An update on scarab beetles and the damage they can do in the garden

After writing about the fig beetle – a shiny green scarab beetle that feeds on overripe fruit and decomposing organic matter – I received the following email from Elizabeth Russell, who gardens in Newport Beach.

She writes, “I am a past board member of the California Rare Fruit Growers (Orange County chapter), and have a degree in Agricultural Science. Despite the repetition of certain claims on the internet, fig beetles are NOT innocuous. The grubs are deadly. When fig beetle eggs hatch, the grubs/larvae feed on decomposing material. Unfortunately, they also feed voraciously on the finer plant feeder roots. Due to root decimation from larvae over the course of two seasons, I have lost a prize Washington navel orange tree that was 20 years old, a dwarf Meyer lemon tree and Big Jim loquat tree that were around five years old, and a Frederick passion vine that was one and a half years old but had grown up super fast.  

“After using fermented fruit unsuccessfully as a trap (I was attracting every beetle in town), I finally found it most successful to wage war with a parasitic drench: Thuricide BT. It is designed for caterpillars but works on beetle larvae and does not harm earthworms. I spoke directly with the manufacturer to confirm the latter. Please help educate the public and save our fruit trees.” 

Russell closed by offering this tip: “Should you remove your fig trees, the beetles will tend to leave your garden alone and the grub issue will be resolved. You can also plant trees with fruit they don’t like. They have weak mouthparts and prefer soft or soft-skinned fruit. The beetles don’t seem to be interested in my apples. They loved my grapes, but the roots were not affected by grubs, perhaps because grapevines go dormant.”

Thuricide, the product Russell recommends, is a biological control agent. This means that it is a living organism that preys on another. In this case, the control organism is a bacteria known as BT (Bacillus thuringiensis). According to the label, Thuricide BT “has no effect on birds, earthworms, or beneficial insects such as honeybees and ladybugs, when use as directed. Acceptable for use on edible plants up to the day of harvest.”  

As to soil-dwelling larvae such as those of fig beetles, Thuricide is applied as a drench, soaking it into the soil around the drip line or canopy perimeter line of the tree. It also comes in handy when controlling those white cabbage butterflies that lay their eggs on the foliage of cole crops, especially cabbage.

There is another insect that, contrary to popular belief, is not entirely benign. This would be the praying mantis. At the outset, however, it must be said that the sight of a praying mantis is just plain riveting. What a magnificent creature to behold! It is so much larger than any other garden insect and, with its well-defined triangular head, has this E.T. (extra-terrestrial) aspect, as though it descended from another galaxy. You cannot cease to wonder in amazement at this special visitor. And yet, not content to simply gaze at this unorthodox insect, you will probably begin taking meticulous mental notes of the circumstances that have brought this predatory arthropod – a relative of grasshoppers, katydids, and crickets – into your garden. 

First of all, there is the plant itself in which your praying mantis resides. More likely than not, this plant has lots of dense interior growth within which the insect finds shelter and where it can deposit its eggs, protected from the elements and hungry birds. There are probably plenty of other insects around as well.  Mantises require live insects for food but their diet is diverse, consisting of flies, crickets, moths, caterpillars, cockroaches, and any of the so-called true bugs — boxelder, milkweed, and shield bugs, to name a few. 

Numbered among praying mantis victims, you will find the “big five” of garden pests. The big five all do damage the same way, by sucking sap from leaves, stems, and fruit. These five pests are scale, whitefly, aphid, thrips, and mealybug, the first letter of each conveniently found in SWATM, a handy acronym by which to remember them. You can order praying mantis egg sacs from a wide selection of Internet vendors, including planetnatural.com. A single egg sac, known as an ootheca, may contain up to 400 eggs. After placing the egg sacs in your plants, refrain from chemical spraying which will invariably decimate your newly hatched mantids.

There are two broad categories of insects, based on whether their metamorphosis is complete or incomplete. Insects with complete metamorphosis undergo four life forms: egg, larva (caterpillar in the case of butterflies, grub in the case of beetles and bees, maggot in the case of flies), pupa (chrysalis or cocoon in the case of butterflies), and adult. Incomplete metamorphosis includes those insects that emerge from the egg in a form that will be maintained throughout their lives, except that they will grow in size, molting or sloughing off their exoskeleton from one instar or developmental stage to the next. As an example of an insect that undergoes incomplete metamorphosis, the praying mantis molts up to nine times over a period of five months. In the final stages of growth, the exoskeleton becomes so hard that the mantis may die extricating itself from it. 

 A praying mantis may be either green or brown and it is not conclusively understood why this is so. It is thought the environment contributes to its color since you may find a brown mantis among fallen leaves and dead grass and a green mantis among newly expanded green foliage. Humidity may also play a part, with brown mantises present when humidity is low and green ones when humidity is high. Mantises can also change color as they molt. Nymphs are always brown and females are more likely to turn green. When nymphs hatch from their egg sac, if they do not find other insects to eat within a week, they will consume one another. 

Praying mantis mating habits are sometimes unusual. In certain species, the female tries to eat the male’s head during mating and may consume the entire male after that. If the male does not manage to get away, it will continue to mate for several hours in a headless condition. Female mantises of some species can reproduce asexually –the process is known as parthenogenesis – and thus do not need to mate. In their case, eating a male provides the nutrients and energy required for them to lay eggs.

California native of the week: Chaparral sage (Salvia clevelandii) is perhaps the most aromatic and the most heavily flowering of all native sages. Its small grayish-green leaves and bluish-violet flowers are redolent of a musky perfume. Long floral spikes are stacked shish-kebob style with whorls of blooms. Although it blooms mostly in late spring, it may flower again for several weeks at this time of year. Chaparral sage is extremely drought tolerant and should never need more than one deep soaking per month. After two years in the garden, it will thrive on winter rain alone. It has a mounding growth habit, reaching five feet tall and eight feet wide with cold tolerance down to 15 degrees. Several varieties are available, with Allen Chickering notable among them. This species was utilized by Indigenous peoples for curing respiratory ills, dressing wounds, and treating poison oak infections as well as for smudge ceremonies. Chaparral sage is widely available in the nursery trade.

Do you have a garden insect experience you would like to share with readers of this column?  If so, please send it along to joshua@perfectplants.com.  Your questions and comments, as well as garden problems and successes, are always welcome.