Retrospective analysis of a classical biological control programme

Abstract

Classical biological control has been a key technology in the management of invasive arthropod pests globally for over 120 years, yet rigorous quantitative evaluations of programme success or failure are rare. Here, I used life table and matrix model analyses, and life table response experiments to quantitatively assess a classical biological control programme for an invasive insect pest in the western United States. Life tables and matrix models were developed for populations of Bemisia tabaci (sweetpotato whitefly) on cotton in Arizona before (1997–1999) and after (2001–2010) the permanent establishment of two exotic aphelinid parasitoids. Analyses tested multiple hypotheses relative to the expected outcome of a successful programme. Marginal rates of parasitism, rates of irreplaceable mortality from parasitism, total generational mortality and finite population growth (λ) were unchanged for B. tabaci populations before and after exotic parasitoid establishment. Prospective analyses showed that predation during the final nymphal stadium had the greatest influence on population growth rates regardless of parasitoid establishment. Retrospective LTREs showed that predation and unknown mortality contributed most to changes in λ after parasitoid establishment. Marginal parasitism acted weakly in a direct density dependence fashion after parasitoid establishment, and for all 14 years combined. However, this did not translate into an association between pest population density and marginal rates of parasitism for the 10‐year period following establishment. Synthesis and applications. Rarely are classical biological control programme outcomes assessed rigorously. Life tables, matrix models, and life table response experiments showed that the decline in the pest status of Bemisia tabaci (sweetpotato whitefly) was not associated with the establishment of two exotic parasitoid species in the cotton system. Instead, native arthropod predators play a major role in pest dynamics. Further efforts to enhance conservation of the extant natural enemy community, with focus on increasing mortality in final stage nymphs and adults, may be the most efficient means of increasing biological control services. Analyses deployed here should be more widely applied to assessing and improving biological control generally.

Can Generalist Predators Control Bemisia tabaci?

“…Additionally, third and fourth instar nymphal mortality is linked to the same above species along with L. hesperus and Geocoris pallens Stal (Hemiptera: Geocoridae) [ 44 , 45 , 46 ]. Consistently, in a long-term life-table study spanning 14 years, the highest mortality attributed to generalist predators is on fourth instar B. tabaci nymphs, followed by eggs and other nymphal stages [ 20 ]. Furthermore, initial results from incorporating natural enemies into the current economic threshold for B. tabaci also suggest life stage-specific contributions in whitefly control [ 19 ].…”

“…To our knowledge, no US studies have evaluated the effect of landscape complexity on B. tabaci abundance and its predation. Further, while several studies have reported the potential predators of B. tabaci [ 17 , 19 , 20 ], the effect of predator richness and diversity in response to landscape structure on B. tabaci population dynamics has not been studied in the US agroecosystems. To build area-wide pest management strategies for B. tabaci , research is needed not only in cotton fields but also in vegetables.…”

“…Conversely, if predator consumption of whiteflies does not overlap between species (i.e., predator complementarity) either in time or space, the efficacy of biological control may be enhanced [ 15 , 16 ]. Encouragingly, studies in the southwest USA provide evidence that generalist predators can contribute significantly to B. tabaci control [ 17 , 18 , 19 , 20 ]. Although past reviews identify several potential predators likely contribute significantly to B. tabaci biological control, except in rare examples, their contributions are not fully integrated into B. tabaci management.…”

Cover crops improve early season natural enemy recruitment and pest management in cotton production

“…Although relationships between cover crops, density and diversity of predators, and pest pressure are evident, further research is needed in guiding pest management thresholds and inputs into the system in relation to cover cropping system used and quality of the cover crop. Lastly, research demonstrates that native predators are particularly important in cotton production (Naranjo 2018), and the effectiveness of predator diversity in providing biological control is closely linked to the composition and function of predators in the field (Heimpel & Mils, 2017); therefore, our future work will untangle how management strategies influence the composition and functional roles of native predators in cotton systems.…”

The Parasitoid Eretmocerus hayati Is Compatible with Barrier Cropping to Decrease Whitefly (Bemisia tabaci MED) Densities on Cotton in China

“…As a solitary primary parasitoid, E. hayati shows high preference for B. tabaci on various host plants, including tomato, eggplant, poinsettia, and cotton [32,[35][36][37]. Although the release of a parasitoid could suppress whiteflies, this has not always been observed [34,38,39]. In such situations, combination of various methods may offer a solution.…”