Temporal and spatial changes in aphid and parasitoid populations following applications of deltamethrin in winter wheat

Abstract

The spatial and temporal effects of the pyrethroid insecticide, deltamethrin, on populations of cereal aphids and their primary parasitoids and hyperparasitoids were investigated in a large scale field experiment in winter wheat. Four hectare plots were treated at the recommended field concentration or a reduced concentration representing one twentieth of field rate. A control plot was left unsprayed. Invertebrate populations were sampled at sites within a grid layout covering the whole plots, enabling the use of geostatistical analysis. Hymenopteran populations were monitored using transparent sticky traps and suction sampling. Aphid populations were recorded by visual counts. Monitoring continued for 36 days after treatment. The full rate deltamethrin treatment resulted in initial reductions of aphid populations by 78%. Primary parasitoid and hyperparasitoid populations were reduced in suction samples by 90% and 47% respectively, when corrected for control fluctuations. The reduced deltamethrin concentration caused reductions of aphid, primary parasitoid and hyperparasitoid populations of 40, 60 and 54% respectively. Aphid population recovery over the full rate plot occurred slowly and in a 'patchy' manner following treatment. No significant reinvasion gradients were detected. Aphid population density recovered more rapidly in the reduced rate treatment; with initial evidence for increased densities at the plot centre. Significant patterns of reinvasion were initially detected for both groups of Hymenoptera in the full rate treatment, suggesting that reinvasion of the sprayed area was taking place from untreated surrounding reservoirs. It was concluded that experiments that examine pesticide impacts within small plots will lead to underestimates of effects on dispersive groups including parasitic Hymenoptera.

Effects of pesticides commonly used in peach orchards in Brazil on predatory lacewing Chrysoperla carnea under laboratory conditions

“…The less persistent pesticides, abamectin and trichlorfon, whose effects last less than five days are likely to have less impact on the population of the natural enemy in the field compared to the persistent phosmet easily allowing the ''vertical colonisation'' via emergence of treated cocoons [a high degree of protection against all the insecticides tested was provided by the silken cocoon, as previously stated by Medina et al (2001)], as well as ''horizontal colonisation'' from the reinvasion of the depleted areas from the undepleted surroundings, with a similar pattern to that described by Longley et al (1997) in the case of aphids parasitoids in winter wheat crops treated with deltamethrin.…”

Within-field distribution of the damson-hop aphid Phorodon humuli (Schrank) (Hemiptera: Aphididae) and natural enemies on hops in Spain

“…By contrast, Ruggle & Holst (1995) studied a 60 m by 40 m area within a winter wheat field and concluded that aphids were concentrated in the centre of the field when population levels were high. Longley et al (1997) studied the spatial and temporal distribution of aphids and parasitoids following insecticide application in winter wheat in the UK whilst Schotzko & Smith (1991) demonstrated that the host plant (winter wheat) itself may influence aphid distributions.…”

<I>Diaeretiella rapae</I> Limits <I>Myzus persicae</I> Populations After Applications of Deltamethrin in Oilseed Rape

“…This dynamic has been particularly well documented under laboratory conditions (Waage et al 1985). When recolonizing a crop after insecticide treatment, parasitoids may return to depleted areas (where insecticide treatments have been done) from undepleted surroundings (Longley et al 1997), a process called "horizontal recruitment." In addition, a process of "vertical recruitment" of parasitoids (i.e., the emergence of adults from mummies) may occur in the treated crop.…”

“…For example, pest resurgence or an increase in populations of secondary pests can occur as a result of the death or perturbation of beneÞcial arthropods by pesticides (Hardin et al 1995, Longley et al 1997. Parasitoids can be exposed to insecticides through spray droplets (Jepson 1989), through residues on the crop foliage when foraging (Brown 1989;Jepson 1989;Longley and Jepson 1996a,b), or when feeding on contaminated water droplets, nectar, or honeydew (Longley and Stark 1996).…”

“…For example, deltamethrin treatment was shown to result in a 90% reduction in the number of parasitoids and a 78% reduction in the number of aphids (Longley et al 1997). After insecticide treatment, pest and parasitoid populations may recover differently because their varying susceptibility to insecticides (Croft and Brown 1975, Rajakulendran and Plapp 1982, Weires et al 1985 and reproductive rates (Longley et al 1997). This dynamic has been particularly well documented under laboratory conditions (Waage et al 1985).…”