Insect Pests of Fruits other than Citrus in Southern Rhodesia.
AbstractThe cultivation of fruits other than Citrus has not as yet assumed great importance in Southern Rhodesia, and they are not seriously attacked by insect pests. The fig is more subject to pests than others.
The fruit-piercing moths with a specially modified proboscis that have so far been recorded are: Othreis materna, L., O. fullonica, L., O. divitiosa, Wlk., Calpe provocans, Wlk., C. triobliqua, Saalm., C. emarginata, F., Serrodes inara, Cram., and Pericyma umbrina, Guen. Those with an unmodified proboscis are: Anua tirhaca, Cram., Achaea catella, Guen., A. violascens, Hmps., A. lienardi, Boisd., A. echo, Wlk., A. finita, Guen., A. sordida, Wlk., A. albicilia, Butl., A. trapezoides, Guen., and Sphingomorpha Morea, Cram. Notes are given on the bionomics and control of these moths together with a list of their food-plants.
Among the other pests dealt with are Ceratitis capitata, Wied. (Mediterranean fruit-fly), which is an introduced species. The eggs in summer hatch in 2-4 days. The ripeness of the fruit seems to have an influence on the time of hatching, and if it is too green the eggs may not hatch, or if they do, the larvae perish immediately. The larval stage usually lasts a fortnight to three weeks and the pupal stage in the soil from 12 to 21 days, depending on the season. The whole life-cycle at midsummer may last 28 days, and as much as 2 months or more in the winter. The females survive several months during the winter if no fruit is available for oviposition. The food-plants of this species are given. Two other species of fruit-flies attacking cultivated soft fruits are Pardalaspis quinaria, Bezzi (Rhodesian fruit-fly) and P. cosyra, Wlk.
Omophorus stomachosus, Boh. (fig weevil) is a well known South African pest and probably the commonest cause of stung figs. The eggs are inserted in cavities in the skin of the fruit and are apparently laid mainly in half developed fruits. They hatch in 3 days, and the larval stage lasts about 3 weeks, the pupal stage being passed in the fruit, which usually falls to the ground about this time, the adults emerging about 6 days later. It is probable that the weevil continues breeding throughout the year where fruit is available, but that the larval stage is prolonged in cold weather. In hot weather the whole life-cycle occupies less than a month, and it is possible that 4 or 5 broods may mature during the year. In any case the broods overlap very much as the season advances, so that all stages of the weevil are sometimes to be found in the figs at the same time. The adults not only feed on the fruit but gnaw the young bark of the twigs in the absence of fruit; they breed as freely in wild as in cultivated figs, but are not known to attack any other class of fruit. Infested fruit should be regularly collected and destroyed. The removal of wild fig trees, or the systematic destruction of their fruit, near cultivated trees is essential. During the summer the beetles may be shaken on to sheets spread below the trees. Possibly spraying with an arsenical compound might be beneficial. Heavy spraying with 1 lb. powdered lead arsenate to 30 gals. water early in September is worth a trial, and the addition of 6 lb. cheap sugar or 1 gal. molasses to each 10 gals. of liquid might make it more effective. In general it appears desirable to rely upon remedial measures other than spraying, which is mentioned for those who may wish to experiment.
A potential pest of some significance, which may have been confused with O. stomachosus, is Polygrammodes hirtusalis, Wlk. (fig Pyralid). A high percentage of wild figs are infested at Salisbury, but so far it has not yet been recorded on cultivated figs. Little is known of its life-history, but it has been bred out in numbers in September and November, whilst one adult was taken in January. Late in October 1922 the larvae were present in large numbers. A brief description is given of the adult and larva. When the latter is mature, it leaves the fruit and spins a cocoon in some convenient crevice, where it pupates, the adult emerging apparently within 2 or 3 weeks in the summer months. All infested fruit should be destroyed and wild figs in the vicinity eliminated. As the adults cannot be destroyed in the manner recommended for O. stomachosus, this Pyralid would probably prove more difficult to check after infestation of the crop had commenced.
Brief notes are given on the bionomics and control of various other insects that eat the fruit and attack the foliage, trunk, branches and twigs. Some pests of fruit prevalent in the South African Union, but not yet recorded in Southern Rhodesia, are Cydia pomonella, L., Aspidiotus perniciosas, Comst., Diaspis pentagona[Pseudaulacaspis pentagona], Targ., and Coryphodema tristis, Drury.