No abstract

Antagonist interactions such as intraguild predation (IGP) or cannibalism among predatory arthropods can reduce the impact of these invertebrates on pest limitation in agroecosystems. Here, the effects of IGP between two major natural enemies of cotton pests, the cursorial spider Cheiracanthium pelasgicum (C.L. Koch) and the common green lacewing Chrysoperla carnea (Stephens), were studied under laboratory conditions. First, a feeding preference test was carried out to determine the degree of C. pelasgicum preference for lacewing larvae, using second-instar Helicoverpa armigera larvae as alternative prey. In a second bioassay, the effects of predator interactions on potential predation of H. armigera larvae were analysed using three treatment combinations (plus a control with no predator): (1) spider alone, (2) lacewing larvae alone, (3) spider + lacewing larvae. Potential predation by C. pelasgicum on lacewing eggs was also studied. C. pelasgicum showed no significant preference for either of the two species, indicating that this spider may impact negatively on the green lacewing population. Findings revealed no additive effects and an antagonist interaction between C. pelasgicum and green lacewing larvae, which adversely affected H. armigera suppression; both predators displayed lower predation rates when kept together than either predator alone. However, presence of lacewing larvae and subsequent unidirectional IGP did not affect the predation capacity of C. pelasgicum. Finally, predation rates of C. pelasgicum on lacewing eggs were very low (mean 2.35 ± 0.71 eggs, 24 h after offering) indicating that the impact of C. pelasgicum on lacewing populations may be limited.

No abstract

Intraguild predation (IGP) among predatory arthropods can impair pest control efforts and endanger the joint-action compatibility of groups of natural enemies. The present study used plant microcosms to examine IGP of Cheiracanthium pelasgicum (C. L. Koch) (Araneae: Miturgidae) on minute pirate bugs Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), two of the major lepidopteran-egg predators in southern Spanish cotton fields, and its effects on the control of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) eggs. Intensive unidirectional IGP of C. pelasgicum on O. laevigatus was observed under plant arena conditions: over 90 % of minute bugs were killed by spiders in the first 24 h. However, no negative interaction between C. pelasgicum and minute pirate bugs was found under different eggdensity conditions with Orius alone, and the combination of two predator treatments displayed significantly higher predation rates than the spideralone treatment after 24 h. Increased egg density did not affect control by predators, nor did it prompt a significant reduction in IGP. During a day-night bioassay, negative interaction between the two predators was found under night conditions, impacting on egg predation rates due to the combination of two predators. Predation of spiders on H. armigera eggs took place mainly at night, while predation by minute bugs was recorded both by day and by night. Finally, IGP by C. pelasgicum on minute pirate bugs was significantly higher by night. These outcomes demonstrate that diurnal and more intensive nocturnal IGP by spiders on minute pirate bugs had a moderate impact on the early control of H. armigera, with no negative effects after 24 h.