Recent trends in biological control of scale insects on fruit crops in India

Abstract

Scale insects are sap feeders, causing threat to the cultivation of several fruit crops. The scale insects can be grouped into two broad categories. The first group belonging to family Diaspidide, comprises many species of armoured scales (hard scales) belonging to the genera. <em>Aonidiella, Aulacaspis, Pseudaulacaspis, Hemiberlesia, Aspidiotus, Chrysomphalus, Pinnaspis, Parlatoria</em> etc. The second category belonging to family Coccidae comprises of the soft scales belonging to the genera Coccus, Puvinaria, <em>Chloropulvinaria, Saisettia, Parasaisettia, Vinsonia, Drephanococcus, Ceroplastes, Ceroplastodes</em>, etc. Scale insects are highly polyphagous, but certain species cause severe damage to specific fruit crops viz. the red scale, <em>Aonidiella aurantii</em> (Maskell) on citrus; latania scale, <em>Hemieberlesia lataniae</em> (Sign.) on grapevine.; white scale, <em>Aulacaspis tubercularis</em> (Newstead) on mango; green shield scale, <em>Pulvinaria psidii</em> (Maskell) on guava, lemon and sapota, <em>Pulvinaria polygonata</em> (Ckll.) on mango; green scale <em>Coccus viridis</em> (Green) on citrus and sapota and <em>Drephanococcus chiton</em> (Green) on ber and guava. Insecticides are not effective due to the presence of protective cover over the scales. On the other hand, scale insects are more amenable for biological control due to their sedentary habit and colonial distribution. Several scale insects are well regulated by the local predators. In nature, green shield scale, <em>Pulvinaria psidii</em> (Maskell) is kept under check by the predator, Australian ladybird beetle <em>Cryptolaemus montouzieri</em> Mulsant on guava, sapota and lemon. The reduction of the mango green shield scale <em>Pulvinaria polygonata</em> was attributed mainly to the action of the predators <em>C. montrouzieri</em> and <em>Spalgis epeus</em> Westwood. The green scale <em>Coccus viridis</em> on acid lime and white scale <em>Aulacaspis tubercularis</em> on mango are well regulated by the coccinellids <em>Chilocorus nigrita</em> (Fab) and <em>C. circumdatus</em> Sch. Local parasitoids are also known to effectively check the populations of the scale insects on different fruit crops. The encyrtid <em>Anicetus ceylonensis</em> How and the pteromalid <em>Cephaleta brunniventris</em> Motsch are responsible for the suppression of wax scale <em>Drephanococcus chiton</em> on ber and guava. The aphelinid parasitoid, <em>Pteroptrix koebeli</em> How. plays a major role in the regulation of the mango scale <em>Aulacaspis tubercularis</em>. On sapota, the aphelinid parasitoid <em>Coccophagus</em> sp. was the dominant natural enemy causing up to 95 % parasitism. <em>Scutellista cyanea</em> Motsch. (Pteromalidiae: Hymenoptera) was able to suppress <em>Parasaissetia nigra</em> (Nietner) on custard apple and pomegranate. In the absence of effective biocontrol agents in nature, parasitoids and predators have to be released in the field for obtaining an effective and quicker suppression of the scale insects. Release of adult <em>C. nigirita</em> was found to be effective in the control of the red scale on citrus in Karnataka, Andhra Pradesh and Punjab. Release of <em>C. infernalis (C.bijugus)</em> Mulsant @ 10-20 beetles/tree once in April-May has also been recommended to reduce Sanjose scale. The white halo fungus, <em>Lecanicillium (Verticillium ) lecanii</em> can be sprayed at 16 x 10<sup>6</sup> spores/ml along with 0.05% of sticking agents in the evening hours at 15 days interval to control the green scale in the hilly areas during cooler months. The biocontrol agents can be integrated with plant origin insecticides as they do not affect the activity of these agents.