Insecticidal effect of Bacillus pumilus PTB180 and Bacillus subtilis PTB185 used alone and in combination against the foxglove aphid and the melon aphid (Hemiptera: Aphididae)

The foxglove aphid, Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae), and the melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae), are among the serious insect pests found in greenhouses. The efficacy of microbial control against these insects has been demonstrated and can be enhanced by the combination of different microbial agents. This study evaluated the efficacy of Bacillus pumilus Meyer and Gottheil PTB180 and Bacillus subtilis (Ehrenberg) Cohn PTB185, used alone and together, to control these two aphids both in the laboratory and in greenhouse on tomato, Solanum lycopersicum Linnaeus (Solanaceae), and cucumber, Cucumis sativus Linnaeus (Cucurbitaceae), plants. The results from the laboratory tests showed an increase in mortality induced by all biological treatments. In the greenhouse, all treatments induced mortality rates significantly higher than that of the control for A. solani. Similarly, all treatments performed better than the control against A. gossypii, significantly reducing its reproduction. Furthermore, we found no additive effects when mixing products nor negative interactions affecting survival for the bacteria investigated. These microorganisms therefore have potential for use in biological control.

Efficacy of Anystis baccarum against Foxglove Aphids, Aulacorthum solani, in Laboratory and Small-Scale Greenhouse Trials

A generalist predatory mite, Anystis baccarum (L.), has been identified as a key predator of small, soft-bodied pest species in various agroecosystems around the world. The foxglove aphid Aulacorthum solani (Keltenbach) is a new problematic pest in Canadian greenhouses. Laboratory colonies of A. baccarum were established and its predatory efficacy against A. solani was assessed. In laboratory trials, A. baccarum ate approximately one adult aphid or seven first instar aphids in 24 h. In a greenhouse bench trial on sweet peppers with the free-flying aphid parasitoid, Aphidius ervi Haliday, the population dynamics of A. solani in the presence or absence of A. baccarum was evaluated. Although the parasitoid alone successfully eradicated A. solani, when A. baccarum were present on the plants, the aphid population was eradicated more rapidly. Fruit yield was also 15% higher from plants where A. baccarum was released than the control (without A. baccarum). Furthermore, plants were naturally infested by Frankliniella occidentalis (Pergande) during the trial, which caused visible feeding damage to the fruits. Anystis baccarum also predates on thrips and thrips’ feeding damage to the fruits was reduced on plants where A. baccarum was released. Anystis baccarum was able to establish in sweet peppers and was determined to be complementary to the current practice of using A. ervi for the biological control of A. solani.

Aulacorthum solani (foxglove aphid).

A. solani is becoming an increasingly economic important pest of several agricultural crops worldwide and has recently undergone a status change from an occasional pest to a serious pest of vegetables and ornamental plants in greenhouses of North America and the UK (Jandricic et al., 2010, 2014a). A. solani was first recorded on citrus in the north of Iran in 2003-2004 (Alavi and Rezvani, 2007).

Development, Reproduction, and Life Table Parameters of the Foxglove Aphid, Aulacorthum solani Kaltenbach (Hemiptera: Aphididae), on Soybean at Constant Temperatures

We investigated several characteristics of the development and reproduction of the aphid Aulacorthum solani raised on soybean (Glycine max) at 10 constant temperatures between 2.5 and 30 °C, and described the relationship between temperature and several critical biological characteristics using mathematical models. We found that A. solani could survive and reproduce on soybean at temperatures ranging from 5 to 27.5 °C. High fecundity was observed at temperatures from 12.5 to 20 °C. The lower developmental threshold and thermal constant for this species’ nymphal stages were estimated to be 5.02 °C and 131.2 degree-days, respectively, using a linear model. The upper developmental threshold was estimated to be 33.9 °C using the Lactin-2 model. The optimum temperature for nymphal development was estimated to be 26.9 °C. The maximum total fecundity was estimated as ca. 76.9 nymphs per adult at 18.1 °C. The daily fecundity sharply increased at earlier adult ages, and slowly decreased thereafter until final parthenogenesis occurred, over a range of temperatures from 12.5 to 25 °C. The maximum daily fecundity was estimated to be ca. 6.1 nymphs per adult per day for a 5.2 day old of adult at 21.3 °C using an age- and temperature-dependent model of adult fecundity. In terms of life table statistics, the intrinsic rates of increase and the finite rate of increase were both highest at 25 °C, while the net reproductive rate was highest at 20 °C.

Short-Term Increases in Aphid Dispersal From Defensive Dropping Do Not Necessarily Affect Long-Term Biological Control by Parasitoids

Foxglove aphid (Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae)) is one of the principal aphid pests of greenhouse ornamental crops in North America. Biological control of foxglove aphid mostly relies on the use of Aphidius ervi Haliday (Hymenoptera: Braconidae). However, studies indicate that A. ervi may not be adapted to search for A. solani, and that in response to parasitoid attack aphids can drop and/or disperse, which may aggravate an infestation. Our goal was to further describe the searching behavior of A. ervi in the presence of foxglove aphids, the corresponding defensive behavior of foxglove aphid and the short- and medium-term effects on both pest dispersal and control by A. ervi. Behavioral observations were done on top and bottom leaves infested with foxglove aphid and a high release rate of A. ervi. Parasitoids tended to land on top leaves; however, more aphids were parasitized on bottom leaves, leading to equal numbers of parasitoid attacks in both locations. Most aphids dropped off the plant in the presence of a parasitoid. In large cage experiments, aphids were allowed to distribute naturally and A. ervi was released. The parasitoid still caused a high rate of aphid dropping. However, only a few aphids were able to successfully reach new plants, and most of these mummified over time. Our studies confirm that parasitoid-induced dispersal of foxglove aphid in greenhouse crops does occur, but also suggests this should not necessarily be a barrier to adoption of biological control, as A. ervi controls the aphids over time.