Sequestration and Transfer of Cry Entomotoxin to the Eggs of a Predaceous Ladybird Beetle

Abstract

In the past 10 years, sequestration of Cry toxins and transfer to offspring has been indicated in three insect species in laboratory studies. This work directly demonstrates the sequestration and intergenerational transfer of Cry1F by the parents of the aphidophagous coccinellid predator, Harmonia axyridis, to its offspring. Recently emerged adults (10 individual couples/cage/treatment) were exposed during 20 days to aphids (100 Myzus persicae each day) that fed on a holidic diet containing 20 μg/mL Cry1F (and a control-group). Egg batches and neonate larvae were monitored daily, and counted and weighed for immunodetection of Cry1F by ELISA. At the end of the bioassay, the parents were weighed and analyzed by ELISA. Cry1F was detected in the offspring, both eggs and neonate larvae, of exposed H. axyridis adults. On average the neonate larvae had 60% of the Cry1F concentration of the eggs from the same egg batch. The Cry1F concentration in the adults was positively correlated with the concentration in their eggs. These three results provided independent evidence of transfer to offspring. No detrimental effects of Cry1F were observed on the age of first reproduction, total number of eggs laid per female, age-specific fecundity, egg development time, hatching rate, or fertility rate. The occurrence and generality of intergenerational transfer of Cry toxins should be investigated in the field to determine its potential ecological implications.

Fig 1. Average (±SE) Cry1F concentration (ng per offspring) in egg and neonate samples: A) First egg sample to the tenth; B) First neonate sample to the tenth.

Averages are for 10 couples and averages followed by the same letter are not significantly different (Tukey’s HSD).

Fig 2. Relation between Cry1F concentration in parents (ng/mg F.W.) and the average Cry1F concentration in A) Eggs (ng/egg, r = 0.77; n = 10; P = 0.02) or B) Neonates (ng/neonate, r = 0.59; n = 10; P = 0.15).

Each point is a different couple (±SE). Adults are the average of both parents. Eggs and neonates are the averages for all eggs and neonates measured for each couple.

Fig 3. Average (±SE) age-specific reproduction.

A) Age-specific fecundity (m _x); B) Egg development time; C) Fertility; D) Hatching rate. Age averages with different letters are significantly different (Tukey’s HSD). For egg development, * = abc, ** = bcd. For fertility and hatching rate, averages were separated by confidence intervals on the age-specific parameter estimates.

Fig 4. Relation between female weight with average age-specific fecundity and egg development time.

Control showed significant correlations while the Cry1F treatment did not.