Persistence of soil and foliar azadirachtin treatments to control sweetpotato whitefly Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) on tomatoes under controlled (laboratory) and field (netted greenhouse) conditions in the humid tropics

Abstract

Persistence of neem-based products against sweetpotato whiteXy Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) was tested in air conditioned rearing rooms and tropical netted greenhouses (GHs). Two commercial neem products, NeemAzal ® -T/S (1% azadirachtin) and NeemAzal ® -U (17% azadirachtin), were used. Foliar application, under room conditions at dose-rates of 7 and 10 ml NeemAzal ® -T/S, induced an immature mortality of 32 and 44%, respectively, whereas 7 days post-application, under GH conditions, mortality rates declined to 5 and 7%, respectively. This result indicated rapid dissipation of the active ingredients. However, systemic application by soil drenching resulted in more stable eVects under both laboratory and GH conditions. After soil drenching with solutions of 3.0 g NeemAzal ® -U until 7-day, immature mortality declined from 88% for the Wrst day to almost half (45%) by day-7 in the GH, and from 90% on Wrst day to 64% by day-7 under laboratory condition. Similar response trends for B. tabaci were obtained for other parameters such as adult colonisation, egg deposition, and egg hatch. The loss of eYciency of the neem products was clearly related to dose-rate, methods of application, and environment (temperature and UV). Soil application is therefore, a convenient approach to achieve high eYciency and persistence with neem products under the conditions in tropical GH environments for whiteXy management.

Lethal and sublethal effects of azadirachtin on the bumblebee Bombus terrestris (Hymenoptera: Apidae)

“…It is constantly stated in the literature that azadirachtin is safe for beneficial arthropods 13 ; although our results have shown that the compound may affect B. terrestris with a range of sublethal effects, which are very important for the development and survival of the colonies. Here it should be remarked that, although the effects of this study were found under laboratory conditions with long-term chronic exposure which are unexpected under semi-field or field conditions with the low residual potential persistence of azadirachtin in these situations 38,48 , Africanized honeybees (A. mellifera) have been found to undergo lethal and sublethal effects on adult and larval individuals in their colonies when the foragers start to pollinate the Indian neem tree (A. indica), the plant from which azadirachtin is obtained 49 . The latter findings may indicate that the effects as observed upon chronic exposure to azadirachtin are conserved among bee pollinators and thus should not be neglected.…”

“…In this case, the recovery of reproduction measured as male progeny production, is probably related to the degradation of azadirachtin through time, which may have reduced poisoning, allowing egg laying and ensuring survival of the dominant workers and larvae, respectively. Azadirachtin kept into aqueous solutions and under low ultra-violet (UV) condition shows much less degradation when compared with dry surfaces and under high UV condition 37,38 . This probably contributed to the delay in 6 weeks of the egg laying of the dominant worker exposed to azadirachtin at 3.2 mg litre -1 in the laboratory bioassay without foraging behaviour.…”

Actividad biológica de nim en adultos de mosca blanca Trialeurodes vaporariorum (Aleyrodidae) West

“…A pest that affects a large number of agricultural crops is the greenhouse whitefly, Trialeurodes vaporariorum West (Hemiptera: Aleyrodidae), in this have been conducted studies with different products based on neem determining different effects; Margosan-O, Nim 80 and Nim Oil, causing significant mortality (Abou-Fakhr Hammad et al, 2000); while others like Azatin EC, Neemazal and Neemazal-T/S are excellent repellents (Cubillo et al, 1999;AbouFakhr Hammad et al, 2000;Silva et al, 2003;Kumar and Poehling, 2006). Some of these products like Nim 80 are efficient in all three aspects already mentioned, Islam and Omar (2012) and Nzanza et al, (2012) report these same effects.…”

Inert powders alone or in combination with neem oil for controlling Spodoptera eridania and Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae

“…The pesticides, when used improperly, can cause death, poisoning, production losses and increase insect's resistance, in addition to environmental and human contamination (GALLO et al, 2002). So, alternative control methods are being studied and used, including biological control, repellants or insecticidal substances which are naturally produced by some plants ( KUMAR;POEHLING, 2006;LOVATTO et al, 2004), as well as some products of mineral origin, like inert powders (LORINI et al, 2001;SANTORO et al, 2010). Regarding plants with insecticidal activity, neem (Azadirachta indica A. Juss) has been cited to be very efficient to control some insects species.…”