Comprehensive and Durable Modulation of Growth, Development, Lifespan and Fecundity in Anopheles stephensi Following Larval Treatment With the Stress Signaling Molecule and Novel Antimalarial Abscisic Acid

Abstract

The larval environment of holometabolous insects determines many adult life history traits including, but not limited to, rate and success of development and adult lifespan and fecundity. The ancient stress signaling hormone abscisic acid (ABA), released by plants inundated with water and by leaf and root fragments in water, is likely ubiquitous in the mosquito larval environment and is well known for its wide ranging effects on invertebrate biology. Accordingly, ABA is a relevant stimulus and signal for mosquito development. In our studies, the addition of ABA at biologically relevant levels to larval rearing containers accelerated the time to pupation and increased death of A. stephensi pupae. We could not attribute these effects, however, to ABA-dependent changes in JH biosynthesis-associated gene expression, 20E titers or transcript patterns of insulin-like peptide genes. Adult females derived from ABA-treated larvae had reduced total protein content and significantly reduced post blood meal transcript expression of vitellogenin, effects that were consistent with variably reduced egg clutch sizes and oviposition success from the first through the third gonotrophic cycles. Adult female A. stephensi derived from ABA-treated larvae also exhibited reduced lifespans relative to controls. Collectively, these effects of ABA on A. stephensi life history traits are robust, durable and predictive of multiple impacts of an important malaria vector spreading to new malaria endemic regions.

Aquatic Exposure to Abscisic Acid Transstadially Enhances Anopheles stephensi Resistance to Malaria Parasite Infection

“…Larvae were collected at 36 h following transfer of eggs into Nalgene pans and separated into four treatment groups. For each treatment group, 100 larvae were placed in 500 mL polypropylene Nalgene containers with 200 mL water with or without 1, 10 or 100 µM ABA (Caisson Labs, Smithfield, UT, USA) as described [20]. Due to the light sensitivity of ABA, 50 mL of water from each container was removed daily as described and replaced with freshly made ABA-supplemented water to yield a final concentration of 1, 10 or 100 µM ABA [20].…”

“…For each treatment group, 100 larvae were placed in 500 mL polypropylene Nalgene containers with 200 mL water with or without 1, 10 or 100 µM ABA (Caisson Labs, Smithfield, UT, USA) as described [20]. Due to the light sensitivity of ABA, 50 mL of water from each container was removed daily as described and replaced with freshly made ABA-supplemented water to yield a final concentration of 1, 10 or 100 µM ABA [20]. These concentrations were selected based on levels of ABA previously detected in water from inundated plant material under lab conditions.…”

“…These concentrations were selected based on levels of ABA previously detected in water from inundated plant material under lab conditions. Specifically, levels of ABA detected ranged from 0.5 µM to nearly 3 µM through 48 h after plant material was added to water [20]. Larvae were fed as described in Section 2.1. and maintained through pupation and eclosion to adults.…”

“…Relative transcript levels were determined for A. stephensi nos, ilps 1-5 and apoLp-III using previously published primers [20,25,30]. All data were normalized to transcript levels of A. stephensi ribosomal protein s7 (rps7) [20].…”

“…The presence of animal detritus in the larval environment as compared to plant detritus, has been associated with reduced development time, increased adult survival and increased adult body mass of Aedes albopictus [13] and of three species of the Anopheles gambiae complex [14]. Competition and threat of predation in the larval environment with decreased Lp levels and, therefore, decreased lipid transport and catabolism [20,27]. Second, in light of the comprehensive and durable effects of ABA larval treatment, we hypothesized that adults from ABA-treated larvae might exhibit changes in ilp expression that were similar to changes in ilp expression observed in female A. stephensi provisioned with ABA in a bloodmeal [25].…”