounds with high activity and easier synthesis process.Apoptosis-like symptoms of tissues was observed in cantharidin-poisoning larvae of Plutella xylostella and Mythimna seprata.Cantharidin can also regulate specific activity of AchE,CarE in larvae of Plutella xylostella and CarE,ACP,ALP,GST,cytochrome P450,PPO in larvae of Mythimna seprata.And ALP was thought as a prospective target of cantharidin according to previous study.Stomach activity of 82 cantharidin-related compounds were primarily tested against 3rd-instar larvae of Plutella xylostella with leaf dipping method,and the LC50 of 27 of these compounds were obtained and relation of structure to insecticidal activity clarified after further examinations.Additionally,effects of cantharidin on ALP of 4th-instar larvae of Plutella xylostella were examined either in vitro or in vivo to further reveal mechanism of cantharidin induced toxicity in insects.The main results are as follows:1.Two methyl play important roles in the activity of cantharidin and its acid form,and their activity are significantly different from other cantharidin-related compounds provided in this study.2.Cantharidin-related compounds in ring-opened form or easily coming up with hydrolysis at the cyclic anhydride are more active.3.Cantharidin(Ⅰ)(LC50=12.74mg/L)and its acid form(Ⅱ)(LC50=13.77mg/L)have no significant differences on activity,norcantharidin(Ⅲ)(LC50=140.47mg/L)and its acid form(Ⅳ)(LC50=129.35mg/L)have no significant differences on activity.4.Variation of electron density distribution of electron cloud and stereohindrance effect caused by substituent have important impact on the activity of cantharidin-related compounds,especially for which located near the ketonic oxygen,and the activity of Ⅶ-28(LC50=134.43mg/L)is not significantly different from norcantharidin.5.Larvae poisoned by cantharidin-related compounds showed same symptoms.6.Cantharidin caused significant decline of the specific activity of ALP in 4th-instar larvae of Plutella xylostella in vivo,and declining ratio rose during continuously poisoning,however,cantharidin cannot cause variation of the specific activity of ALP in crude extracts in vitro.