Monkey beetles attack citrus fruit

SEAN MOORE1,2, MELLISSA PEYPER1, RIAAN STALS3 AND RIKUS DU PREEZ4 1

Citrus Research International, Port Elizabeth; 2Centre for Biological Control, Rhodes University, Makhanda;  3SA National Collection of Insects, Agricultural Research Council, Pretoria; 4Rikus Landbou, Patensie.

In October 2019, in the Gamtoos River Valley, Eastern Cape, numerous small beetles were recorded feeding on and damaging citrus fruitlets around the calyx end. The beetles appeared to be indiscriminate in their choice of cultivar, being recorded on lemons, Nova mandarins, Cambria Navels and Midknight Valencias. At this early stage of the season, the calyx had not yet closed on the fruit. As many as six beetles were recorded to feed simultaneously on a fruit (Fig. 1), leaving unsightly scarring. The beetles disappeared after about two weeks, without any insecticidal intervention. An assessment of damage three months later revealed no damage to any of the fruit remaining on the tree. This was probably because the initial damage took place very early in the season, leading to the trees selectively abscising the damaged fruitlets. Although not measured, there was no apparent resultant reduction in yield. These beetles were identified as Platychelus sp. (Coleoptera: Scarabaeidae) (Fig. 2), belonging to the tribe Hopliini of the subfamily Melolonthinae, known as monkey beetles (Péringuey 1902). It is easy to see how this tribe of beetles acquired this name, with extraordinarily long hind legs, increasing the overall length of the insect by almost 50%. The legs not only have the appearance of the gangly forelegs of certain monkey species, but this impression is further reinforced when one observes the beetles in movement.

South Africa is considered the global epicentre for endemism and diversity of monkey beetles. It is estimated that we have well over 1 000 monkey beetle species. However, only about half of them have been described and named to date. Mon-key beetles, many of which are brightly coloured, are known to simultaneously feed on flowers and pollinate them (Colville 2009). To date, only one South African monkey beetle species has been recognised to have any pest status, namely the Small Wattle Chafer (Monochelus calcaratus). It is a minor pest of plantation black wattles. Its larvae, which are white-grubs, may feed on the lateral roots of young trees, reducing growth and killing seedlings, whereas the adults may rarely defoliate trees (Prins 1965). However, this species is not closely related to the Platychelus species recently recorded on citrus. Ornamental flowers in gardens are occasionally attacked by any number of Hopliini species. In conclusion, we know very little about this monkey beetle species. It appears that this insect was an incidental visitor to the citrus orchards and despite the apparent damage at the time, no insecticidal intervention would have been justified. Additionally, there is obviously nothing registered for the control of these beetles on citrus, nor is there any knowledge in the public domain about their insecticidal susceptibility.

Opsomming

Talle klein kewertjies is in Oktober 2019 in die Gamtoosrivier-vallei, Oos-Kaap waargeneem waar hulle rondom die blom-kelke van sitrusvruggies gevoed het en die vrugte sodoende beskadig het. Die kewers is as Platychelus sp. geïdentifiseer, een van die baie soorte bekend as bobbejaankewers. Die ke-wers het binne twee weke verdwyn sonder dat enige insek-doders gebruik is. Drie maande later het ‘n opname geen skade aangetoon nie. Die bome het waarskynlik die beska-digde vruggies afgespeen omdat hulle so vroeg in die seisoen seergemaak is. Amper niks is oor dié kewersoort bekend nie, maar sy voorkoms op sitrus was waarskynlik toevallig en hy kan dus nie as ʼn sitrusplaag beskou word nie. ✤

↑ Figure 1. Monkey beetles feeding under the calyx of citrus fruit
(PHOTO: LUKE COUSINS)

↑ Figure 2. A Platychelus sp. monkey beetle
(PHOTO: LUKE COUSINS)