Fortified defence: Novel mechanisms allow a tree hole mosquito to resist predation from a predatory mosquito

Document Type

Article

Publication Date

12-1-2025

School

Biological, Environmental, and Earth Sciences

Abstract

Insects often use a suite of antipredatory defences to avoid predation. Although larval mosquitoes exhibit behavioural modifications to avoid aquatic predators, it is not clear if other antipredator mechanisms exist for this group. Larvae of the tree hole species Orthopodomyia signifera are known to coexist with the predatory mosquito Toxorhynchites rutilus, which often eliminates all other available prey. We tested three hypotheses that could explain how Or. signifera resists predation. First, Or. signifera larvae may exhibit behavioural changes that limit interactions with Tx. rutilus; second, their long thoracic setae may serve as a physical defence; and third, their unusual orange colour may reflect a chemical defence (aposematic coloration sequestered from secondary plant compounds from larval environments). We tested these hypotheses under laboratory conditions. For the first, we allowed predators to feed on either Or. signifera or Aedes albopictus, a species with short setae known to be susceptible to predation by Tx. rutilus. Late instar Or. signifera were then recorded in water from either trial to determine their behavioural responses to predation cues. For the second hypothesis, we amputated setae to determine if this affected predation by Tx. rutilus. Finally, we grew Or. signifera to late instars in water rich in tannins from natural tree holes or water lacking tannins and subjected those to predation by Tx. rutilus and recorded strike rates and handing times. When Or. signifera were exposed to conspecific and heterospecific predation cues, both caused Or. signifera to change to less risky behaviours, with conspecific cues causing the most stringent defensive behaviour. Amputation of setae from Or. signifera larvae led to mass drowning. However, we detected no differences in strike rates between Or. signifera (mean strikes = 2.38 ± 0.50) and Ae. albopictus (2.00 ± 0.49). Finally, regardless of an artificial or a natural diet containing secondary plant compounds, Or. signifera had significantly longer mean handling time (11,536.3 s) versus Ae. albopictus (4772.8 s), and Tx. rutilus made significantly fewer strikes after consuming an Or. signifera (0.25 ± 0.6) compared with Ae. albopictus (2.00 ± 0.49). Orthopodomyia signifera use both behavioural and an additional unknown antipredatory mechanism(s) to avoid predation by Tx. rutilus, a unique finding for mosquito larvae. Despite past research into larval mosquito predator avoidance, Or. signifera may be the first mosquito to be shown to possess multifaceted defensive capabilities. The complex responses to predation may suggest additional selection pressures experienced by mosquitoes and other insects not typically investigated.

Publication Title

Ecological Entomology

Volume

50

Issue

6

First Page

1033

Last Page

1043

Link to Full Text

Find in your library

Share

COinS