Pictured above: Coleoptera Nitidulidae

Some macadamia processors are counting the cost of increasing incidences of sap beetle or dried fruit beetle Carpophilus spp. (Coleoptera: Nitidulidae) on nuts coming into their plants.

While little research exists on the unassuming sap beetle (Carpophilus), industry scientists suggest in the SAMAC (South African Macadamia Association) article that unexpectedly high rainfall and wet conditions during the past season could have played a significant role in rising numbers of the insects reported by some processors.

“The beetles have been observed on macadamia nuts for some time, but numbers and concomitant damage levels had been low. Things changed this season when several processors reported problems simultaneously,” the article says.

The insects are associated with varied cropping systems in wet environmental conditions, said the scientists, who theorised that the current high numbers were linked with the abnormally high rainfall this past season. “Prolonged wet conditions may have led to the nuts remaining on the ground for longer, resulting in decaying husk tissue that created perfect conditions for the beetle to thrive,” they said.

Walnut and almond impact

A 2019 research report in Campania, Italy, after an outbreak of the sap beetle C.truncatus on stored walnuts, delivered concerning findings.

Inspections in walnut warehousing uncovered numerous beetles (larvae and adults) on the stored nuts. They were identified as belonging to the genus Carpophilus Stephens (Coleoptera:Nitidulidae). Reports have also emerged of “unprecedented damage by Carpophilus on stored walnuts in Argentina and almonds in Australia.

“A Geographic Profiling approach has determined that the more virulent population was first introduced in Italy… climate conditions where C. truncatus is currently widespread and harmful indicate that the world’s entire walnut production is in jeopardy, as this species could adapt to any of the main walnut and almond production areas,” warned the scientists.
While online literature describes the beetles as a worldwide pest on fruits and grains, Wikipedia declares they are native to North America, Oceania and Europe.

Carpophilus hemipteris was first recorded in South Africa in 1979. It is presumed that due to an absence of natural predators, populations increased rapidly, with records of significant infestations in different seasons.

Further online research by The Macadamia revealed little in the way of information on natural predators.

Cactus pear damage

In a 2009 research paper titled “Bio-Ecology of Sap Beetles (Nitidulidae), a new double impact pest on Cactus Pear in South Africa”, authors S. Louw, J.V. Parau and J.C. Olevano describe the insect as a “known agricultural pest of numerous field and stored products”.

They say in the cactus pear, Carpophilus spp. (Coleoptera: Nitidulidae) is responsible for “wide-ranging direct (feeding) and indirect (disease transmission) health pressures on the crop”.

Further research by agronomists INCroP recorded three species (Carpophilus hemipterus, C. ligneus and Urophorus humeralis) on plants in the central Free State.

“The cosmopolitan C. hemipterus was quantitatively dominant throughout all the surveys. In this study, C. hemipterus bred prolifically in fermenting fruit, with the adults sheltering under the decaying, moist cladodes (fleshy stems or leaves) that had dropped from the plant. This species also transmits a wide range of diseases to the cactus pear plant,” the researchers said.

In the SAMAC article the beetles are described as small – about 3mm long – broad and flattened, with shortened wings that leave between one and three segments of the abdomen exposed.

Macadamia impact

“Although little is known about these beetles in South Africa, infestations are believed to originate in the field before they are transported to the (macadamia) processing facility, where damage becomes significant,” the articles states.

While there is no dedicated research in this field, Nelmak varieties were found to harbour large numbers of the beetles.

This is presumable because nuts of this cultivar tend to split open along the suture line when approaching maturity, SAMAC said.

The Sap beetle larvae are about 6mm long and cream-coloured. The head capsule and end of the abdomen are dark brown. The larvae have three pairs of true legs as well as horn-like structures on the anal end. Larvae can be found feeding inside the husk on decaying tissue: they enter the nut either through the hilum, sometimes even through the shell.

Damage to the macadamia shells includes partially constructed holes – in severe cases a shell may have several holes. “Once inside, the larvae consume the entire nut, turning it into a meal-like consistency,” the article reported.

Prevention better than cure

Prevention methodologies include early harvesting, meticulous sanitation and short nut pick-up cycles, which are believed to reduce the food source for the beetles. “These insects have a very wide host range and the presence of any over-ripe or fermenting fruit in or near a macadamia orchard may lead to higher numbers of the beetles.”

Because they are attracted to mouldy or fermenting fruit, bucket traps can easily be made on-farm that will lure large numbers of the insects. Buckets filled with rotten fruit, some water and yeast are ideal if the buckets are deeper than they are wide, to make sure the beetles are unable to escape.