Vietnam hibiscus flower eating beetle

[roadrunner]

David,

Haven't been able to identify your beetle even at a good website devoted to beetles of Vietnam.  It isn't the dreaded Australian hibiscus beetle. It is similar in appearance to some nasty scarabs that made mincemeat of several of my rose blooms for a few weeks this summer. They came and feasted then disappeared. I hand picked and killed as many as I could. It was the first time I'd ever seen them. You may also have this problem for a short length of time.  It is important to kill as many as possible obviously to stop the monsters from destroying those beautiful flowers, but also to hopefully prevent additional infestations. Scarabs spend more of their life cycle in the larva (grub) stage so the adults are fairly short lived. The adults eat, lay eggs in soil, and die. The grubs feed on roots, pupate, then emerge the following year. That's typical for temperate areas. In more tropical climates like yours they could have more than one generation per year. Just a guess.

Are there any entomologists on this forum?

I just found my Spinosad. The label says it's supposed to be effective against beetles so I'd use it, but since the beetles are getting inside the buds and blooms I'd also hand pick and kill as many as possible. Find out if any other hibiscus in your area are infested to hopefully determine if the beetles are native to your area or are only your collection's infestation. If your plants are the only ones being infested then it could be an import which arrived in some other plant that you've purchased. I would doubt your plumeria has anythng to do with this.

Hope this helps a little.

dave

[davidwood]

Dave I have been answering in the wrong place, no doubt you have read it so I wont repeat it.
I was wondering, especially after you say it may lay its eggs in the soil if it would be a good idea to clean the soil, did you do anything for your Rose's.
I was thinking a good drench with bleach [hydrogen peroxide], maybe I will ask Charlie if this is a good idea and if it is whats the max I can get away with, I know its been discussed before about cleaning fungus in the roots but I have forgot.
So Charlie if you read this how much bleach can you add safely to a gallon of water? and do you think it would kill beetle eggs in the soil.

Below is another picture of it, and its about the size of my fingernail.

[roadrunner]

Treating your soil would be a question best left for Charlie.  That is definitely an area that is out of my field of expertice.  I don't think I'd consider that unless you have a large number of beetles and if it is a local species that might not help much.   Since they are attracted to your plumeria I wonder if they feed on pollen also? Spraying with Spinosad and hand picking may be enough.  It's best to use the least toxic methods when possible.  Also, many scarab beetles are nocturnal and are drawn to lights.  Check for them around lights at night and if they're there, put those size 9s to work. Too bad we don't know which species it is and what it's host plants are, etc.

As for my roses I basically tried to kill as many of the beetles as I could find in the blooms and under my porch lights at night. After about 3 weeks they disappeared.  I have about 130 rose bushes in containers and planted in the ground so any kind of soil treatment for them would have been a major task.  I also have 3 dogs so I use pesticides sparingly. If I have a larger invasion by them next year then I'll need to try something more aggressive I suppose.

dave

[Charlie]

David, I am always hesitant to use bleach in the soil. The hibiscus can take it (surprisingly) but you kill off a lot of the beneficial microbes that are in the soil. If you decide to try it mix 1 part of regular household bleach with 8 parts of water or in US measurement 1 pint of bleach to 1 gallon of water. US household bleach may not be the same strength as what is available to you - not sure about that so you better check it out. You might be able to find acephate in Vietnam. That is a pesticide that can be drenched into the soil and was common around the world for decades. Not sure if it would kill beetles but it is a wide spectrum pesticide (stinks though so only use it outside).

Charlie

[roadrunner]

David, just curious. Are you having any success getting rid of those nasty beetles?


dave

[davidwood]

David, just curious. Are you having any success getting rid of those nasty beetles?
dave

Dave they have gone which is good, problem is I am not sure weather its my spraying with Spinosad thats stopped them, or that the Plumeria which I think first attracted them has stopped blooming. I supose I will find out if its the Plumeria if the Beetles  come back when it blooms.
I am quite lucky that my garden is on the roof of a house, I get a little less bothered with things than I would if it was on the ground.

[roadrunner]

Very glad to hear that.  It could be the spinosad or maybe their few weeks of being a nuisance has past. There are several species of scarab beetles around here the show up for a few weeks then disappear.  The adults are short lived so those that do any damage don't persist for very long. The spotted cucumber beetle on the other hand starts nibbling on just about anything that blooms as soon as it warms up in the spring and I'm still finding them in the rose blooms this week.

dave