Scale Morphology Effects on Feeding Behavior and Biological Control Potential of Rhyzobius lophanthae (Coleoptera: Coccinellidae)

Abstract

We compared the morphological characteristics of the scale covers and bodies of 2 economically important scale species, California red scale, Aonidiella aurantii (Maskell), and oleander scale, Aspidiotus nerii (Bouche), to determine their protective value against predation by the coccinellid Rhyzobius lophanthae (Blaisdell). We also compared the morphology of the mandibles of R. lophanthae with that of Chilocorus cacti (L.), a specific predator of diaspidid scales. A higher percentage of R. lophanthae larvae survived when they fed on 2nd-and 3rd-instar A. aurantii and all stages of A. nerii than when they fed on gravid and parturient A. aurantii. Adult R. lophanthae took longer to consume 3rd-instar A. aurantii than 3rd-instar A. nerii and were frequently unable to penetrate the scale body of gravid and parturient A. aurantii. Predator preference for scale stage and species reflected the ease with which it was able to penetrate the scale cover and body of its prey. The hardened scale cover of gravid and parturient A. aurantii when coupled with the sclerotized scale body provided the scale with substantial immunity to predation by R. lophanthae for approximately two-thirds of the scale life span. We conclude that R. lophanthae is unlikely to suppress A. aurantii populations below those of economic concern when it is the sole biological control agent present. In contrast, the entire life span of A. nerii is vulnerable to predation, and this species appears to be suppressed to low densities by R. lophanthae.

Voracity of Coccinellid Species on Different Phenological Stages of the Olive Pest Saissetia Oleae (Homoptera, Coccidae)

“…The consumption of the different phenological stages of S. oleae depends mostly on the characteristics of the tegument of the prey [5], the relation between the sizes of predator and prey and also the nutritional quality of the prey [11]. Easily penetrated covers are more likely to be suppressed than thick covers [5].…”

“…Easily penetrated covers are more likely to be suppressed than thick covers [5]. In this way, it was probable that first instar nymphs are softer and easier to handle by smaller coccinellid species (e. g. S. mediterraneus) than the second instar nymphs.…”

“…Eventually, only C. bipustulatus can predate egg-bearing females because it possesses highly modified mandibles that are unique to the genus -they are acutely angled with a single tooth at their apex, which can be inserted between the scale and the substrate [5]. Other coccinellid species consume preferentially first and second instar nymphs of S. oleae that are abundant and accessible stages in summer and autumn in olive groves [8; Santos et al, unpublished data].…”

Ecological data of Lepidosaphes gloverii (Hemiptera: Diaspididae) in Greece

“…It has been reported that the development of R. lo phanthae on scales with harder scale cover [like Aonidiella aurantii (Maskell) and Chrysomphalus aonidum (Linnaeus)] is more difficult than on scales with softer scale cover (like Aspidiotus nerii Bouche) (Stathas 2000b, 2001b, Stathas et al 2002. Honda and Luck (1995) attribute the incapability of rearing R. lophanthe on diaspidids with hard scale cover to the morphological characteristics of its moufhparts. Bruwer and Schoeman (1988) reared L. gloverii in laboratory on several preys and tem peratures, and found that the mean optimum fecundity was 44.2 crawlers/female, in sour orange trees at 30°C.…”

How a slow-ovipositing parasitoid can succeed as a biological control agent of the invasive mealybug Phenacoccus peruvianus: implications for future classical and conservation biological control programs

“…It is believed that the cover might provide protection against predators (Foldi 1983;Gullan and Kosztarab 1997). However, this mechanism has not been so clearly described as in other scale insects with harder covers, such as soft (Hemiptera: Coccidae) and armored scales (Hemiptera: Diaspididae) (Daane et al 2000;Gullan and Kosztarab 1997;Honda and Luck 1995;Tena and Garcia-Marí 2008). On the other hand, the absence of a sclerotized cover allows mealybugs to carry out evasive movements similar to those performed by aphids (Hemiptera: Aphididae) (De Farias and Hopper 1999;Wyckhuys et al 2008).…”